Trouble With New (Old) Peavey Bandit

[tube power]

I bought a used Peavey Bandit the other day.
(A previous bandit many of you walked me through repairing is sounding awesome btw.)

This is a teal stripe and I love it.
But after being in my frozen garage the other day, when I turn it on,
sometimes it sounds like a little transistor radio, very faint.
Happens on either channel, reguardless of settings.
Magically, when a slight "Arthur Fonzarelli" shot to the top is applied with an open palm,
it springs back to life. (probably wrong, but I had to try doing that)

I tightened all the jack/control nuts on the exterior, still sketchy.

Seems like one time I flipped the ground switch up and down and it popped on.
So I'm thinking it's a ground. Could be a bunch of solders I suppose.

Any advice on where to start looking when I pop it open would be much appreciated.

[Enzo]

No, not ground. Flipping the ground switch sends a little bump through the chassis just like whacking the top.

When it gets this way, take a spare plug or cord and poke in and out of the FX return jack and/or Power AMp In jack. Or even INSERT jack. The amp ought to have one or more of those. Does that wake it up?

[tube power]

Absolutely, FX does it almost every time.
What's going on?

[Enzo]

When you are NOT using the FX loop, there are little extra contacts inside the return jack that carry the signal past them. If those contacts get dirty or oxidized, then the signal can;t pass. You need to clean those contacts or at worst, replace the jack.

And to get through the gig, take a spare cord and connect FX send to FX return. A sort of external bypass. That will not harm the amp in any way. See if that cord cures it.

Sometimes you can squirt contact cleaner into the jack and probe it a few times, otherwise you have to go inside.

[tube power]

Thanks, I'm going to clean all of them since this amp is like 20 years old.

I do use the loop for flange and delay, sounds great that way.

[Enzo]

If you have to take it all apart anyway, then check very closely the solder on all the jacks and the controls too.