I have swapped it with PC94.
I have replaced that capacitor right now and there is no change.
What kind of voltage should I have at pins 4 and 5, of the IC?
I'm getting around .200V. If I remember correctly, I used to get here 324V.
PC94 connects directly to IC92 and if IC92 blew up, there's a high chance PC94 was also damaged. So you may have swapped two bad optoisolators with each other. Check them with a test circuit, if they're bad, buy new ones. I wouldn't swap them with the others in case they are faulty and cause more damage elsewhere.
That's odd about the voltage going down. Do you still have ~324V on the primary capacitors? Or has it also gone down to 200V?
"Tantalum for the brave, Solid Aluminium for the wise, Wet Electrolytic for the adventurous"
-David VanHorn
I have tested three optos: PC92, PC94 and PC95.
Used a power supply and a resistor. As I increase the voltage, the resistance decreases.
The 325V is still there, at the main capacitors.
At C902, I have 326.3V.
Pictures are not the best, taken inside with phone.
In some spots looks messy, because I have tried removing, that white foam thing.
I am suspicious of this value. I would have thought it would be something higher than that. Maybe there is a bad part on that rail somewhere. Can you start lifting parts that go across that rail to ground and see where the resistance changes? I wonder if something is a bit leaky. Maybe a capacitor, or the shunt regulator.
Or D921 itself is leaky. It could be that on test with low current it's OK, but when it sees the full load of the power supply, it's effectively a short. If you have something you can swap it with, I'd try that too.
From the schematic, there's nothing to suggest to me that the resistance to ground from that rail should be that low.
Also I find this odd. Unless you are running at 230v line voltage, the voltage at C902 should be 160v DC or so. According to the schematic, it's powered from a full-wave rectifier (D901\D902) straight from the AC, so it doesn't have anything to do with the voltage doubler of DB91\C903\C901
This time, I could not find that low resistance at D921. I don't know, how did I measure that resistance that time.
I did something stupid, twice. I have discharged the capacitor C902, with two screwdrivers and blew two diodes D901 and D902. I need to buy more diodes, to be able to continue.
Yes, IC91 it was one of the original blown one. I have replaced it again later one, because it was shorted again.
I have removed those jumpers and there is no 5V. Some milivolt variation only.
If so, it could be that a bad snubber network keeps destroying the IC.
Remove D910, C911, check that the resistance of R979, R980, R981, R982 in parallel is exactly 470k divided by 4, ie: 117.5k - If it's off, one of those resistors is bad. Replace the lot.
Replace with brand new parts, D910 and C911 (note: 1kV part), and of course, IC91 again.
D914 could also be suspicious, and if bad would cause IC91 to be damaged. Even if it tests fine out of circuit, it might be intermittently failing. Likely worth it to replace it as well.
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