My Sidekick Reverb started giving me issues out of the blue. Lots of humming with nothing plugged in. Here's a video of the issue.  I found a wiring schematic and I opened it up to see if there was any obvious signs of damage but it all looks OK to my beginner's eyes.

Can anyone help me diagnose this issue?  If anyone can point me in the direction of some good troubleshooting resources, I have yet to find anything on my own.

Remove the speaker from the amp. If there is DC voltage leaking into your speaker it may damage it. Next use a multimeter set to read dc voltage across the speaker leads. What does it read? We don't want to accidentally short them together and definitely remove the speaker. If it is not DC voltage on the output it may be something right in the preamp. But first test the power amp side to be careful.

That sounds like poor power supply filtering to me. I'd check caps C30, C31, C26, & C27. First, make sure they are properly soldered to the circuit board. It's quite possible you just have a cracked solder joint on one of the caps.

Quote from: DrGonz78 on July 23, 2024, 08:13:57 PMRemove the speaker from the amp. If there is DC voltage leaking into your speaker it may damage it. Next use a multimeter set to read dc voltage across the speaker leads. What does it read?

Multimeter reads 0.15V across the speaker while it's buzzing..

Quote from: jasper2021 on July 24, 2024, 05:17:23 PM

Quote from: DrGonz78 on July 23, 2024, 08:13:57 PMRemove the speaker from the amp. If there is DC voltage leaking into your speaker it may damage it. Next use a multimeter set to read dc voltage across the speaker leads. What does it read?

Multimeter reads 0.15V across the speaker while it's buzzing..

Good.
To my ears it's too buzzy raspy rather than deep hummy, I suspect you lost some ground between amp input and preamp

What happens if you set Master to 0?

What if you short power amp input terminals together?

Trying to find *where* buzz gets in.

Quote from: The Dude on July 23, 2024, 10:29:36 PMThat sounds like poor power supply filtering to me. I'd check caps C30, C31, C26, & C27. First, make sure they are properly soldered to the circuit board. It's quite possible you just have a cracked solder joint on one of the caps.

Ok, so it looks like some corrosion (?) on the solder, and some of the connections aren't pretty. I think there might also be problem spots on the bass pot and what I think are fuses(?) Have a look at these pictures and tell me what you think: https://flic.kr/s/aHBqjBBdor

Good.
To my ears it's too buzzy raspy rather than deep hummy, I suspect you lost some ground between amp input and preamp

What happens if you set Master to 0?

What if you short power amp input terminals together?

Trying to find *where* buzz gets in.
[/quote]

I turned on the board with the speaker disconnected, and I could hear a similar buzz (quieter, obviously) that seemed tk be coming from the transformer... does that help?

Turning the pots didn't affect the speaker buzz at all...

By short the power amp input terminals you mean connect them? And see if it buzzes or am I checking voltage at the speaker leads again? Forgive my inexperience - I know basic circuitry and can do house wiring and car stereos, but that's about as much troubleshooting as I've done.

That's not corrosion. It's flux. Not a problem. If you turn the master all the way down (as Juan suggested) is the noise still present? Also, grab the top of those caps and give them a SLIGHT wiggle. That might tell you if any are loose.

Quote from: The Dude on July 24, 2024, 06:57:15 PMThat's not corrosion. It's flux. Not a problem. If you turn the master all the way down (as Juan suggested) is the noise still present? Also, grab the top of those caps and give them a SLIGHT wiggle. That might tell you if any are loose.

One of the connections is pushed through on C31, and it looks like it's taken a piece of the PCB off with it. There's a flake of it attached to the solder.

If I turn the master up, there's some pops and squeals that get louder. This I did after jiggling the cap; I haven't heard that yet. Turning the master down stops that, but the buzz continues unaffected.

You'll need to resolder that cap leg and maybe jumper the trace to make the connection.  Hard to say for sure without seeing a pic.

https://flic.kr/p/2q78Dor

That trace looks broken. You will need to scrape off some of the coating and solder across the break. If not completely broken, I'd do it anyway to add stability to the cap leg.

Oh yeah The Dude said it. Scrape off the green stuff and bridge the crack. I sometimes use a piece of stiff wire to make the connection with solder. If it is a big trace I have even used scraps of solder wick and that works amazingly well.

I ended up soldering a 22ga wire, jumping from the bad connection to the next solder joint in the circuit. Works like a charm. Sprayed some deoxit in the pots and now it sounds better than ever. Thanks everybody!