Ampeg ss140c no sound

[boog]

the zeners after the regulators tested good, so far I've lifted jw13, jw14, jw15, jw7(I think? going to pin 8 of ic5) r30, jw9 below jumper j3 trying to narrow down where the problem is.
sorry didn't think to post a schematic

[glebert]

I flipped one of these a while ago that was acting very similarly, and IIRC there are two big power resistors mounted up near the chorus controls that can cause the preamp to be nonoperational, and because of their size and the way they are mounted they are prone to solder cracks.

[boog]

that would be the ones, someone attempted to repair it before it was brought to me, that part of the board was a mess, caps soldered to the wrong side of the board, blown regulator, 2 blown op amps, and they replaced one of those big resistors with the wrong one, it's hard telling what else I'm going to find once I can keep the power on for more than a minute at a time

[DrGonz78]

R61 & R62 will get very hot since they are dropping resistors. Next time you turn on the amp measure the voltage drop across those two resistors. Use ohms law to calculate total wattage dissipation if you want to make sure it's safe. It probably is fine and they are 10 watt resistors. Instead of worrying that they are dissipating too much find out and then you will feel better.

[boog]

I understand they will get hot, but i thought it was a bit excessive, they are dropping from 44v to around 20v then regulated to 15v, but somehow I missed that one was a 100ohm when it's supposed to be a 180ohm, the joys of someone elses failed repair

[DrGonz78]

Yup the joys of amp repair when somebody else took a stab at it already. Sounds like your making good progress on it though.

[boog]

I'm making progress, I'm still waiting on the resistors from mouser, the went ups when I picked fedex, so it's taking longer than usual.

[boog]

more progress made, finally got around to putting those drop resistors in, power seems to be correct now, still no sound so I pulled the preamp board and found more surprises, burnt traces, one of which had been bypassed with wire, and one that hadn't, both were -v feeds to opamps, after finding 3 bad opamps I went ahead and replaced all of them on the preamp board, good news is I have sound now, but only on the right/chorus channel, left/dry is not working, there is signal, I can slightly hear the overdrive channel if the volume is almost full on, and I get a big hum if I try running something into the left power amp in jack, next will be poking around the power amp board, then fixing the first depth control on the chorus that isn't working.

[boog]

Got this one finished up, the chorus control wasn't an issue, it was me overlooking it having one for each channel, oops.
As for the left channel: after pulling everything back out of the amp I found that someone had left 2 joints on the left power amp in jack completely desildered, fixed that, checked a few other parts anyway, but figured the rest of the path was ok since I did get a loud hum when I tried using that jack before.
I put it all back together and everything works and sounds great, with the exception of the terrible chorus lol.