100C 250 watt amp with blown right channel. Both fuses on preamp blown. (stock speakers, no addon's)
Found a broken leg on a cap on the crossover for the high end, replaced.
Replaced right side transistors and fuses. Checked transistors and diodes on preamp board. (last revision with LED's on board)
Sound is crackly on right side. Moved right side wires to other side. sounds fine. Swapped with known good crossover still crackly.
Swapped with known good amp. works fine 100%. (okay, speakers and crossover, output transformers, are all fine.)
Swapped preamp boards left to right side. Crackle stays on the right side. Swapped the equalizer/input board from the known good amp. Still there. something on the output side...
Thinking bad transistors...swapped again with new set, new insulators...still there.
swapped out the "heatsink diode board" and it's still crackly. (note: I have found a few of these with broken solder joints. often this causes the fuses/transistors to blow as soon as it's powered up)
It defies all logic.
These transistors I have been using are some I ordered a few months ago. I ordered a dozen of each of the transistors from mouser. they are "STmicroelectronics" branded 2SC6284/2SC6287 's. They aren't some cheapy ebay counterfeit deal...at least i don't think, they should be legit but who knows these days.
I did use a transistor set from this pack to repair another amp (In fact, the known good amp I used in these tests) a few months back and haven't had an issue with that amp.
i'm going to try swapping the output transistor pairs left to right side tomorrow to test if left side becomes crackly. that will confirm if it's the transistors or not.
EDIT: bad cell phone spelling can't see to edit for nothing.