Hate those fake updates from USPS where their computer sees that nothing has happened for a couple of days and inserts some generic "oh, we've totally put it on a truck and it's heading to you!” It has been sitting there for 3 days! Definitely not arriving today. 😔
Grouped what I think is +5V regulation on secondary side. With my extremely limited understanding, seems anode side of opto D8 is managed by HA17431 IC8. If +5V voltage falls then opto turns on and asks for more juice. Too high or just right opto is off. But how is over current handled? Could IC8 be bad and that's causing the power supply to go into over current mode?
Doing some searching about how a diode in reverse can be used as a voltage regulator leads me to Zener diodes. Looking at D22-D26, D26 has a black stripe while the rest all have green stripes. D26 must be a zener diode.
If I lift D26, will that prevent the +5V rail from coming up? Will something else on the power supply blow up without it?
Remembered I had a big variac. I was able to get the power supply to start by slowly bringing up the AC voltage. It’s hard to repeat, but I was able to do it more than once.
Sometimes those impulse purchases turn out to be pretty handy. Bought this endoscope several months ago and it has just been sitting around. Can see the labels without having to tear all the components off. #electronics#electronicsrepair#RetroComputing#VintageComputing
One for the JFET experts - I'm repairing a vectorscope which has a blown input FET on channel A.
This is the input circuit - A and B are the same, and the A and B input FETs (BF244Bs) are called out as "matched pair".
What parameter do I need to measure and match?
I figured Idss but that doesn't seem to have cut it, as the A- and B-ch have an offset error between them. #electronics#ElectronicsRepair#JFET
Update: the last time I tried to turn this thing on, it powered on but no display. Buttons worked, knobs worked, no lights. Something tells me somewhere I either bent a pin too far or broke it in the cable... I'm expecting I didn't break anything. I don't know too much about 80s/early-90s display tech, but I'm very certain that most things that would be connected to those cables, are not the kind of thing to fail silently when incorrectly connected. No pop and no smoke tells me I probably just missed a connection.
New cables on order. 100mm same-side 1.0mm 12-pin pitch FFC. Pennies. Then it'll be round 2. And, now I have the cabling to DigiRig this thing as well.
Does anyone have a good transistor cross-reference or search tool? I'm trying to replace parts like the Unisonic 8050S (a weird NPN part from the 80s) with something in the 2N, BC or 2S range.
Search by package, pinout and Vce/Ic limits would be ideal!
As handy as NTE's site is, it usually just says "buy this NTE numbered part", and I'd like to know what else might be similar. #ElectronicsRepair#electronics
Tonight's repair project - the power supply for an Acorn R260 (same as the A540 and A400 series power supply). Old style switcher with NPN chopper and a jumper wire to switch between 240 and 120 volt input.
Both the phase and neutral fuses have blown. The diode bridge is fine, as is the chopper. No evidence of burning... Very strange. I don't want to replace the fuses until I find cause of failure, but there doesn't seem to be one? #RetroComputing#electronics#electronicsrepair
I'm going to be fixing this Pioneer CLD-1750 in a few weeks (my next spare time slot). Fault is it doesn't read discs. Laser moves, focuses, moves in, focuses again, then gives up. No spindle movement. Anyone have any ideas? I'm hoping it's not laser failure - but it glows red on camera.
I've tried cleaning the laser lens. #electronics#laserdisc#electronicsrepair
Can somebody, familiar with these kind of #electronics, please help me to identify this transformer, which was part of the power supply circuitry inside a #projector.
A colleague of mine brought me his broken #beamer after, according to him, it had sparked out of its ventilation slits near the power plug, when he plugged it in.
I looked at the circuitry and it became rather obvious that the transformer gave out, as the PCB was charred around it.
Has anyone reverse-engineered one of the "600W" Chinese buck converters? Topology seems to be a fairly standard two-FET buck, but all the chip markings have been scrubbed. Curious if anyone's figured out what they are. This one died after only a day in service. #Electronics#ElectronicsRepair