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Some hints for determining the age of equipment not marked on serial plate,dating old kit. The best is date codes on ICs. These are usually 3 numbers say 712 distinct from the IC type number which is usuallly letters then numbers. For 712 12 is the number of weeks (ie march) into the year ending 7 . But is it 1977 or 1987 etc. The 70s printed numbers are usually more angular as though printed in the fonts available to an XY plotter. Also the IC series number is usually indicative of the era. For Sanyo ICs a number like 4C1 probably means 1984 from the '4'. Larger (power handling) package/hybrid ICs of the 70s were a lot less standardised than later. Other indicators dark brown paxolin board would suggest 60s rather than 70s as would carbon resistors rather than metal oxide (no bulges at the ends of the barrel). Also the sizes of 60s and 70s resistors tend to be larger than what is actually required for heat dissipating. E-line transistors come in the 80s . Places to find dates are sometimes large electrolytic capacitors, polycarbonate capacitors,large transformers,loudspeakers ,relays, microswitches,motors , some small rectangular radial lead caps ,body of air vane tuning caps and some small transistors have a datecode. Clear wrapped ribbon cable tends to be 70s, grey covered ribbon cables tend to be 80s and thin tape type with foil conductors tends to be 90s. PCB traces from 60s onwards tend to get less angular and more curved by the 90s ,double sided traces on boards tends to be 80s onwards. The year of introduction of certain types of connectors gives a lower bound. eg Scart/Peritel would not be found earlier than 1977 and those would be in French kit, the earliest date for mini-din would seem to be 1985. The pitch of IC pins of course gets less than .1 inch only 80s onwards and surface mount tends to be 90s onwards. LEDs started coming in early 70s. For Technics / Panasonic ICs of the 1970a date codes probably take the form a single number then in smaller script an underlined HEX digit. ie 9 plus small underlined D would mean 1979 14/16 ths into the year. After year 2000, eg 5007 presumably week 07 of 52 in year 2005 JRC IC maker seems to use this convention of reversing post-millenium dates - do others ? Unless you find 2 or more IC date codes from different manufactirers agreeing it is often more a feel or balance of probabilities for a date. Date marks on mouldings and PCBs Moulding example Plastic moulding with raised print 82 83 84 85 with a small moulded pip over both 82 and 83. Then a 1 to 12 'clock face' both with an arrow next the figure 8. A centre pop dimple in the mould above 82 in 1982 and then another over 83 in 1983. Leading to raised small conical pips on the plastic. Probably means 8/12 year or August 1983 PCB example White silkscreen printed panel on the overlay of a PCB, presumably with date coding. A left panel and right panel consisting of 1 to 6 along top and 5 dots in each column so 6 x 5 dots Right panel marked 7 to 12 and similar array of dots but the third one down under the 7 was missing. Probably third week of 5 weeks of July. Central panel had marked like this 02 ?? ?? 05 The queries were probably the remnant tops of numbers from scrubbed out 03 and 04 so probably like in the plastic case 03 is scrubbed in 2003 and 04 scrubbed in 2004 but still leaving the 03 mark. So probable screen printing date of mid July 2004 Tip for Vinyl record decks with small weight anti-skate mechanism. Where the cord is looped on to the anchor rod push a plastic circlip over the end of the rod to stop the cord dropping off. Anglepoise lamp/ Luxo lamp. Usually used with a maximum bulb rating of 60W but if you use a directed photoflood type lamp with internal silvering that directs light and heat forwards you can go the 100W without the lamp shade/ lamp socket getting excessively hot. Tip for bodge "repair" to awkward slide switches with poor contacts. Probably no good long term but for the situation where it is part of a ganged switchway and a hell of a workup to replace. Only for use on low voltage switches. If cross contact conduction produces crossover or distortion then you will have to replace anyway. At the top of these ganged switches is often a small hole. Make a small ring of "blue-tak"/plasticene and scoop graphite into the hole. Then with the thin bore plastic tube of a can of switch cleaner squeeze the blue tack around the end so you can blast graphite into the switch with the cleaner. If this doesn't work then inject graphite and silica gel (silicone grease) paste into the hole in similar manner. Use a syringe perhaps with small bore piece of polythene tube attached if resticted access. Large feet for large kit like stage amps. Use rubber door stops from ironmongers. Or cheapo sink plugs with centre mount removed and packed out inside with washers and stained black. Use the other way up as skirts around and under cracked existing feet to reinforce them. HH amplifiers etc, broken end-cheek carrying handles. Black plastic handles that are broken on one side only not totally broken but dangerous and weak and too small a cross-section to glue. Or reinforce a 30 yearold handle before it breaks (replace glue for heatshrink). Cut a length of large heat shrink and slide/pull through the break to lie around the handle. Chain drill 2 slots either side of the handle in main body of end-cheeks. Pass one 10 mm cable tie through these slots and another through the heatshrink. Pull tight with 2 sets of pliers. Heat the shrink in place. Replacing pivotted parts using torsion springs eg cassette holder flaps and cassette write-protect sensing arms, often in awkward positions so cannot hold back the free end and fix in place at same time. Hold the spring back with a small cable tie around the part and spring end. When replaced cut the cable tie IF coil alignment tools for the ferrite slugs A good starting point for making is to find some plastic dart stems that no longer hold their flights/fleches. Cut down with knife or small grinder. Counting-off turns prior to coil rewind. If the coil has undergone long term heating the enamel on the wire can part melt / fuse so play a low temperature hot air gun on the coil while unwinding on a coil winder machine. General point pull the retrieved wire away from end faces to avoid snagging and also go slow at ends as more likely to have dropped inwards over time with thermal changes. If the layers are disturbed at one end so they 'underlap' with the wire breaking then cut down to the bobbin core leaving that section till end and cut off and count by eye. Count the remaining major section off 2 layers at a time. Count off what you can and remainder, if continally breaking (eg 40 to 46 SWG), then cut axially with a knife , pull off and count by eye and weigh a representative section, then weigh total mass of coils to determine ratioed, the number of turns. Missing ceramic reonator in remote control Get some salvaged resonators and try each in turn 300,400,455 and 500 KHz would be the most common used. Or try a medium frequency generator of a few volts pk-pk fed into the resonator pads and see what effect on receiver with different f settings when a key is pressed. Disassembling standard ball races. That is for cleaning or the anulus rings make good packing pieces for adapting things to shafts. Also perhaps where a race needs replacing but cannot release and can get away with replacing ball bearings only. Prize off the ball separating ring that is push fitted into the outer anulus. Then in a box, to catch the balls, move all balls to one side and central anulus will move to release the bearings. Ball bearings from ball races tend to be very accurately machined to standard dimensions useful for guaging dimensions in awkward places. Front panel illumination. Instead of festoon bulbs or numerous bulbs consider computer case gizmo elecroluminescent panel or string fed via small inverter from 5 or 12V. Cable hank hooks for backs of amps to wind the mains cable around. Plastic 22mm pipe p-clips/nail clips , single fixing like electrical surface wiring clips but larger. Hold the fixing end and the open hook end with smooth pliers and heat the inside surface with a low set hot air gun until soft enough to straighten out and let cool. Or 22mm overflow screwed pipe clips, hacksaw off one horn and cut away the support of the other before melting. If only white or grey ones available then do like in the "japanning" tip, but at lower temp. "Japanning" bolts for cabinet fastening. Gives a more durable finish than painting with ordinary black paint. A use for that photocopier toner in the used/recovery bottle, or if access to old coloured toner for coloured printing on photocopiers (not modern colour photocopiers) you can do other than black. Cover the thread of the bolt with kitchen foil, grip in pliers and heat up , to well over fusing temperature, with a hot-air gun and dunk in a pot of toner. Rattle off excess coverage and excavate excess in the slot with a needle while still hot. Blown primary, how to determine unknown secondary voltages and current ratings of a mains transformer Simulating a multi-secondary transformer using a known good one but not using the primary, to get some data. I used a variac supply near the bottom of its range at 18volts and a 25 ohm, 20W dropper to feed 50Hz (UK)ac into a secondary. Assuming you have a reasonable idea of the voltage of one 'unknown' secondary. The transformer I used first was a high grade enclosed Gardners, 1.3Kg but only 15W combined outputs, 240V (UK) with marked 2 separate secondaries of 6.3V, 0.6A and a 150-0-150 at 25mA. With 3.43V ac on one '6.3V' secondary there was open circuit 3.40 on the other isolated '6.3' and 161.4V end-to-end on the '150-0-150' and incidently 116.4 on the primary. Then loading with different resistors 100K, 161.4 drops to 159.1 5.8K on 161.4 drops to 55.8, 3.43 input drops to 1.64 swapping to 5.8K on 3.4 , no change 1K on 161.4 to 12.1 and 3.43 to 0.771 swap to 1K on 3.4 , drops to 3.39 270 ohm , 161.4 to 3.34V 270 on 3.40, drops to 3.37 56 ohm on 161.4 to .704 and 3.43 to .54V 56 on 3.4 , drops to 3.28 and 3.43 to 3.42 8.2 ohm on 3.4 , drops to 2.55 and 3.43 drops to 2.99V A bit more generalised. Noting that for one secondary for this test transformer was rating 300V, 25mA then V/I of 12K and the 6.3V, 0.6 secondary of 10.5 ohm. Doing as before powering a 6.3V secondary to 3.43V and '300V' was 161.4V then loading it until the voltage ratio was 80 per cent that is 161.4V down to 101.5V and 3.43 falling to 2.69V so 101.5/2.69 = .8 then that R is 12K. So for similar transformer construction and high V, low I then find that value of R for 80% then if V is known then current rating is V/R. Doing the same for the low V,high I one then for R=10.5 ohm then corresponding ratio drops from 1:1 ie ==3.43:3.4 down to 3.03/3.43 is 88% for high current , low voltage. So for similar transformer construction and high I, low V then find that value of R for 88% then if V is known then current rating is V/R. Other clues would be the gauge of the wires if they can be seen and the overall size and weight giving an idea of the overall power rating. Resistance checks would show which are more likely high V or high I. An ac inductance meter will give some useful information also. Second test with a more basic Albion make, .8Kg, 20W open construction 245V primary, 2 secondaries 17V,1A and 6.3V,.6A. Again putting current into the lowest secondary giving 5.59V on '6.3' and 14.52 on '17' (185.8V on 'primary') 6.3/.6 wire was 24thou diameter and 17V,1A wire was 27 thou diameter. 17/1 = 17 ohm. This time loading the 17V secondary with 17 ohm meant the ratio had dropped 69 per cent (15.52/5.59 to 2.778/1.544 ) Usually you would get some idea of one rectified V from max or min, by capacitor ratings or a regulator voltage etc. For main filter caps reduce to x0.75, then divide by about 1.4 to get an RMS secondary voltage. Valve radios would have one secondary connected to the heaters so usually 6.3V. A vacuum fluorescent display is likely to have an isolated feed in the range only 2 to 5V Toroidal transformer 2x 120V to 2x 15V,2A, .75Kg and 2A wires 33 thou diameter. Characteristic R = 15/2 = 7.5 ohm. Critical ratio in this case was 82 per cent with 7.5 ohm. 15.27 input on '15' giving 15.26 on the other and 108V on one of the primaries. With 7.5 ohm 15.27 i/p drops to 3.91 and 15.26 drops to 3.19. For a large toroidal 500W 2x 35V, 7.1A , weight 4.8 kg Secondary wires consist of 2 paralled 56 thou diameter wires per secondary. Characteristic R= 35/7.1 = 5 ohm. With 15.16 on one 'secondary' 15.1 on the other and 49.8V on a 'primary' 15.16 dropped to 2.59V and 15.1 dropped to 2.46 so characteristic ratio is 95 percent for this transformer. High voltage for portable equipment. Like HT for a Guiger Mueller tube Use something like a 240V / 12V transformer the wrong way round. An oscillator not necessarily 50/60Hz , pick the most efficient f, via switcher transistor to the 12V coil Problems with ceramic daughter boards with SM devices. Often a problem in Akai VCRs. All painted with epoxy? black paint and themal variation or chemical action must force the SM chips away from the board. As no known solvent for clearing off the epoxy a matter of draping nylon cable ties and halved clothes peg wedges around the ceramic board and chip to physically hold down in place. Tie the wrap and then force in the half-peg wedges to tighten down sufficiently - lovely bodge. Magnifying spectacles Starting with 2.5 dioptre reading specs (dependant on the person's sight) and a cheap and nasty pair of plastic binoculars - did't even state manufacturer or mag. but about 9x30mm. Two monocular barrels without pentaprisms and central flat section with double pivots and thumb-screw. Remove the front double 30mm lens section and mount on the specs with a couple of plastic cable clips, nylon pcb stand-off and glue. Gives double monocular, not binocular, of about 4x mag. and 130 mm of clearance in full focus depth. Callibrating a DVM