Not yet, I had shelved it pending finishing some other projects. I’ll try to get it back on the bench this week and have another go.
I replaced the 4 bad caps (C66 thru C69). I determined R113 and R114 should be 220ohms based on their color band. However, I did not replace them since they measure ok at 215 ohms. I learned how to test a zener diode, and confirmed that D31 and D32 are zeners 15volt, 3watt. I removed them from circuit to test them, and after confirming they are good, I returned them to circuit. Now the amp seems to be working fine. Before repairs, the amp had a lot of annoying hum.
BTW, the pcb beneath these components (C66,67,68,69, R113,114, and D31,32) has been overheated and is discolored. However no traces are damaged, and the 4 caps were the only failed items. Without a schematic, I can't really say what function this grouping of components is serving. But I have seen online pictures of someone else's same pcb with the same burn spot in this same exact area as mine.
I will be monitoring for continued overheating, but am hopeful it was a result of the caps failing.
Cheers
You could have put the caps and Zeners slightly off the board, and used higher voltage rated caps, as this appears to be a manufacturing / design fault.
You mention seeing pictures on the net with other units having the same problem, which means this is a common, and known issue.
You mention seeing pictures on the net with other units having the same problem, which means this is a common, and known issue.
I just got one of these on eBay which the seller claimed was working fine. It was packed poorly and the speaker terminals were knocked in on one side, but still seem electrically connected. I plugged the amp in but was unable to get it to do anything, no lights or clicks or anything. Does that match the symptoms you were both seeing?
I'm trying to determine if I should bother replacing them. It sounds like your amp was more functional than mine before you replaced them. I tested all the fuses for continuity and the switch appears to work, I don't know what else to test beyond that.
Any luck?
Mine also looks like it has some discoloration around D31,D32 but also has leaking capacitors:
I'm trying to determine if I should bother replacing them. It sounds like your amp was more functional than mine before you replaced them. I tested all the fuses for continuity and the switch appears to work, I don't know what else to test beyond that.
Maybe if you have a AC voltage and DC voltage ...
@huggygood thanks for the push to get back to basics. I found that the power cable I grabbed (which worked fine a month ago) had a break in continuity for the live conductors. My amp works fine, now I just need to repair the speaker terminals and replace those leaky caps.