Quote:
Originally Posted by dr.ido
I've seen more of these with bad buffer and/or sustain boards than with bad power supplies. Check that buffer board isn't shorted before replacing the sustain board. A shorted buffer board can kill the Y-sustain board.
In your second picture there it looks like there is a heat mark on the Y-sustain board. There will probably be a FET on the other side of the board that has gotten too hot.
I've found and replaced shorted FETs on these before, but more often than not there are other faults. Easier to replace the Y-sustain board with one pulled from another set.
These panels crack very easily. I've cracked a couple myself while handling them (especially frustrating when it happens AFTER you've fixed it).
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I pulled the Y sustain board and where the darkened spot is there are 3 diodes, (surface mount) 2 appear to be standard diodes, and one Zener diode right behind the spot that looks dark. Problem is the diodes check good with the ohm meter using the diode check function as well. I'm going to hold off and replace the power supply, then if that doesn't work, I'll go for the Y sustain, along with a buffer board. I also checked other transistors, and diodes and couldn't find any bad ones. Although I could very well be missing something. I don't have an ESR meter, just a standard capacitor checker on my meter, and an old capacitor bridge with the green glowing tuning eye tube. In order for me to check them I would have to pull the caps first. Too risky to do that with these intricate circuit boards.