and cross-calibrating a standard cell For anyone with access to a Weston cell but not access to a 5 or 6 digit DVM. I think this is how I cross-calibrated. I've dug out the docs and mine was calibrated at manufacture as 1.01866V at 20 deg C and -40 ppm/ deg C , 14 March 1979. estimate of uncertainty 10 ppm About 2002 I did the following with my cell and someone else's secondary standard cell. My DVM has a 300mV range for its 4 digits, or 200mV will do the same. With a NiCad in good condition in mid discharge and left for some hours to reach room temperature is a nominal 1.2V. What the actual voltage is does not matter as long as it is stable. Assume for convenience here 1.2V. Only use with DVMs ( high input impedence) . Then commoning negatives of Weston cell and NiCad, measured the difference so came in the 200mV range. Which brings it into the first digit '6' of 1.01866 then ratioing of the flashing digits gives an estimate for the fifth digit. So reading of 181.4 mV With DVM 2/3 time reading 181.4 and 1/3 time reading 181.3 so implying about 181.37mV and Weston Cell voltage of 1.01863 at 22 degrees C. The other calibrated cell / DVM test was about 1/3 to 2/3 the other way round on last digit agreeing with that cell's yearly calibration value, allowing for 22 deg C. At the same time I checked a small Muirhead standard cell salvaged from a bit of kit and it too was many years old but almost the same voltage, only last digit (ie 1.0186*) different again. Splicing broken audio cassette tape. REquired a "stickit note" - where a bod was trying out glue formulations and one failed miserably,just a tackiness - what can we market it as. ? Anyway lay overlapped ,in line the broken ends ,active ferrite side down against the glue. With a razor cut diagonally and remove the surplus triangle of tape. Cover with some thin vinyl tape. Turn over and remove the stickit note,the other surplus triangle and pair back the surplus vinyl tape. "Hub puller" for CD mechanism platter/spinner removal or can be adapted for small motor metal-pulley removal. Required some perforated metal ( 1/4 inch hole spacing ) - if staggered lines and rings of 6 holes around each hole then easier. The material I had was internal aluminium divider plate from a scope, about 0.04 inches thick. Cut a strip 3 holes wide and about 17 holes long. Cut a central V notch so can slide under the platter and lie centrally. Bend up into side view D shape and bolt together around cental hole. The central hole takes a 4 mm hex head 25 or 30mm high-tensile machine bolt and nut that can be restrained/locked in place by the 4 small 3mm , countersunk heads, if suitable hex nuts, surrounding the 4mm nut . Grind the end of the 4mm bolt down in diameter by holding in a loose sleeve so can rotate round while grinding, slightly tapered, so the tip, plus a bit, is less diameter than the motor spindle. Measure the gap under the spinner with feeler guages. Grind/file any edges on the D-strip, assemble and place over the platter, tightened into the spindle hole with allen key. Surround with some card to protect from direct heat and heat the central platter/ motor spindle with hot-air gun. With luck there will be a click on initial shifting or re-engage hex key and turn some more . Remove and with glove and allen key push further. Instead of making long thin and fragile bolt end use small ball bearings as packing pieces to continue removing the platter. To replace then heat up and using a glove place back on shaft with feeler guages in place for correct gap. Loudspeaker coil rewinding. 46V DC on 8 ohm 10 inch speaker, didn't last long, going o/c. Decided to try rewinding as I've never tried it before. Found a clean way to remove the cone from the frame. Desoldered the braid connections, indented with a centre punch through the cone periphery into the steel frame for re-alignment. Heating the frame with a hot air gun and pushing the periphery of the cone with a well used and rounded wooden kitchen spatula, separated cleanly from the gummy glue. Put in spacers to stretch the inner dust diaphragm and hot air gun heating unglued the periphery of that corrugated disc. I didn't expect to see what was inside. A burnt mass of wire and the innermost end of the penetrating lacquered paper cylinder neatly burnt off in a perfect ring. Gap in magnet about 66 thou, paper cylinder about 5 thou thick and 2 layers of about 2 x 30 turns of 6 thou wire (originally). I don't fancy trying to rewind on a small paper cylinder and fixing to the remnant all with such XY&Z precision to clear that 2x 25thou slot gap in the magnet. Decided I'd throw it out as a cheapo one anyway. I imagine winding the wire over the lacquered paper on a mandrel and perhaps some 25 thou shim material in outer part of the gap temporary on re-assembly. Some flattened while molten hot melt glue string around the periphery. Clamped temporarily in place on the rim, powered up with a watt or 2 and cone radially pushed N,E,S,W for problems before final heating to set the rime band and perhaps repeat active test again before regluing the dust diaphragm. Looks as though such speakers use a sort of air bearing/ ground effect. Inside diameter of the slot in the magnet something a bit less than 1.502 in so probably 1.5 inches. Inside diameter of the paper cylinder that goes inside the magnet gap about 1.65 inches so with a gap width of bit greater than 66 thou and paper plus double thickness coil of 15 thou means the wire cannot touch the outer diameter of the magnet gap. And I just cannot believe that in all operational circumstances that the inside of the paper cylinder can never touch the inside surface of the slot with only 7 thou of clearance. A silicone treatment to the inside surface of the paper cylinder would make sense. Knowing that I might have a go gluing a new bit of cylinder and new coil to the existing remnant of cylinder as there is plenty of external room for excess glue/binding. As a mandrel a cassette DC motor is about the right diameter and also for winding purposes it might be more practical putting the spindle in a vice and winding over the motor rather than using a winding machine as the end of layer reversal needs to be more accurate than usual coil winding. REW and FF problems with always laced "wrap around head drum" vcr types Assuming no problem with the motor or slip clutch ie putting a doab of correcting fluid on the exposed end of the capstan spindle shows the motor slows down when the tape tramsport slows down. Problems particularly with REW when most tape is on the supply reel or FF when the take -up spool has most tape. Try with fingers either side of the drum for tape tension. If the leading tension is noticably more than the lagging tension then try the following. Paradoxically try increasing the braking tension by upping the spring guage. The felt on the brushes and the areas on the spools probably polish with age. There is a "skin effect" between the spinning head drum and the moving tape. Too little back tension and the aerodynamic cushion disappears but increase the back tension pulling the tape closer to the drum initiates this air cushion and reduces the drag. On opening the case of some non-working kit. Have a good sniff,phenolic smell for burned boards etc and there is a distinctive (fishlike) smell to the electrolyte leaked out of some electrolytic capacitors. First things to look for with broken equipment after being dropped. Cracked pcb and traces especially the brown "phenolic" unreinforced boards particularly where there are connections such as sockets and switches between casing and pcb. Broken joints to massive components such as transformers, large capacitors etc. For digital / micro based equipment one of the first things to suspect is any crystals as the internal connections are little more than friction and the quartz sliver is easily cracked. Ceramic resonators are similarly prone to failure under shock loading. Surface mount components easily can have a few contact legs break away not having the thru board mechanical location of conventional components. Replacing insulated back TO220 power trannies with non-insulated. Use a sheet of mica TO3 sized or larger and it will often register with surrounding parts avoiding having to fix against slippage when using the original power trannie retaining clips. Use thermal conductive grease. I prefer to use metal backed ones as the thickness of mica is about a tenth of the thickness of the plastic insulation on the insulated types so insulated against heat transfer to a greater extent as well. Internal and external circlip pliers for the very small sizes. Adapt an old pair of long nose pliers that have seen better days. Just back from the tips grind a back angle on each internal face just a couple of mm enough to grip the circlip without slipping. Preferably on another pair of small old long nose pliers so as not to weaken the points further grind faces on the external edges for external circlip pliers. Force handles outwards to use. If more force is required use "folding wedges" (pair of small greased wooden wedges back to back) and packing piece between the handles Removing pulleys/cogs off the shafts of small motors. Sometimes ,especially interference fits of steel cogs on steel spindles, the normal heating with a hot-air gun and levering with a screwdriver blade between cog and body of motor would mangle the brushes or bearings. Mount the heated cog in the soft jaws of a vice and hammer the end of the spindle with a pin punch or "pop-rivet" (blind tension rivet) with end ground to give plain bearing face. Situation where I had a stubborn steel cog that I would have had to grind off to use the motor for another purpose with a brass pulley off a motor with larger spindle. Instead of grinding off ;powered up the motor and carefully ground down the diameter of the steel cog against a spinning grinding wheel stopping to measure the diameter a few times. Brought the diameter down to be an interference fit for the hole in the brass pulley. Letting the steel cool/cooling with freezer spray and heating the pulley to mate. I would have hade to make an adapter to match spindle to hole in pulley. Keep a radio on near your workbench. It can sometimes indicate a problem with mains switches where there is a prolonged crackle rather than a simple click. Removing / replacing vol/balance/tone pots on amps etc Where the pot is close to the chassis and after desoldering the pins there is not enough leeway to remove the pot. The alternative is to remove the whole circuit board from the chassis. With a ball mill in a Dremmel open up the chassis on the away side from pcb side of the hole for the pot bush after removing the pot bush nut. So making a small "slot" to give more angle to release the pot pins from the pcb holes. Maybe open up the anti-rotation location pip hole as well if that is relevant . Push down on the pcb to give a bit more clearance as well. Clean up /enlarge this slot to assist refixing Speaker grille cloth Specially the metalised fancy stuff where a section comes loose and droops. Should be under "T" section trim. Whith "sharlened" chalk mark the continuation of the line from the still trimmed sections along the sagged bit. Push a drawing pin at either end before lifting the trim. Starting at the centre , assuming a selvidged edge to the cloth , pull with a sickle probe under the pulled trim until the chalk line is right and anchor with surface staple gun. Repeat on finer divisions of each half. Battery covers that are more like secret panels. Inspecting the case shows an area where a cover slides out but no indication of how to release it . Try pressing into this cover at the edge innermost relative to the rest of the box ie furthest end from where the cover slides out. Repairing amps After desoldering the main driver transistors remove all the white thermal zinc oxide paste with cloth or tissues or it gets everwhere, use new paste for replacements. If old and messy to remove just cover with parcel tape , wrapped around. Reinforcing "on-end" large resistor leads to reduce effects of vibration. Feed some QM socket pins on the long lead and solder onto the lead. For small stand-offs for normal mounting cut down and solder on similarly. Broken handle
The type with the spring metal interior and soft
plastic/rubber covering that breaks up
by the metal strap cutting it, and matching
the fittings into frame/ sub-frame is difficult
to find suitable replacement.
Remove the handle and strip off the plastic.
Wind on some spiral wrap cable sleeving from
the slot at one end to the slot at the other.
Shown de-twisted between 2 molegrips on the
cabinet. The card under the handle is just for
contrast in the pic.
Cover with some heatshrink and heat so the wave
of wrap appears and repeat for extra strength.
The ripples giving a bit more sureness of grip.
The metal ribbon will have difficulty
cutting through the nylon
Thats what I've done before and bits of desolder braid and stripped coax
shielding and also scraping back board/trace lacquer for more contact area
and folding back leads along traces before soldering.
Eventually found a hobby shop with what I was after
2 copper and 2 brass 80 mesh 5 x 6 inch sheets, bit finer than I was after
but finer is better than coarser.
Amaco of Indianapolis , Wireform Metal Mesh and Wiremesh woven Fabric.
Presumably bigger sheets of it are used by the mind control nutters.
A 2 hole paper punch makes neat 5mm pads and a needle to make a pilot hole.
While there I could not resist a bag of miniature wooden 3/4 inch long
sprung clothes pegs by Artstraws ,Swansea, for holding small bits while
soldering or gluing, as I use the full size traditional wooden ones for so
many things , including broken apart for wedges.
Spectacles and electronic repair.
If your specs have metal side-arms then cover with some
small diameter heatshrink tubing before they fall off in
some kit.
Reinforcing failed solder pads
Reinforcing solder points on dropper resistors, subjected to
vibration. Forcing a small pad of mesh over the lead and burying in the
solder.
