My JC-160 is acting weird

[UglyCasanova]

So, this is my old paint-stripper



Someone in our rehersal space borrowed it and didn't turn it off. I don't know how long it's had been on, but I'm guessing anywhere from 1-4 days. Now, whenever I turn it on, it works for like 5 minutes before it just cuts all sound. The pilot light still lights up. I've already got a replacement amp many, many months ago, but as we're moving to another space in a few months I figured I'd either try fixing it or throw it out (which would be a shame). My real question is, I guess, what am I looking for and is it likely that I'll be able to get my hands on the required parts and will I be able to replace any fried parts myself, or will I simply end up electrocuting myself in the process?

I've only removed the back board to see if I could take a peep inside, but apparently it will require some more work, which I didn't have time for after today's band practice. I hope to return in a few days to take a look at the circuit.

I got it dirt, dirt cheap, so sending it in for a repair somewhere is probably something I won't end up doing.

[moid]

I am no expert here (and please make sure you completely unplug this from the mains before opening it, the voltage inside an amp can easily kill you) but maybe if the transformer is burned out / worn out / got too hot having being left on all that time, then everytime it is now on, it gets warm for a few minutes, then gets too hot and can no longer pass enough electricity into the circuit to make the amp work - there's enough to keep the lights on, but not enough to make sound (or maybe very faint sound?). I have no idea how you fix this though, hopefully someone with technical skills can add some advice.

[UglyCasanova]

Yeah, I've plugged it out for sure,but I'm not sure how much electricity builds up in these SS amps, so I thought I'd ask before going anywhere near the board.

And there's no sound at all once it goes into this new automated standby feature.

[fuzzisokiguess]

Unplugging the amp is important but there is more to do to keep you alive (no haha). Yeah, line voltage can make your teeth rattle, but the electrolytic capacitors can hold hundreds of volts for days. Don't poke around in there unless you're equipped to discharge those (perfect spot for a twss, but too important- for reals).

Pilot light is likely getting voltage from a different part of the circuit or a separate tap on the transformer. So prolly not the power transformer. And too much current draw would blow the fuse(s), so likely not that either, though now that I think about it, it might have a protection circuit with a fuse that can reset. (Which would make sense, as you're able to repeat this same process). So, in that case: protection circuit working, but as to what would be causing that current draw? Dunno. I'll see if I can find a schematic around the interwebs.

I know I'm not being much help, my experience with SS stuff is little-to-none. Doesn't sound like an easy fix tho, and replacement parts could be tough and/or $$

[JonnyAngle]

Did you try jiggling the guitar cable?

That’s what happened to my peavey. Solder joint needed remelting.

[crochambeau]

Yeah, could be a bad solder joint plus thermal drift. Old filter caps might have a high enough ESR that they heat up and work a joint in the power supply?

I'd also scrutinize any high wattage (larger) resistors in the amplifier section, if something has drifted the actives in the amp section might be pulling more current than designed, which will also heat stuff up. If there's a thermal cut-off it might be a protect mode.

If you know anyone with a thermal imager it can tell you LOADS about what's happening without poking around.

Intermittent problems are a pain in the ass to troubleshoot. I'd give it a visual and see if anything looks wrong, then hope for the best.

[UglyCasanova]

Did you try jiggling the guitar cable?

I am a caveman as well, so yes.

Thanks guys. I'd rather not die trying to fix this thing, so chances are I'll put it up locally for free pickup for someone who actually knows what they're doing.

[comesect2.0]

Leaving an amp on for 4 days is an issue?
I leave my peavey on for weeks and have had it for 8 yrs.

[crochambeau]

Leaving an amp on for 4 days is an issue?

Shouldn't be, if everything is in a healthy state to begin with and your mains power isn't trying to carry lightening or other stupidity. I have some stuff in my to-do pile that shoots out of the safety zone in well under an hour.. even electronic parts wear out.

The power amp that runs my living room is left on for weeks at a time too.

[UglyCasanova]

The power there is not reliable at all, and this amp has seen some shit over decades and probably things you people wouldn't believe after I got it. Yes, Blade Runner reference.

My friend wanted to look at it. So at least I'm safe.

[Chankgeez]

Yes, Blade Runner reference.

SS amp bucket list:

• Attack ships on fire off the shoulder of Orion
  
  C-beams glitter in the dark near the Tannhäuser Gate
  
  Time to die.

[UglyCasanova]

Perfect.