Amp cutting out

[rhaigh]

I'm having trouble tracking down the problem with a Laney combo amp that has a solid state power amp section but a 12ax7 in the preamp. The problem is that the amp cuts out sometimes. The power is still there but no sound. If you crank the volume real fast it will cut back in for awhile. If I take a wire (with nothing attached the the other end) and touch off of certain areas of the circuit, it cuts back in. I re-soldered all the soldered connections but it did not help. The problem seems to be post preamp as all three channels have the same issue.

Any idea on what could be up with this?

Thanks.

[Euthymia]

If there is an effect (or pre/power) loop, jumper the connection with a patch cord and see what happens.

If you are poking at various areas of the live circuit to see what makes it cut in and out (which is a valid troubleshooting technique when done correctly), it is best to do that with something that is stiff and not conductive, like a chopstick or the body of a Sharpie pen. Also stick your non-dominant hand in your back pocket.

[rhaigh]

I've tried jumpering the effects loop but it makes no difference.

I have to use something conductive to poke the circuit... that's the part I'm trying to figure out... Why when something conductive is touched on the signal line, does it start to work again? I'm not just taking a pencil to poke at areas to see if something is loose

Thanks.

[Enzo]

Because touching the signal path makes a brief loud signal. I would not be surprised if you can turn the guitar all the way up and BANG a super loud chord and have that wake the amp up. The momentary signal voltage spike is enough to spark over whatever loose connection is causing this.


Ball up your fist and whack the top of the amp hard, does that wake it up? Or for that matter, does the amp react to the whack in any way?

[Euthymia]

I'm not just taking a pencil to poke at areas to see if something is loose

Why not?

Not with a graphite pencil, which might be conductive, but with a wooden or plastic stick?

It's a troubleshooting and fault-testing technique I do every day, if not on every repair. Tells me if there's a loose component or connection on the board.

[rhaigh]

Thanks Euthymia. Yeah, I have troubleshooted that way, I just meant in this case, the wire touching the signal path make the amp wake up was stumping me. A chop stick is a good idea though I have used a sharpie Sorry to have sounded confusing. Thanks for your help.

Enzo, Even though jumpering the effects loop did not help, I plugged and unplugged a cord into the "send" jack a bunch of times and now the amp works. I cannot get it to cut out now. Perhaps a bad or dirty jack (it is soldered in well). Hopefully it stays like it. Thanks

[Euthymia]

I would chalk this resurrection up to the notion that there is probably one big PCB in that amp, and you managed to mechanically knock it back into functionality by wiggling the Send jack (which is probably directly attached to the PCB).

The switch in simple FX loops is usually in the Return jack. It usually doesn't take much to scrape enough oxide off the contacts to get it working again, for a while. You might shoot some DeOxit red or gold into that Return jack if you haven't already.