My local decent hardware shop has nothing , a local machine mart has
expanded brass sheet but that is too coarse.
I have used desoplder braid before and stripped coax shielding but they are both messy
for cutting small pads and also pushing mesh over the leads would give a bit
of mechanical grip even without any solder.
For large pads I've also used cut down and cleaned up old perforated zinc as
used in old larders for ventilation but keeping flies out. It seems to
solder quite well but its a bit thick for most components
I can only assume I will see more and more of these bad joints due to
lead-free soldering.
Recently I returned a Marshall valvestate to its owner.
I had previously, last year , had to reinforce solder the main caps, which
is common enough with leaded solder in combos. At that time I did not
realise it was probably lead-free soldering especially as made 1998.
This time 5 different medium size components had bad solder.
Including one I've never seen from normal use rather than over-current/
heating. A flat-pack bridge rectifier had one visually obvious bad joint.
I pushed on the adjascent corner with just finger pressure of perhaps 8 to
16 ounces and that pushed through.
I had told him about this lead-free business when he dropped it off.
When he picked it up he said he'd mentioned it to a relative of his who
works for Marconi Aerospace and he was told the same about the problems
they have with it in their area.
There are plenty of industrial suppliers of such mesh by the square m or by
the m but I was after more sample sizing for this purpose.
The pack of hobby "keepsakes & card" making sheets would be enough for 2,000
or so little copper and brass mesh pads.
Now got enough brass and copper cloth to keep me in pads for years but
I will have to be aware of shedding the odd almost hair sized bits of copper
wire fraying off the edges of this cloth - worse than tin whiskers.
Selvidge the edges of these bits of metal "cloth".
Cold testing an amp
Where there has been major damage involving
a lot of components and before daring to power up .
So testing with removed components or new , with
a DVM for "diode" tests etc. Remove the power
supply reservoir caps to stop the probe
voltage slow charging effects from the caps.
Loudspeaker repairs.
Distortion due to voice coil rubbing the slot.
De mount and power up at a suitable frequency.
Just in one position very lightly push the cone radially
outwards and the distortion will get markedly worse.
On the vertically opposite part of the cone stick a bit
of insulating tape pulled and wrapped under the frame,hopefully distortion gone.
Then a thin "wash" of hot-melt glue in half inch strips either
side of the insulation tape over the flexible corrugations.
When cold removed the tape .
The following i have not tried yet tip from someone else. I would
use brass shim rather than feeler guages because of the magnet.
And metal caps may be swaged to the body requiring grinding of
at least one swage point to get access to lever off,covering
cone area to avoid iron filings getting inside.
I have repaired many speakers. Using acetone, unglue the cone at the outer
edge and unglue the voicecoil cap. You will need sets of 4 feeler gauges of
various thicknesses. Put the feeler gauges 90 degrees apart in the voicecoil
gap. Put Glyptol glue between the cone and the outer surround and clamp
using wooden clothespins. Leave for an hour, remove the clothespins and the
gauges, glue the cap back on and reinstall.
I recently did this with a special size speaker in my car for which the
dealer wanted $125. It has worked perfectly ever since.
Bert Christensen, Toronto, Ontario
High power combos that go intermittant
after a period of use. If they use
an elbow jack on the amp to speaker link ,
replace with conventional.
Check the internal construction and if
poor mechanical connection at the elbow means
a resistance and voltage drop, heating the plastic
disc that is all that forces a mechanical connection,
so progressively worsens.
When cold pliers may turn the spindle part but
when heated by current , can turn by use of fingers.
For such a plug that is not too bad, cut a couple of flexible
washers to place under the soldering to the central
pole, in case the following depresses into the casing.
Place a dense rubber pad like a tap washer over
the pin and clamp the cover over the top to
compress down on the central pole.
Elmwood thermal switches.
You won't be able to change the switching temperature
but you can change the function.
ie normally open to normally closed or vice versa.
The metal cylinder part is swagged over a lip on
the bakelite cylinder.
Grind into this swaging on both sides just to break the
grip. Prize back one half of the swaging and separate the two,
beware of small connecting pin dropping out.
Then prize away the locating disc structure.
This exposes the bi-metal dome disc that does the positive
snap action . Simply invert the dome , with the
dome located in the locator part, and replace the heated
end-plate section, re-assemble the bakelite section
and coble together something to wrap around the
swaging part to hold back in place. Dome towards
the switch is cold off, dome away then cold on.
G-V, USA, thermal switches
Old type, linear bimetal, not snap action
dome, can be changed slightly by cutting the epoxy
covering to the exposed adjustment screw and adjusting
by wiring up to meter and placing in a polythene bag in a heated
can of water with a thermometer.
The action can be reversed from normally closed
to normally open but not at the same temperature.
Desolder the can at the juncture. Undo the
adjustment screw so no longer in contact, bend one of the contact
arms towards the wiring end. Turn the 2 can sections
around 180 degree to one another and resolder
or resolder a bit separated to give a higher
trigger temp, but all very suck it and see.
15 thou gap in the contacts gave 50 deg C going s/c
and 46 deg C o/c on cooling for what was originally 100 degC
normally closed.
Opening gap to 26 thou and switching temp was >100
deg C so not very deterministic. Reducing to 18 thou was
70 to 75 degrees.
Oscilloscope Y Amp problems.
For dual channel scopes where there is a problem with one
channel only. Compare DC levels and signals between
good and bad amps like stereo amp problems where one channel
has failed.
Festoon bulbs.
Difficult to find these days for old tuner amp
dial scales etc. If there is space available then
convert high wattage MES screw bulb.
Assuming 1 1/4 in barrel fuse type. Break the glass
of the original or 1 1/4 inch fuse. Solder one end piece
radially to the screw part of the MES. Solder a piece
of silicone or ptfe covered wire to the nib of the MES
and the other end cap to the other end of wire.
Mount the bulb in the lower yoke if vertically mounted.
Patch leads for prototype/test bed
Lost most of the leads with .5mm pins at the end engaging with the
.5mm sockets. 20 thou/ 0.5mm enamelled wire with the ends stripped
back works just as well if careful.
Cleaning nicotine off kit
Use aerosol oven cleaner , test on a small patch first especially for fastness of
lettering/legends/plastics softening. For knobs or cables place in a tray and let the
spray foam up. Wash off residue with methylated spirits and polish up
with furniture polish.
Festoon lamps
Barrel shaped lamps about 1 1/4 inch fuse-size often difficult to find replacements.
The barrels of christmas tree lights are about the same size and come in
a range of voltages, scrape off any varnish. Hacksaw/cut/melt away the plastic housing and
extend one of the wires to make axial.
Coloured lamps
Coat with coloured nail varnish or household varnish mixed with
suitable dyestuff such as artist's oil paint from tubes.
Awkward power tranny to heatsink spring clip
How to remove and replace or even initially place
(without possibly straining the legs of the tranny by lateral forces) such
spring clips as in this 2 angle view
heatsink and spring clip
I slid a thin piece of PTFE sheet between body of tranny and the clip ,
pulled outwards with thin nosed pliers, and then drove the clip along the
slot in the aluminium heatsink, with a punch and hammer to undo, but how to
reassemble. I've slid the clip along the slot (slot profile shows just under
the red "S" on the other heat sink) but not replaced over the tranny for
the pic. It requires pulling and sliding at the same time
The one pictured has space in front to manipulate with perhaps a lever with
2 pins do the double operation of pull in one direction and push
transversely at the same time but its complement is hidden behind some large
caps, so not possible with that one.
Its not possible to just push the top of the clip into the slot as is often
the case with other such spring clips.
The best I can think of so far for clipping or unclipping.
Grease in the slot and a small wedge to the thickness of the transistor laid
to the side of the transistor and a thin covering of PTFA sheet over the
wedge and transistor and lever or push the spring clip
across.
Email reply from the amp maker's engineer
"As to the spring clips, there is no real way of removing and refitting
those, except by sliding them on to the heatsink slots. That can only be
done when loose (no devices
in place ).
Hence, they have to be mounted on to the heatsinks before sliding
them over the devices."
My bit of (clothes line peg) wedge and ptfe sheet method did work but if the
applied force along the slot, is not axial to it then the high-C steel clips
easily dig into the aluminium and jam fast. I found a large pair of
engineers cramps would gradually inch it across, taking up the slack every
few mm , and starting again. Just another thought, with a pair of large
sewing thimbles on opposing finger/thumb you may be able to use enough
finger pressure to slide the clip up the wedge.
But otherwise matter of desoldering the power devices and removing the
heatsink with trannies and then the trannies can be easily slid out from
under the springs.
Fudge to give a bit more life to "scratchy" slider pots without opening up the kit
Indroduce mixture of silicon grease and graphite powder through the front
access slot. Use a hypodermic syringe without needle ,fit a length of small
diameter heatshrink or other thin walled tubing to get the mix down on the
pot track.
Using a digital camera for recording circuit details etc
Using a camera without 'Macro' facility make up a crude mount
to locate another lens over the original lens as a close-up
supplementary lens to focus in closer.
Larger heatshrink diameter required than the layflat
tubing available.
Varies with formulation of the heatshrink.
Very limited final width for this and a pair of diametrically opposite
spout shaped "ears" that will likely not shrink , so not ideal solution.
Say the layflat heatshrink you have then
maximum diameter as it stands is about 44mm.
The final width is limited to about 20mm of
which only 10mm all round will be fully tensioned,
but diameter of about 90mm max. This
is the maximum, smaller than 90mm will
give better final width by choosing smaller ellipse
but still very limited.
With string, pen and 2 drawing pins do the
draw an elipse on paper thing.
Fold in half longways and lay long "diameter" along
the edge of the tubing. So half minor "diameter"
of 35mm and long diameter of 110 mm mark and cut the
tubing with the elipse as a template. Trim up the
remainder of the tubing to give 2 elipses about 35mm apart and
a rough ring of layflat when the residual fold on the
other side is cut. Place the ring around the object
and warm with hot air avoiding the loose part
doubling back on itself rather than towards the object.
Calibrating electronic keyboards.
For a 5 octave keyboard and counting the "white" keys
only the leftmost is probably C then keys number 7
and 14 are C also, 14 is middle C and middle A is the
fifth key above that.
Middle A reading 440.000 +/-
a little on a crystal controlled frequency meter then middle C should read
261.625 +/- a little. If the waveform of the keyboard is not
suitable for the counter then sum the keyboard and isolated
audio generator together and listen on phones
for minimum beats and measure the f of the generator
on the counter.
Dented central dome to speaker cone.
I've not found the ideal solution yet.
Any tame car panel-beaters out there ?.
You know thew ones. A large angular dent in a car body panel and you hand
over some cash and they say turn round a second/ walk round the block. Then
they kick the panel, but they know exactly which spot to kick.
Working speaker but the large perforation-type front grill kicked in or
dropped so it touched the cosmetic dome at the centre of the cone leaving a
number of depressions.
I tried heating with a hot air gun to maybe soften and sucking with a vacuum
cleaner hose - no good.
Tried some dabs of hot-melt in the dents, alowing to cool and pulling in
conjunction with 1 pound weight in some undeformed areas re-created the dome
and then lightly heated with hot air to remove the glue - but didn't cleanly
release and had to dust with toner powder to matt it out - but otherwise a
re-formed dome. Anyone been here before with better ideas. ?
Weights and vacuum cleaner ? Funnel covering all or most
of dome and vacuum ?
Cutting small slots in pcb
Where there is a different footprint for a replacement item and you have to
pierce the pcb, in slightly different positions to the original, to push
pins through.
In actual case ultra-miniature pcb mount toggle switch with thick
pins, not bendable, to go on a populated board. Footprint of 6 pins on
slightly larger , in terms of centre spacings than the original, so cannot ,
without making a jig , drill new holes. The drill would drop into the
original hole. So a matter of short radial slots out to the replacement
positions. Enlarging the existing holes would require filling with glue or
something for structural integrity , after soldering.
Use a small drill bit in a dremmel and use the fluted part
of the drill but its more melting by friction than cutting. I tried grinding
notches around a sewing needle but that did not work.
Dental burrs look like the tool of choise for this.
PTFE string
For tying hot components together enough to stop
any vibration building up eg lines of on-end
emitter resistors.
Start with the thick formulation of plumber's
PTFE tape and twist a cut length and then
stretch it. Not brilliant for tying purposes
as it can still stretch but if the force in
tying is not too great then at least better than nothing.
Maybe if only the thin type then cut 3 lengths ,
separately twist and then counter twist all 3 together and
stretch.
Testing combo amps
Beware if testing with the amp in the cab but
not all retaining screws in place and tightened then
a rattley noise can be from the captive nuts rattling
in the chassis. For general idea of bass
response put a microphone in the input and the
mike near the mains transformer for mains hum.
It is a common failing of combo amps due to long leaded
resistors or capacitors ,usually bulky ones, to resonate
and flex in sympathy with some speaker frequency/power.
If the lead is high coipper content then it work hardens
and fractures, usually at or in the board. Replace with
a larger diameter pin , or remount with a ceremic
bead and a button of that orange silicone rubber salvaged
from the output pressure roller opposite the fuser roller
of a photocopier to take the temperature and
damp any vibration.
Soldering station mod
Where there is a large spring arrangement supporting the
soldering-iron. Surround the spring with a sheet of
expanded metal wire-tied at the rear. It avoids that
all too common problem of unknowingly draping a lead
into the spring and onto the heated element.
Digital camera micro-fiche printing
Assuming the exposure level of your camera goes low enough
it is possible to photograph micro-fiche reader screens and then print
out via pc, use some sort of steady camera mount eg rubber
footed "trivet", like aerial reconaisance photo veiwers.
Toroidal transformers
Needed a replacement doughnut shaped transformer to replace a blown one.
One i had available had been epoxy sealed in the core with screwed inserts for mounting
purposes. The one i required needed to be plain hollow core. The epoxy fill
(at least in this one) was heavily bulked out with chalk or other bulking agent
to reduce cost and was easily "drilled" out sufficient to give clearance
for the original mounting bolt.
Band Amp jig for protecting valves
When working on a power amp outside of its case and of the normal
form with mains transformer at one end and output matching
transformer at the other. Usually leaves one edge exposed and can
easily catch an exposed output valve if the chassis rolls or
you unseeing rest it upended on something.
Assuming the valves don't extend too far.
Aluminium sheet about 20 inches by 5 inches. Bend
down the middle lengthways and place between the
transformers protecting the third corner.
Hold in place with a pair of large cable ties,
or doubled/trebled up smaller ones .
Preferably de-latchable cable ties or make delatchable
by extending the pauls by under-size drilling
and forcing in small nails.
Another simple aid to assist working on large valve amps
a stout cardboard tray from a grocer's shop,
stout enough to hold the inverted weight of a valve
amp while working inside.
Some intermittant problems in equipment are due to problems associated
with spikes coming down the mains line (eg fridge compressors switching on,
washing m/c spin motors cutting in ,arc-welding etc). Some equipment to check for such
susceptabilities . Large transformer or motor with an on-off switch not the proper
swept action mains switch. Problems with timer misfuction where the timing
is taken from mains frequency can be due to spikes from ordinary
room lighting dimmers producing extra spikes interpretted as extra mains cycles.
VCR record sound problems
Checking the 50KHz or so, 30V pk-pk level or so, of bias oscillator at the audio record head
is fine with a scope but the audio component is swamped. Use a crystal earpiece
the sound level would normally be enough to make out normal level conversation
on a TV channel signal input.
Soldering tip
For old components ICs, trannies etc with corroded pins/ leads. Scrape
with a piece of folded fine emery cloth or sand-paper to give a better key when soldering.
And for ICs use emery board nail files either side of each row of pins.
Reconditioning slide switches
Particularly the type of multiway slide switches used as wave change switches in
radios and play/record switches in tape units and function switches in other audio equipt.
Usually impossible to find a replacement
as although the external may look right the internal number of ways and interconnects
is almost certainly different. Especially with old dark brown paxolin boards desoldering
the complete switch often ends in a mess internally to the switch and
to the pcb.. Instead just prize off the metal covering to
expose the slideway. Firstly desolder or burr off the casing pins that go through the pcb. Usually
the bent lugs that grip under the paxolin board inside the switch are inaccessible but
they can usually be bent indirectly when levering off the cover with
only minor damage to the paxolin around the locating recesses.
If the ends of the switch are exposed introduce a screwdriver between the cover and
the slide bar to act as a lever forcing these retaining lugs back enough to release the cover.
Surprisingly the metal always (so far) bends rather than the internal paxolin splitting. If ends not
exposed then grind off part of an end or bend out to get access. After removing the cover bend
back these lugs in line with the sidecasing. Remove carefully so as not to dislodge the moving contacts
too much and note their positions as not always the same size in all positions.
Also beware of dedent spring and ball(s) flying out. If present then for reassembling
use a dab of hotmelt glue on (either) side to retain while assembling and then
with pointed soldering iron melt when reassembled to allow to spring into place if
the dedent has a slot in the metal casing.
Clean corrossion off the line of contacts and the slide contacts and replace
worn/broken contacts from breaking open another switch.
Cut along the length of one or two small nylon cable ties to make 1 or 2 strips of the
right width to slide these sliding contacts onto. Cut down enough to open up the
contact points but leave the nylon recessed enough to give some location when
reassembling. Position the contacts on the nylon to fit the wells in the slide bar of the
switch assuming an interconnecting slot between the wells.
Mix up a paste of graphite and silicon grease and put a dab in each recess in the
slide bar and introduce the line of contacts that are then held within the mix. Carefully invert this bar and
without forcing introduce over the fixed contacts and carefully slide out the nylon to
mate properly. Don't force as a contact may be misplaced. Temporarily fix in
place to turn over and check continuity between contacts. Temporarily replace the cover to fully check continuity
in all positions of the slide. Permanently replace the cover and solder or glue in place.
Lost all those thin bore nozzle extenders for aerosol spray cans ?
Use the plastic bit from a cotton bud.
If too large a diameter, partially melt and
stretch like glass blowing.
Fan inlet filter material.
For coarse filter , to prevent hair and metalic bits of foil or
wire filaments. Use 1 or more of those pads of matted
plastic fibres used for cooking pot scouring.
Also in the kitchen the non-open-weave "J cloths"
the cheaper sort for fine filter cloth in conjunction
with the coarse one on the outside.
Estimating a likely value of a small low voltage polystyrene cap
that has no value printed on it or has melted due to being near a hot R
and foils shorted.
Ground down the ends of a few such caps , stripped the covering off
and unwrapping the foils. 2 foils per strip length L, width W
and separating film thickness d. The voltage rating is related to the value of d
120pF, 22 x 4.5 x .04 mm
220pF, 60 x 4 x .05 mm
680pF, 28 x 4.5 x .015 mm
1800pF, 200 x 5.5 x 0.03 mm
Averaging out gives an approximate fomula of
Capacity in pF approximately , dimensions in mm
C = 0.0487 x L x W / d
Some tips for repairing switch-mode power supplies.
For personal safety use a RCCD or ELCB ( trips out when there
is a leakage from supply to ground) which should of course be in line
to any repair shop work bench. Also a variac supply and a 1:1 fully
isolating transformer for working on
switch modes. Disconnected from their loads these s/m supplies will usually
kick in and maintain operation at half mains voltage,safer to work on and
also less stress on any overloaded components.
Unless it is absolutely necessary don't use a scope when checking /repairing
unknown s/m power supplies. To check whether the oscillator is driving the principle
transformer use a small "sniffer" a mH small choke connected to the lowest ac V range
of a DVM. Although not designed to monitor 40KHz - 50KHz signals it will register
a few millivolts if osc. operating and magnetically close coupled. This "sniffer" will also pick up
induced voltage from TV degausing coils for checking. For cold checking circuitry connected to the principle
transformer of a s/m supply use an ac inductance meter rather than resistance DVM to
distinguish coil inductance from "zero" inductance of shorted diodes,electrolytics etc.
White ink pen for marking info on black plastic IC bodies
I've not found the ideal solution yet - Staedler or Stanger
permanent ink felt tip pens with white ink yet.
In the UK gel pens by Mitsubishi Pencil Co are half way there.
The bright pink one is good colour contrast and will write fine lines on
black plastic. If you allow a day for it to dry then it is reasonably fast,
you have to rub it firmly before the dried gel will rub off.
Asda own brand metallic felt tip pens are contrasty to black.
Gold or silver , more permanent than gel, but you'll
have to sharpen the points with a razor blade for writing on ICs
Small scale vacuum forming machine.
From a de-solder vacuum pump , 2 oz tobacco tin,
polythene tube, rubber sheet and a hot air gun. From what i remember of
radiant heated sheet, vacuum forming machines, they could do with an adjunct
of hand assisted hot air because of cold spots or tight radii.
Trying to make a keypad covering as used in bars and restaurants
to keep crud off the keys
Tried doming out in the button positions some expanded ali sheet as a mould
, did a superb job of giving a diamond patterned surface of the plain sheet
and blisters formed but were not large enough or deep enough. Will have to
try step-repeat drilling out some metal sheet with larger holes than the
original front panel and some backing of expanded ali as an internal stop
face.
Tip for equipment used in schools/colleges/universities.
A slide projector kept blowing bulbs far quicker (perhaps within a half hour) than
should be the case. Class finished early in each case. Someone eventually noticed a student must have moved
the voltage selector switch from 240V to 210V . If he had set it on 110V it would
have been immediately noticed something grossly wrong. Once in a while there is a clever student.
Moral for
equipment permanently used in a 240V environment and in proximity with students
disable internally the movement of these switches.
Rough data for anyone making a contact type moisture content meter.
From a Tramex analogue meter.
3V pk-pk ( across basic 1:1 scope probe) sine, 12 KHz signal between
2 conductive pads. 3 scales: 1 Timber , 2 Felt roofing, 3 Plaster/brick
Resistors placed on some expanded polystyrene and
meter pads pushed against it
100M Ohm Scale 1 9%, 2 30%, 3 1%
10M 12%, 46%, 1%
1M 64%, >100, 2%
100K >100%, >100%, 38%
10K >100%, >100% , 50%
Scales 2 and 3 0 to 100%
Scale 1 (timber) same movement but marked <10 to 20%
reading 14(scale 1) corresponds to 30% (2&3)
16corresponds to 62%
18 " " 83%
Source of small storage containers.
Film processing shops usually throw out the small plastic tube pots that 35mm
films come in, use for storing components. Can also be used for in-line housings for filters,adaptors etc. Another
source of small cases is hospitals that throw out the plastic boxes that suture needles
come in.
Reconditioning old style open 1/4 inch jack sockets
Weakened metal on the U of these open sockets
so not making reliable contact.
Open out the U so the V tip of the contact is in line with
the V tip of a plug.
Tie tightly a cable tie around the curved section to reinforce.
No point in replacing
these with modern ones as will be weaker anyway.
Making up high wattage zeners.
Needed a 13V,5 watt zener. Had some 5.6V ,5W zeners so 2 of these in series with
2 1N4001 gave 13V at the required current.Beware of "different" polarities (band marks) though.
Testing loudspeakers.
Particularly for owners to check their speaker/speaker connections where
it is possible a short has blown the amp and they are non-technical and no
meters and you don't want a bouncing amp repair job.. With a charged 1.2V ni-cad
touch the 2 leads to each speaker to the nicad and you
should hear a thump from the speaker if OK. Also useful for checking
possible reversed polarity wiring to the speakers. Touching similar sense wires
to the ni-cad should pull in the cone in both cases or push out in both cases. If you
can't see the cone then thin paper over the grille should indicate the punch of air
or push a thin piece of wire up against the cone (don't hold tightly)
Sacrificial power trannies for audio amp testing.
To save destroying expensive TOP3 package or even more expensive
widened 2 hole fixing "wide TOP3" trannies use a 2N3055 or 2N2955 (for pnp) adapted
when checking out a blown amp.
From a TO3 heatsink ,the type with the trannie sitting diagonally and turned up
cut vanes on each of the four sides hacksaw off the vanes and also saw a slot into
the 2 "B and E" holes. Solder silicone covered wires to B and E close to body and
file back surplus. Solder another wire to the case and mount using
the cut down heatsink as spacer and the usual usual insulators
to the heatsink of the amp under investigation ,just one hole fixing will do for testing
purposes. Incidentally a lot of the time (don't tell the hi-fi purists) pair of TIP3055
and TIP2955 will replace the rarer complimentary pairs of trannies for non critical
replacements. Perhaps with one-hole fixing only and skewed mounting.
For higher current (25A) there are TIP35C and TIP36C.
For TO220 package situations use TIP41C and TIP42C and
for higher current situations BD911 and BD912
Making a board extender.
Working on a piece of old digital equipment with numerous PCBs off the one
back plane. To monitor ICs had to make a board extender. Finding a double
sided card edge connector was easy enough but no "male" connector available for
the other end. If too many ways to the female connector plug the surplus ways
with a bit of blank board to prevent mis-registering the "card extender"
Cut the gold-plated edge connector off an old board leaving enough track to
each land to be able to abraid back and solder ribbon cable to. Solder one
side of the ribbon cable to this set of edge contacts and with a hot melt glue gun
glue a piece of blank PCB abutting this set of contacts. Solder second side of
contacts and hot melt glue in place. Gives something to purchase on when introducing
and extracting the "card" extender. High frequency working with such a "board" without
ground plane would probably lead to anomalies.
"worn" pot tracks
Specificaly compound dual pots where there is a problem with the "middle" pot
that cannot be accessed internally without destroying the other pot. Recently
came across a custom dual wire wound ,log C-law winding,pot in bakelite casing but probably
applies also to tin-plate casing as well. In the area where the 3 terminals protrude
through the casing and in the direction away from the pot track cut into the casing
with Dremmel and cutting wheel or ball mill to gain some access. Squirt in
methylated spirits to expel swarf etc. Soak in meths to soften any deposits and
dislodge with cotton wool bud etc. Then coat with silicon grease/graphite mix.
1 inch, low current, fuses
As used in some Solartron equipment
Break a mains or 1 1/4 one and solder the end caps to a 20mm one
Marconi test equipment of the 1970s.
Problems with double sided PCBs and the thru' board via connections leading to intermittant
and regular function failures. Resolder all such thru' board points as they are not visibly
"dry joints"
Breaks in cables including co-ax cable.
Use a needle point (described elsewhere) to pierce the outer (and braiding of co-ax)
to pick up the core and use a continuity checker. Breaks are often near the end at the
connector ;so can cut back perhaps a few inches and reuse the rest of the cable .
Waggle the needle in a bit of dowel around to move the screening out of the way a bit to engage only the core.
Earth's magnetic field tilt on oscilloscope displays.
If the DC coil round the CRT has a break use a small magnet mounted with velcro
to a pad glued near the front of the CRT and adjust to suit. Gives slightly curved
traces but usually adequte for readings at centre of display.
IC protector for monitoring IC voltages to avoid the situation of the 'scope
probe or DVM probe accidently bridging adjascent pins. Cut down the outer plastic
casing of a linear connector (like Harwin type) with matching pitch and temporarily place between the
pins of the IC.
Irreversible Thermochromic materials/chemicals
Commercial thermochromic labels seem to have very
restricted ranges, large physical size and expensive for
what they are. Confirm that your sources
agree with these below.
If anyone can add to the following list of useable
materials please email me.
Painted, perhaps mixed with light coloured dye to
distinguish active side, onto paper , dried , rolled
up, flattened and fed through an ordinary paper punch
for small dots to fix with gummy glue to whatever.
Thermal paper for fax machines or till rolls (the material
I had turned blue) stained to show active surface
changed colour about 70 degree C
Potassium dichromate, a weak solution giving
a light yellow tint, turns light brown
at 85 deg, mid brown 95 deg, dark brown at
130 degree but go higher then goes grey on cooling
so beware.
Photocopier toner fuses about 90 degree C but
could not thing of a way of using it for labels.
Mylar film (or metalised plastic anyway)
bubbles/wrinkles 75 deg , shrinks
80 degree and shrunk to 1/4 95 deg.
Hot-melt glue, formerd into strings, cut up
to cylinders. The one I tested changed cylinder
form at about 105 deg C so melt one surface
with soldering iron and adhere to monitored surface.
Fluorescent paper looses flouresence at 100 deg C
Liquidised red cabbage, room temp ,
light blue/grey, goes definite grey at 110 deg
and brown at 150 deg
Gardeners Cheshunt compound , mixture of copper
sulphate and ammonium carbonate goes from
pale blue to light brown at 135 deg
Plain white soap rubbed onto paper
goes brown at 160 deg C
Some commercial stationary supplier sticky
dot labels, all stayed colour fast to 200
degree C except the dark blue that turned very dark
blue at 200 deg.
Poor man's strobe.
Connect an ordinary LED to the output of an ordinary square wave audio generator.
Assuming enough current to drive an LED also if much larger than 2V pk-pk put
a suitable dropper in series with the LED.Subdued room lighting is required to observe
stobe action with spinning shaft ,pulley,video head drum etc.A frequency counter
attached also to the sig. gen. will give exact frequency.
Put at least one index mark (gummed label, reflective glass bead tape etc) on the rotating item.
Usable with a general purpose LED up to fairly high rotation rates.
To check for constancy of rotation of a vcr head drum you may have to observe at
a lower "sub-harmonic" of the line frequency as an ordinary LED may not function
at these frequencies.
BA screws/bolts/nuts in the USA and UNC/UNF in the UK
For just the odd missing screws/bolts situation.
It looks like the solution to this problem is someone in the UK to tie up
with someone in the USA and a packet of assorted small size UNC/UNF nuts and
bolts go surface mail one way and a packet of various small size BA mainly /
mm nuts and bolts goes back the other.
The commonly used sizes for electronic kit in the USA
are 4x40, 6x32, 8x32, 10x32 and rarely 10x24
screws.
In the UK 2.5, 3 and 4 mm and 6 BA and 4 BA.
Cabinet hardware being larger sizes.
Now where the !*~! did I put that
Anyone else, like me, remembers exactly where something was originally. Then
it gets to the stage where you have to have a tidy-up and now buggered if
you can think where you put it in the much more recent past. I'm aware of
this fact of life and I try move things to themed areas if possible. But it
still fails, my idea of themes perhaps change.
I think the main problem is using the item from its new place of storage and
just not returning it there but somewhere else or just to the ever
accumalating heap of assorted kit around the work area until that area has
to be attacked.
See the "volcano" principle of desk-top management - you allow papers to
build up and up knowing that if you don't disturb things then everything is
in chronological order of when it was placed there - until it gets to the
stage of "larva" of cascading flows of papers onto the floor when something
has to be done about it.
I think I'll invest in some sheets of those little bright circular paper
sticker dots. Then a 3 or 4 dot system.
First dot , one colour , for each room or shed , garage etc.
second dot - for each bay or cubboard has a different colour in that room
third dot , different colour ,for each shelf in that bay
fourth dot for small items within one box on a shelf all one colour
Even computer recording stuff would only show where things should be ,
rather than where they actually are - perhaps one day everything will have
RFIDs and problem solved.
A problem i find is the "in progress" repairs. Kit that is opened up ,
trouble diagnnosed , but a replacement part has to be ordered and delivered.
There is no point in putting all back together only to taake it apart again
when the part arrives. So manual , specialist tools, meters etc relating to
that job, that would normally live elsewhere, have to be associated
together until job complete, hopefully.
On a related theme - for a large collection of paper-bound manuals or data
sheets.
Never pull a manual without replacing its position with a coloured piece of
filing card as its so easy to either not replace it in the stack or replace
it in the wrong place, and then effectively lost until you spy something out
of alphabetical order , years later.
Thermal switch of make T'-key, T-'key, T'key,4key, T?key ?
Bimetal dome, snap action, switch .
Google has failed for this one, other
than another failed usenet enquiry
Marked T220, so at first sight looks like the temperature
but is it centigrade or fahrenheit?
and 10 amp /250V or 15A/120 V
Other markings
C1-2026 ?
125-a15 ?
07A15 ?
not too clear ink-jetted markings
looking under a low power microscope the logo is probably
T'-key with the ' over the - symbol
did find some images though
http://mysite.verizon.net/vze1otp1/Ebay/122fthermalswitch1.jpg
http://mysite.verizon.net/vze1otp1/Ebay/122fthermalswitch3.jpg
those are also mould marked T220, but those are apparently 122F
Ebay is useful sometimes
I've not found any T'-key company site but with those Ebay ones being 122F
with product code 050-15 and 50C = 122F
The one I have the middle code is 125-?15 so probably 125 degrees C = 257F.
This one I took to 120 degree C without it changing state.
Other Thermal Switches of type with logo of
C followed by 2 square wave pulses
KSD301
K85 probably (smudged)
Checking in a can of water and it goes s/c at 86 degrees C
and reverts to Normaly Open at 71 deg C
So the 85 means 85 deg C and perhaps K means NO
Dealing with foil ribbon cables.
That is the thin cables 1mm or .05 inch spacing with conductor ends that mate with small pcb "edge connectors".
Often white with small blue reinforcement at the open ends or phenolic brown in colour.
Before replacing these ribbons in their sockets bind some upholstery sticky tape a few times
around each end overlapping the small plastic reinforcement strip if present to give a much firmer
end to avoid buckling and cracking the foil conductors on reinsertion.
Making audio tape recordings of uninterupted 4 hours or more.
Use a standard vcr with external audio and video baseband 1V inputs.
You need a video source from some external source eg other vcr,video camera
etc. Feed this in video-in to let the syncs pull the servo system down
to the correct speed. Feed the audio mono or stereo from tuner,microphone/s etc into the vcr
switched to external input. A vcr with long play option could increase
the recording length to 8 hours in one uninterupted run. Use the vcr timed
record to record at preset time.
Salvaging the copper and iron from large transformers.
For obvious reasons not for sealed transformers or
the ones that contain oil.
When having a garden bonfire of brushwood cook them in the
bonfire. This burns off the cloth, paxolin, varnish from the wire
and more importantly from the iron "E" and "I" plates, also
makes undoing the bolts easier (when cooled of course).
I suppose because of the heatsinking of all the bulk
of metal the flames do no turn green, presumably only occurs
if the copper gets a lot hotter.
Undo the bolts, hammer the iron slantways to break any
remaining stiction. Ratio of retrieved metals would be something
like 1Kg copper to 3.5Kg iron
Repairman's knot
I started a usenet thread enquiring about the
knot for tidying up the mains lead of equipment.
I was aware of an ex-services variant where the
plug is jammed up against the cable entry point
into the kit and everything is so tight that you need
a screwdriver to priize the knot apart.
Mine is a bastardised version of this much more
elegant one courtesy of "Arfa Daily"
"Assuming that you are right handed. Zig-zag the
cable in your left hand, starting up close to the equipment, and making the
zig-zags about 8 inches. Make about 5 or 6 of them, which should have used
up about 1/2 to 2/3 of a 'normal' cable length. Stop zig-zagging when the
cable end, with plugtop, is away from you. Now take the remaining cable in
your right hand, holding it close to where the zig-zagged piece is hanging
out from your left fist, and take a single tightly pulled turn around the
end, winding away from yourself. As you complete that first turn, angle the
cable in towards your left hand, so that it crosses over the point where
that first turn started from. This locks the turn in place, and now you can
just go ahead and keep winding the spare cable around, feeding the
zig-zagged piece out of your fist, as you go. If you've judged it right (
years of practice ! ) You should get about 11/2 inches from the equipment
end of the zigzags, when you have about 6 or 8 inches of cable left. This
last piece of cable is formed into a squashed loop, and fed through the end
loops of the zig-zags. It is then pulled back over the zig-zag loops, and
finally, you pull on the plugtop, which pulls the last loop in nice and
tight. This method is the neatest I've ever seen, and NEVER comes undone on
its own, unlike attempts that I've seen many engineers make, to reproduce
something similar. Where they usually go wrong, is wrapping in the same
direction as they made the zig-zags, This fails to lock that first turn in
place, so the whole wrap becomes loose and sloppy. It's a lot easier to do
than describe, but if this is the standard old repairman's wrap that you
were looking for, I'm sure it will come right back to you as soon as you try
to follow this."
http://www.nbndesign.com/stuff/Wirewrap1%20end%20result_320x240.jpg
http://www.nbndesign.com/stuff/Wirewrap2%20first%20turn_320x240.jpg
http://www.nbndesign.com/stuff/Wirewrap3%20all%20turns%20in%20place_320x240.jpg
http://www.nbndesign.com/stuff/Wirewrap4%20loop%20fed%20thru_320x240.jpg
http://www.nbndesign.com/stuff/Wirewrap5%20loop%20pulled%20over_320x240.jpg
http://www.nbndesign.com/stuff/Wirewrap6%20endgame_320x240.jpg
Opening TV/VCR remote control/zapper cases.
The best tool for opening the snapped together 2 part cases found
in such items is the human fingernail attached to finger. The chittin?
has just the right amount of strength,rigidity and flexibility to get into
the gap and bend into and separate the parts held by the nibs.
To help determine which part of the cover separates from the
other, carefully squash in a vice. If a gap emerges try old
credit card plastic in the gap, screwdrivers will always scuff
the edges.
Amps etc with falsely triggering protection circuitry.
Assuming the main + and - rails are balanced.
If you are loathe to disable the protection cct
before powering up with a variac then cut
the lines to the main +- supply rails and insert a
diode first in one rail and power up. If
still triggering remove and try the other rail.
Often the cause is drift and falsely saying
the main rails are not balanced.
If not discovered like that or another cause
then its a matter of disabling the protection
relay/s and powering up via a variac from
a low beginning and watch for problems.
PCB track layout to schematic conversion
Capturing the track layout on polyester pcb - hold
white card laid 45 degrees to the component side and illuminating the card
with a bright light, masking off around the board with opaque card.
Photographing and then greyscaling and upping the contrast, loses the small
component shadows. Broaden or widen to fit the page to give more room
for overlaying components. Giving a very usefull track layout with a bit of manual
touching up for big component shadows etc in full colour before greying
and upping contrast . For paxolin boards illuminate with a linear fluourescent
lamp at the best angle for greatest contrast.
Other photos for resistor values and overall views plus manually recording
overlay numbers that are hidden, transistor types, capacitor values etc.
Print off a mirror version of the tracks so you can lay the components
over the top as if the pcb is absent.
Now the fun bit, it would be nice to expose, onto rubber sheet, pcb etch
fashion. Mark node numbers and stretch into straight lines the DC rails and
one or more other major lines and then manually cut and bridge or whatever
for first stage schematicing.
Anyone know of a pc application that does this stretching of a digitised
image under human control.
cut-down example without any manual retouching of the photo stage
http://www.diversed.fsnet.co.uk/pcb1.jpg
http://www.diversed.fsnet.co.uk/pcb2.jpg
http://www.diversed.fsnet.co.uk/pcb3.jpg
Better than sudoku.
Is there a general guidance for human only layout to schematic conversion
anywhere out there? I tend to start with DC rails but then what. I imagine
the numbering sequence for Rs and Cs should give a broad area of where to
plonk them in the final schematic but a thin infinitely extendable rubber
matrix would be nice.
Deformed hinged plastic switch covers on VCR front panels
Where there is a machine malfunction but the owner thinks pressing the
switch ever harder will make it function. That is where they have pressed
it so much that its permanently wedged in the gap between face plate and
pcb. On demounting the hinge plastic although not broken is permanently
deformed resting on the switch button. Temporarily hold back the cover
in its proper retracted rest position and glue with hot-melt glue 2
small lengths cut off a nylon cable tie,well bonded in at either end on
either side of the hinge.
Removing QM pins from their housings to re-use the housing.
Especially the female pins. Make up two tools consisting of a steel tube with a file handle
fitted to the end. Both made from tube turned at least at the active end to 2.5mm internal
diameter and <4.1mm external. On one of these relieve the internal end surface into a bevel .
Use this one first to reform the pin back enough to allow clearance of the other tool
to push over the pin to the holding matrix to release the "spring" and can then be
pulled out from the other side.
Updated , much simpler tool for QM or Molex - for electrical SOCKET pin extraction
Start with a 4mm babana plug. Push a point in the banana bit , bend
outwards and pull out. With a 2.7mm or near size bit, drill into
the shaft about 10mm to open out. Then a 3.1mm or so bit , a few mm
in to form a lead in. File away the internal ledge with a needle file.
Even simpler tool for QM or Molex - for electrical PLUG pin extraction
Start again with a banana plug and remove the "banana" - thats it,
nothing more, the perfect tool for pushing out the male type pins.
For reconditioning poor contacts , the extraction process
closes the socket up a bit, also re-crimp the wire
connections when removed and clean contact surfaces.
Adjusting IF / RF coils
For people who want to take a chance improving radio reception where the
radio basically works but over time the decoding of stereo only works on
the strongest signal or improve the gain perhaps. Where you don't have the
relevant test gear or info to properly align. Measure the depth of the IF slugs
from the top of the cans. Unfortunately the depth mic part of vernier callipers
and dedicated depth micrometers are too broad to go inside IF coils. Make up
few of the following. Get some long bolts or studding and matching brass nuts.
Solder a brass washer to a nut to make larger for each depth guage. Mark I,II,III
etc . Put the studding in the recess, wind down the washered nut until touching the
top of the can and screw down a lock nut,just finger tight. Mark the cans I,II,II
etc and position of slot on each can. Remove the guages and fiddle to heart's
content knowing at least you can get back to your starting position.
Drifting out roll pins that retain pulleys on shafts.
That is the very small pins through small shafts. Even if you have a pin punch
of small enough diameter it is very easy to shatter the high carbon steel
pins of the smallest punches. Use a pop-rivet (blind tension rivet) the pins
on these are fairly high carbon and if bent no great loss,grind the exposed end flat
as they are often snip-cut.
How to make a high magnification binocular magnifier.
That is the sort of magnifier used by surgeons to do intricate surgery while
keeping their head out of the way. The professional kit looks like small opera
glasses fixed to their forhead and costs an arm and a leg. I am often finding with small electronic
kit these days that there is not
enough room between my head and the piece i am working on to leave space
for magnifier/spectacles ,illumination and soldering iron or other tool. Working on SM boards
with components surrounded by larger components means the soldering iron has
to be used almost vertical so just no room to work under magnification. The following looks
ridiculous but who cares.
The main requirement is 6 small plastic magnifiers. The ones i had were front of hobbyist
magazine giveaway plastic pocket magnifiers with plastic lenses. Otherwise similar
very basic magnifiers would probably be in toy or hobby/passtime shops or even
nickel and dime stores.The ones i had to hand were 10mm diameter
lenses of 55 mm focal length but 15mm diameter would probably be better.Standard plastic
"Sherlock Holmes" large types would have to be cut down to 15mm ,even sawn square
would do, to be manageable.
Make 2 off of the following. Stick 2 lenses close together,in this case 6mm apart
and mount in a cardboard tube (for the lenses i had ) 90mm long or whatever length to bring
into focus. Mount one ,with doubled lens nearest,centrally
to each eye (which may not be the centre of the specs) on a pair of plain plastic
lens safety spectacles . Glue a ring of plastic to the specs to locate the end of the
compound lens barrel. Then with 3 or 4 cut down cable ties glue the barrel to the edge
of the specs. Cut off the catch end off each tie and mount other way about so
only relying on friction and not the tooth/rack part of the clips. This allows adjustment
of the pointing of the barrel essential if using 2 such barrels and full binocular
viewing. Also fix some strong elasticated cord to the specs to go around the head as
the extra weight will pull the specs out of eye alignment and soft tape on the nose bridge piece if
rather angular.
The image is upside down and somewhat distorted
off axis but for my lenses gave a x8 magnification and 200mm of clear space between the
workpiece and the first lenses and a whopping 300 mm between my own head and workpiece.
Paint the surrounding part of the safety specs with black paint to reduce the distractions.
I gave up making a binocular viewer settling on a monacular . It seems almost impossible
with this sort of magnification to get the centre of each eye on axis with the barrels and
zeroed in on the same spot for binocular viewing.
Professional ones presumably have pentaprisms and mirrors to give right-way-up image
and reduced front to back length .
Lost mains leads on old equipment with obsolete connectors.
Often seen with the linear type connectors found on Telequipment
scopes but any other old equipment can have the same problem.Remove
the original socket and replace with an IEC or smaller cassette
lead connector if space is a premium but beware earthing ,3 wire, is
often required.
Radio dial cords and tape drive belts repair.
Tune into a familiar station.
Before dissassembling, with a felt pen mark across the cord and main pulley
attached to the air-vane tuner capacitor, also mark the path of the cord around
pillars and pulleys and position of dial indicator.For complex cassette tape drive paths
do the same.
Removing those black plastic cord grips for mains leads
That is the through chassis grips in two parts a major and minor
part fitting through a hole with 2 flat sides. Use mole grips (lock-
jaw pliers) to compress the 2 parts to give enough leeway to remove. Also
useful for placing/replacing these cord grips.
To remove the more awkward circlips
The type are relatively thick with no gap between clip and spindle and
have sickle shaped open ends.From a set of cheap jewellers screwdrivers find
one that is just bigger than the gap between the 2 V notches in the open ends.
If the circlip is bearing against a rigid surface slightly round the edges of the screwdriver
and force into this gap and the clip usually comes away and leave held on the screwdriver
for later replacement.For free standing clips back the clip with some pliers or suchlike.
An improvement on the pencil graphite on worn potentiometer track trick.
For pots that are worn and it is not possible to replace or adjust the sliders to
an unworn part of track. Often seen as the slider pots on cheap stereo units.
Make up a paste of one part silica gel (silicone grease) to one part of powdered graphite (from locksmiths /
hardware stores for locks as dry lubricant) into a paste and smear onto the track.
Packing fragile items for the postal system.
As well as bubble-wrap inside cardboard boxes consider
the following. Save pint or 2 pint plastic blow-moulded
milk cartons. Clean out and dry with cap off. Replace the
cap and use as packing inside a larger cardboard box than
you would otherwise use. One on each face acts like
car air bags or even Martian lander. Perhaps part fill each bottle
with polystyrene chips in case the bottle bursts
in a heavy bump. If the gap is too small then release cap
and squash a bit before replacing cap. Tape in place
around previously bubble-wrapped item. I sent an old bakelite
cased meter to Italy using this technique. It already had a known
crack in the casing and didn't worsen in the journey - which is
some testament for the technique.
Another tip - some packaging that small domestic electronic items
are delivered in can be unfolded and folded back with outside,
with printing on, becoming the inside and plain on outside for re-using
Stringing parcels to form a handle
Cut sufficient heavy duty string. Form a bowline or
a loop at one end. Place the free end of the loop on the top
of the box about 2 inches from one end (longways) , pass
around (shortways) and up and through the loop then back
down over the end , under and back up the other side.
Hold a right angle on the top , same position from the end as
the first loop end. Go round shortways and back about
this angle and close across the top , tying-off and
loose the escess tring by repeatedly going back and forth
this central top section to form a handle.
Using a wheelie bin for parcel delivery drop-box whan absent.
Preferably a recycling bin as generally cleaner.
Fix the main handles to a screw-eye fixed in a post or wall
using a chain or wire and padlock. To avoid the dustmen
taking it away if they collect on the non-appointed day, mainly.
Pack out with boxes or something so not too much a drop.
Find a car "crook lock" to hook one end around the
wheel/axle (may need hook opening out a bit).
Then another padlock and wire or chain to form a loop
through a top lid handle and the top hook of the crook
lock and adjust the length and lock off the crook lock to
that length. Open the top lock/chain/wire and leave
open for parcel deliverer to close off. That padlock must be able
to be closed and locked without use of a key.
Converting D or O section potentiometer shaft to spline type.
This situation arises on amplifiers etc where one pot needs replacing and all the
knobs match but have splined shafts and the only type of replacement pot you can find
is D or O in cross-section.Find a sharp screw-threading tap (for cutting screw threads
into bulk metal ) of about 1mm pitch.Cut the
D section shaft of the replacement pot down to the required length.With a scraping
action using the cutting edge of the tap (along the flutes of the tap) scratch grooves
axially along the pot shaft.You don't need to be accurate,in practise enough scored
grooves will engage with the knob and hold even if the back-torque of a combined
switch action is involved integral to the pot.With a hacksaw cut a slot part-way
down the shaft ,axially , and perpendicular to the flat of the D.If the knob is too tight
then increase the length of the slot.
Dealing with short-circuit Ni-Cads
Treat each cell seperately but it is not necessary to break up packs,only strip back
enough covering on each cell to gain electrical contact.Find a large electrolytic
capacitor something like 20,000uF,80V and connect to a supply with ordinary hook-up
wire giving 70V at .5Amp say,the power supply must be able to survive a
short-circuit on its output so use a dropper if this is not the case.From
the screw terminals of the capacitor run two thick wires,cooker cable or car
jump start leads to discharge through the short in the ni-cad.This will only
work on dendrited cells that is where a thin whisker or whiskers of metal grow
to bridge the plates,more extensive internal shorts will remain.Fast charged
cells that develop shorts would appear to be due more often from internal
dimensional changes and plate to plate contact.When discharging avoid looking
at the blue flash and possible arc-eye.A high current can pass for a short
duration but not enough energy to explosively heat up the cell should the
discharge wires/clips weld to the case of the ni-cad.Ni-cads that have
chemically broken down,that cannot pass current and have terminal voltages
substantially above 1.4V on charging can only be cut out and replaced.Beware
of the white powder found on such Ni-cads as this is poisonous so wear latex
gloves/wash hands after handling such cells.
Cheap and cheerful rubber drive belts
Whenever you go past a cycle repair shop,a motor-cycle
repair shop and a car/commercial vehicle tyre fitting company go in
and ask for a scrapped inner-tube.For tape players a range of tubes
from moped to big motor bike suit best. From a collection ranging in size
from high performance racing cycle to lorry tyre it is possible to cut a good range
of belts. To increase the range it is often possible to make diagonal cuts
across the tube to give longer belts but residual "twist" in the belt
can cause riding up and down on "baluster" bulbous pulleys but fine
on plain cylinder type pulleys. I've not tried this yet but it might work.
From a slab of lorry inner tube cut an oversize belt and tidy up
using the "been slicer" technique of the next tip using a couple of
spaced razor blades.
How to split rubber drive belts that are too wide or thick
In conjunction with the above tip.
Need a razor blade and pairs of thin washers or spacers and
an engineers parallel jawed clamp.
Find washers and razor blade combined thickness just less
than the thickness of the rubber.Set razor sandwiched by washers
in the tightened jaws of the clamp with the
cutting edge a few mm protruding at a reasonable cutting
rake angle.Carefully make an initial cut and then pull
through the length of the belt.Repeat for quartering a
square section belt.
For bands made from lorry inner tubes the rubber is too thick for
the bands required for vinyl record decks and the like but they can
be halved or even thirded in thickness after some practise.
Cut across the inner tube and place a tub or something inside to pack-out .
Cut some vinyl tape of the right length (usually smaller than the original
band length) also reduced about 3 percent as the following splitting process seams
to lengthen the belt. Wrap around the tube usually diagonally making
a good line with both ends touching sticking to the tube. Crudely cut from the remainder.
Clamp to a board with cramps a thick metal plate with sandpaper glued on
one face to stop the rubber slipping when cutting. Cut about 1/3 of the
circumference at a time with craft-knife to give band of right width.
Pare away any original moulding streaks on the rubber
Select 4 washers of the right thickness so 2 plus the width
of a pointed scalpel blade is just less than the thickness of the rubber.
With hot melt glue bond 2 washers either side on the wide end of the blade.
Do same on pointed end ,cut away any excess glue so can mount in a clamp and remove the washer
assembly from the pointed end so can pass through the rubber after initial piercing.
Clamp rubber between some small blocks around 3 sides and
with a needle point push thru halfway on the narrow edge then reverse and repeat on the other side.
Then with a scalpel blade push in both ways round on one side then repeat on the other
side. Refix the washer assembly and clamp in an engineers clamp and mount
this in a vice with the scalpel cutting edge angled to give a good cutting angle
to the rubber . Then with leather gloves and goggles in case the blade should pull out.
Pull the rubber through splitting in 2. The skill is constant tension on the lead and
a lesser tension on the tail to give an even thickness of cut. The cut surfaces
tend to bind to one another so when finished and parted coat in talcum powder.
Typical result for a 5mm wide band ,1.5 mm thick is an extension characteristic (one section)
when pulled of 110 percent elongation per Kg. The end result is unlikely
to be as uniform in section as a manufactured belt but the acid test is on a
record deck with strobe. Probably because although the extension in different parts
of the belt vary ,the tension in the belt is the same. Anyway these belts seem to pass
the strobe test. Use the belt with cut surface away from the pulleys as tends to be rippled .
For cheap plastic (no inertia) plattens on cheap music systems
it may be different matter.
Making defunct CRTs safe
To release the vacuum inside a CRT. Remove the multipole connector from the
neck of the tube and at the centre usually is the point where the air is
evacuated originally and is usually the weakest point.Take outdoors and place
CRT-face down on cardboard or similar on the ground and
cover the whole CRT with something like the composite back pannel
off the TV with just the centre of the CRT neck exposed.Wearing
goggles lightly tap the weak point with a centre-punch and light
hammer to crack the glass just at this evacuation point.I've never
known the whole CRT tube to implode doing this but the extra
protective cover should be used.
Note of caution for long-term storage of ICs
Some black conductive foam is hygroscopic in the long term and can
cause complete corrosion of the legs of ICs and trannies etc in an
ordinary storage situation ,not necessarily a damp garden shed.
To make coiled extending cable,where off the shelf multicore coiled flex is not
available
This method will work on relatively thick sleeved cable i.e mains rather than
signal.Find some wooden dowel of the intended internal diameter of the coiled
cable.Nail one end of the plain cable to the dowel,fix the other end of the cable in a
vice;twist the dowel until the cable "upsets".Roll the cable onto the dowel in
the sense that contracts the helix on the dowel,nail the end that was in the
vice.Now while turning the dowel heat with a hot air gun to the point where
the sleeving is about to melt,allow to cool.Someone told me using a pan of
boiling water as the heat source does the same job but I,ve not
tried it but it would give even heating.
To make a detent for a standard pot.
Assuming a standard D section of pot shaft. Obtain
some phospher-bronze door draught-proofing spring strip.
Cut off a small length and form the cut end into a rolled form
and mount the other end to allow the rolled part to press
against the flat of the D. For circular shafts, file a flat spot.
Dealing with fractured Monkey metal / Junk metal castings.
This is the metal that when fractured reveals a distinctive granular
appearance otherwise an aluminium type of colour.Glue back with
industrial epoxy then after curing drill angled holes through the plane
of the fracture and insert glued reinforcing pins (squashed along the length
with double action cutters or pliers to indent to give mechaniclal bond).
For thin metal make shallow angled pilot holes.Make a small clampable block
with an oversize pilot hole to guide the drill bit at a shallow angle or make
a chain drilling of about four holes,3mm deep to make a trough to allow location of drill bit
when drilling at an acute angle to the face.
Removing the nuts from bolts with recessed heads, eg coachbolts,
where the square part of the stem has been graunche dor the "square"
in the chassis graunched so the slotless head spins.
Assuming enough overhang of bolt.
Find a matching nut and hacksaw a slot in one flat.
Mount on the bolt anmd grip with mole-grips
so not to distort the thread. Then enough slack to grip
the internal part of the thread or perhaps grip
the head of the bolt then. Hacksaw a slot
in the head if re-using.
Conductive Rubber
Don't be tempted to use bicycle/motor cycle inner tube as rubber insulation. It
is slightly conductive,won't show on a 20M ohm DVM but put a 500V
Megger (insulation tester) and it will be perhaps only 100K.
De-soldering ICs
Use a hot-air paint-stripper,1400W,500 degree centigrade,with 2 level heat
control to prolong element life. Activity may appear fearsome but it is no
worse than a flow-solder bath.Pre-heat for one minute then apply to pcb,make
extractor tool to pull ic from component side. Make an IC extractor from an old large pair,10 inch, of
circlip pliers,the jaws need to open out enough to clip around the ends of up to 64 pin
ICs with enough force to overcome the mechanical force of the situation where all
the pins are angled relative to the PCB holes.Forge around both of the original circlip
pins,one joggle at right angle to clear the heigth of the ICs and a slight inwards joggle
to make purchase on the underside of the IC,grinding a wedge angle to the points
helps particularly where there is no clearance between IC and pcb.
[ Because of these joggles this tool is also useful for depressing the rear grippers
and releasing of that type chassis mount fuseholders and switches when internally surrounded by other
components ] .
I have to emphasise that you cannot use a "standard" IC
extractor tweezer, they are just not man enough, you do have
to manually pull with a few pounds of force to guarantee
minimum amount of heating of the IC.
For awkward positions lock the pliers to the IC by wrapping
a cable tie around the handles, tighten, slide down and
add a couple of notches to the tie and force back along the handles.
Use this technique for salvaging (working order) up to 64 pin ics ( when practised ),other
components, sm and even repair (tracks are not dislodged).For repair work beware of
spatter of molten solder causing solder bridges on adjascent compoents because if you
are doing the job properly,ie not dislodging pcb tracks the IC must be pulled out with
some force and the board tends to flex so possibility of flicking solder.
Mask off surrounding areas with wide aluminium tape or thick plummer's PTFE tape around
both sides of board to avoid unsoldering
and flicking off nearby minor components and trap any that do.
The secret is to be as quick as possible,idealy the body of the extracted ic will
be just about handleable rather than too hot to touch.Try practising on a board
with close packed TTL chips or similar and aim for an extraction rate of
something like one every 2 seconds.Between boards keep the hot air gun running on
low power setting (not switching off).Don't rest the gun against the board when heating
as vibration seems to affect the element life also don't allow the board to
flex back onto the gun for the same reason.Hold the gun so airflow is angled to the board
as solder spat directly into the nozzle can kill the element.
About the only components that cannot be removed with this technique are parts
moulded in soft plastic,e.g. crystal sockets,rf coils with plastic former (IF coils usually OK)
some DIP switches. Even these are desolderable intact if the body of the component is previously
cooled with a blast of aerosol freezer spray.
You definitely need a tool to pull the IC off the board as soon as the
solder is non-solid/breaking up ie before even fully melted quite possibly.
An old pair of long nose pliers with the ends ground down so the remnant
tips can be bent inwards to grab the ends of the IC would probably be
sufficient to show the method works.
Also definitely practise on an old/scrap board first as it needs that
confidence because otherwise pointing a glowing hot element and 300 degree C
or more blast of hot air at a pcb is not a natural thing to do.
SAFETY NOTE:- ensure good ventilation, use safety goggles because trapped
water etc in the capaillary structure of glass fibre reinforced PCB can super-
heat to steam and jet out molten solder,also it is possible to overlook small
electrolytic capacitors on the solder side of the board which of coarse explode
with the direct heat of the hot air gun and beware of very
slight risk of combustion of adjascent flammable parts especially where
components have extra (un-noticed) mechanical bonding leading to extended
duration of heating activity.
Dealing with certain type of inter-board ribbon connectors.
This tip relates to the connectors,usually white ,used by Pioneer and other
manufacturers. On first coming across these connectors they seem to be make-once
at manufacturing stage and cannot be undone. Pulling on the ribbon only makes
the angled teeth inside the body of the connector dig into the stripped conductors more.
The cover clip cannot be removed
because the un-stripped ribbon bears directly against the cover piece.One side
of this cover is thickened the width of the ribbon,find a piece of flat metal bar
the length of the connector body
and push down on the thickened part of the cover in direction towards the
pcb to release,localised finger pressure is not enough.
To free seized equipment knobs
For the situation where the knobs are seized onto the shaft by rusted
grub screws,especially where the screw penetrates the shaft;
after you have butchered the grub screw slot try this.
And it is one of ten virtually irreplaceable knobs.
Make up some guide tubes,small enough to just slide into the hole
in the knob containing the grub screw,these tubes drilled on a lathe with
a clearance bore to take a drill bit. This drill bit usually needs to be
extended by brazing onto a longish rod (so the chuck of the
drill misses the face of the equipment).
Use some cutting oil and drill into the grub screw.
Ideally use left hand drill bits and left-handed power drill
rotation, such drill bits are available from specialist suppliers ,
other suppliers may kook at you as though you're trying to wind them up
(anti-clockwise).
To convert a right hand drill bit well enough for this use grind the
cutting face back on the opposite rake angle, swarf clearance
is not relevant here. Often the bite into the drill bit
into the screw or the localised vibration or heating is enough to
shift the screw.
Now use a small "easi out"(maybe this is a UK trade name),but consist
of a coarse left-handed cutting thread on a coarse taper.
Wind into the hole in the grub screw and hopefully extract.
I don't use easi-outs as the smallest ones for this
purpose are very week and if it breaks you have
a lump of high carbon steel just where you don't want it.
Maybe appropriate for very large knobs only.
If this fails repeat the first procedure with larger diameter drill bits
and appropriate protection sleeves
until nothing remains of the grub screw,retap a larger hole and use
a larger grub screw for knob reuse.
To replace telescopic antennas
Where the pivot screw (usually brass therefore head easily
stripped) refuses to undo with normal torque.Use a set of
mole-grips (vice-jaw locking-pliers) clamped across the
pivot point starting with light compression and gradually
increase force until the screw undoes without undue
force.
For making reasonable looking copies of old bakelite or
unconventional equipment knobs.
Requirements:-
Flexible moulding liquid(obtainable from craft shops for casting chess pieces
etc),polyester resin and hardener,mould release agent if required,colourant,
broken rare earth magnet,iron filings,modern-day knob smaller
than required knob,engraving tool for vibration.
Procedure:-
Clean and polish knob from which a one-part mould can be taken{no severe
undercuts).Fix any old potentiometer to a metal plate locateable to a small
container (for precise alignment of knob),mount with shaft downwards.Remove
grub screw from the origional knob,place a small plug of cable sleeving in the
hole and reinsert the grub screw.Fix this knob to the shaft (fast but
removeable by pulling).Assemble mould jig and pour in moulding rubber,vibrate
with engraver to rid of air bubbles,allow to cure.
Mix resin and colourant,preferably keep cool to reduce viscosity.
Prepare the modern knob;mark radial position of grub screw on the rear surface
of the knob,repeat grub screw plug as above,fix to pot shaft..Extend the grub
screw hole with a piece of cable sleeving,plugged at outermost end with glued
magnetic material (length just clearing the side of the mould).
Mix hardener with the resin/colourant and pour in mould,vibrate with engraver as above.
Allow to cure.Demount mould,then with iron filings locate axactly the extended
grub screw hole and drill down to the grub screw,grind rear face of knob if
required,remove plug from centre of knob.
A refinement is to add punched discs,shapes or press-formed domes of brass
shim lightly gummed to the mould base to provide pointers or contrasting finish.
The colourant can be ground down broken bakelite knobs , if you can be
sure there is no asbestos fibre reinforcement to the knob/s.
Missing knob
If one of 5 matching knobs is missing.
Move them so the missing one is in the centre and add one of right colour
and shape but larger say, to the centre. Or if 2 say volume and dial scale
knob , one is missing , replace both with 2 from somewhere else.
To check out of circuit LCD displays for pinning etc,simply
Touch one pole of a 9V battery and the backplane terminal, usually
one of the extreme conductors. With finger of one hand touch other battery
terminal then with finger of the other hand touch
the other conductors (one or more) which should activate segments
Wet operatives might want to be more cautious.
I know this is dc but it doesn`t do any harm for short duration.
This tip applies to low voltage,low power carbon potentiometers where for
physical constraints it is not possible to replace.
Dismantle the pot down to the carbon track clean/degrease.
Make up resistive compound from photocopier toner and graphite powder
obtainable from locksmiths for dry "lubrication".
the following resistivity values are very approximate for .02 inch thick film.
graphite:toner ratios
1:1 ,200 ohm per square inch
1:10, 100k ohm per square inch
1:30 10M ohm per square inch
Mask off area surrounding carbon track,sprinkle on the powder,fuse the film
in a low oven approx 150 degrees centigrade or hold the barrel of a soldering
iron 1mm from the powder to heat .When fused lightly abraid with a
nail file,and reassemble pot.High ohmic pots are a bit iffy,low ohmic are fine.
p.s. I would be interested to hear of any suggestions for higher resistivity
addmixture for higher ohmic pots (for more even distribution)
Where the track is not too bad , just worn in arcs.
Open out or in the wiper blade/blades to use a different
part of track. If the wiper support can be wedged
away from the track then bend the wiper to give more
contact force. If the rivets have slackened on the
paxolin then squash with an old pair of basic red/blue/yellow single
action crimp pliers. To get to the wiper rivet
grind down the the interfering bulges a bit between the
red and blue sections. Add grahited grease on track
before re-assembly.
Hint for increasing storage space.
For doubling the storage capacity of an existing
wall of steel cased,plastic drawered component
storage cabinets.
Obtain some extruded aluminium channel sliding
door gear used in domestic clothes cupboards etc.
Fix the runners to the top of the cabinet/
cabinets.Fix channel to ceiling joists/stout shelf in
front of and above(to avoid fouling top layer
of drawers) the existing wall mounted cabinets.
Fix a couple of PTFE slabs to base/rear to run
against a sheet of wood or metal fixed under
the existing units.Cabinets can be doubled
up,pop-rivetted together vertically with bridging
plates across the joins.Even trebled up if heavy
components are placed in the wall units.For every
3 existing units maximum of 2 sliding ones for
access,for 4 fixed then 3 sliding etc.
Theoretically 2 layers of sliding and 1 layer
fixed cabinets would be possible.
Cheap UV Eprom eraser
Find a small personal sun-tan lamp easily found at car-boot sales,garage sales
in the uk for a couple of pounds. Replace the silica rod/element IR section
with an external mains lamp holder and lamp in the 50W to 100W rating to act
as UV lamp ballast.Plenty of room for eproms and erasure takes about 20 minutes
Ensure there is no UV light leakage to avoid
damage to eyesight
Hint for checking IR remote controls
To test Infra-Red remote controls for tv,vcr etc.
In subdued ambient light "shine" the zapper
at video camera,CCTV or cam-corder,if working then
should be seen flashing on monitor.
Not all lens/camera systems may be responsive to
IR so try with a known good remote control first.
Of course this check only shows there is a flashing
output from the LEDs,not necessarily the correct code
pulse train.
Hint for de-soldering surface mount ICs.
Use a hot-air paint-stripper,1400W,500 degree centigrade,with 2 level heat
control to prolong element life.
Form a ring of silicone covered wire around the IC{to isolate the remaing
components on the pcb.Push a thin piece of wire
under one side of the IC and form a loop around the IC,repeat on the other
side;this is to remove the IC when the solder melts, tug on these wires
while
heating up to ensure minimum heating contact time.
Place a slab of PTFE with right size hole cut into and
clip pcb and slab together with clothes pegs/Bulldog clips etc.
If the IC is for re-use then cover body of IC with heat insulating material
or blast IC with freezer spray.Allow the hot-air gun to get up to heat{say 1
minute}
before applying to IC.
For more crowded boards make "conical" shrouds to surround the IC. I used
some PTFE strip that i had but thin paxolin or similar but drilled and wired
together would probably do. Cut 4 small trapezoids from the PTFE
or tin-plate and wire at the corners to form a
truncated pyramidal frustrum.
Fixed PTFE together with paper staples but for the smallest shroud
for 8 pin SM had to wire together the final join.
Tie to the PTFE/ tin-plate cone (to stop the blower blowing it off) with
copper wire or temporarily solder to distant points.
When practised the heated contact time should be less than
2 seconds - no board distortion or collateral damage surprisingly.
If you can't get the tugging wires under the IC then pass
under a few pins at each corner.
Because this tugging frees the IC at the earliest moment, the solder
on the board is not fully melted and leaves a profile for localising
the new IC in place and then solder pin by pin.
Even for thick board and plated-through holes
so only tips of IC leads protrude,
very thin signal traces, traces to tiny pads on both sides of boards of same
pin in some cases and plated vias under ICs as well. I know if i used
"proper " vacuum assist desolder or butcher-and-remove-single-pins , many of
those traces/pads would have dislodged.
I had to sharpen the points of my large adapted circlip pliers to get the
extra purchase on the ends of 14,16, and 28 pin ICs. Not one dislodged
track using a paint-strip hot-air gun. Next time i'll have to take some
before and after pics for the doubting thomases.
SAFETY NOTE:- ensure good ventilation, use safety goggles,and beware of very
slight risk of combustion.
Device type EIAJ codings of form 2SC etc eg 2SB705 2SD2577 etc
First number is number of pins minus 1
S means semiconductor
Third term
A high frequency pnp
B low f pnp
C high f npn
D low f npn
E Esaki diode
F Thyristor
G Gunn diode
H single junction transistor
J p channel fet
K n ch fet
M bidirectional thyristor
Q led
R rectifier
S small signal diode
T avalanche diode
V varicap,PIN or snap-off diode
Z zener
Pro electron device coding
Of type B?? ??? (if silicon) eg BC 107
First letter A Ge,B Si,C GaAs and others
Second letter
A detector Diode
B varicap diode
C Tr audio not power
D power Tr
E Tunnel diode
F Tr rf not power
G miscellaneous
L power rf Tr
N optocoupler
Q radiation emitter as led
R control devices as thyristor
S switching Tr not power
T power control devices as thyristor
U power switching Tr
X multiplier diode ,varactor or step recovery diode
Y rectifier,boost or efficiency diode
Z voltage ref. or transient suppresor diode
Transistors marked A114, A124, A143, A144 etc if they are not
Germanium era , apparently fail diode dest and are ohmic
then are probably "digital" transistors, PNP, with built in bias resistors
of DTA114 etc. Similarly C114,C124,C143,C144 etc are
the NPN versions DTC114 etc.
Transistors marked N.... may be 2N....
Small components marked with an N.... with a dot underneath the N can mean
abbreviated form of UN.... series of Panasonic / Matsushita .
"X13" packaged transistors (plan view are boat shaped about 2x2x4.5mm )
with 4 numbers marked on top or side WXYZ probably means 2NWXYZ.
I was checking for data on an FT5154 transistor of 1976 kit
probably Fairchild manufacture, large F logo.
An old German ECA transistor data manual showed it equivalent to 2N5154.
A straight block of 50 or so others listed in that manual from FT1724 to
FT5154 showed the same FT series/ 2N series equivalence,
but not necessarily all.
FT??? in hundreds don't seem to have direct number 2N equivalent
And now a puff for Sci.Electronics.Repair FAQ Home Page by Sam Goldwasser
An excellent resource for repair of electronic equipment.
A site with links to info on early Tape Recorders and Video Tape Recorders
VTR links
A transformer winding company that does reasonable priced semi-custom transformers including valve jobbys ,Hampshire
Another transformer co. that does one offs,Devon
A loudspeaker reconing/recoiling company recommended by a customer
Valve and Tube Company IOW
Making your own thermionic valves (if skilled enough)
http://www.thelightbulb.co.uk/index.php
Some pages of links to electronics and repair sites
links 1
links 2
links 3
links 4, including for user manuals
surface mount device markings
Some surface mount fuse ratings as marking letter code (Schurter)
0.375 Amp E
0.5 Amp F
0.75 Amp G
1 Amp H
1.25 Amp J
1.5 Amp K
2 Amp N
2.5 Amp O
3 Amp P
4 Amp S
Television and Video recorder viewer adjustments, Contents , tuning in tuners etc
was on http://www.oh-bugger.net.nz/eric/tune_in.html
user manuals for turntables:
http://www.vinylengine.com/library.shtml
philips user manuals:
http://www.p4c.philips.com/cgi-bin/dcbint/cpproduct_selector.pl?slg=ENG
panasonic manuals here:
http://www.support.panasonic.co.nz/framemanuals.htm
general user manual collections
http://www.theusermanualsite.com
http://www.User-Manual-Search.com
Also mention of the deja news site now part of google.com
Deja News - The Source for Internet Newsgroups!
Select all rather than recent and put in keywords sci.electronics* and
one or two keywords of your specific interest.
A useful internet test-card for checking computer monitors (connected to internet enabled PC)
Something for the hifi nuts
was on www.netcentral.co.uk/satcure/audio/scam.htm
Diverse Devices,Southampton,England
Telephone number - the same number as it has been since 1988 but email is now the preferred method of contact so number deliberately not placed here.
I devote time each day to replying to emails.
(obscure/obsolete components,second hand test equipment, schematics etc)
Postal: 66 Ivy Rd, St Denys, Southampton, SO17 2JN Englanddiverse9@onetel.co.....m ( for anti-spamming reasons please remove all 5 dots ..... between co and m ) Plain text only (see below)
If this email address fails then replace onetel.com with divdev.fsnet.co.uk part of the address and remove the 9 . Please make emails plain text only , no more than 5KByte or 500 words. Anyone sending larger texts or attachments such as digital signatures, pictures etc will have them automatically deleted on the server. I will be totally unaware of this - sorry, again blame the spammers. If you suspect problems emailing me then please try using my fsnet.co.uk account.
More hints & tips and repair briefs on homepage http://home.graffiti.net/diverse:graffiti.net/