Help Me Bring a Trash 5150iii Back to Life

[CanserDYI]

If you don't have the footswitch connected, do you still have the same issues with channel flicking? If there's an issue with a lead on the board or any solder joints they might be breaking the moment a bit of heat is introduced to the amp.

Same issue no matter if the foot switch is plugged in or not.

 

[Edika]

Same issue no matter if the foot switch is plugged in or not.

It seems then the issue is at the switching circuit. I'm not sure if this is on the main circuit board but if you find the schematics and locate it, you can test the components to see if they're problematic. If not maybe resolder them to be sure they're performing correctly. That is, if you're comfortable with all of that. Otherwise, a trip to a tech it is to avoid electrocution and salvage the amp.
But if the channel switching is in an isolated board, them maybe you can find a replacement and put it on.

 

[EdgeCrusher]

It may be worth noting that the cable for the footswitch should be a speaker cable, not an instrument cable. Looking at your photo it seems you may be using an instrument cable. This may not solve the issue, but could potentially be the cause?

 

[CTID]

It's possible you already have, but always good to plug into the effects return and just bypass the preamp entirely, see if you can isolate where it's starting. Not sure if that'll make a difference if it seems the whole amp is shutting off, though...

 

[TedEH]

It may be worth noting that the cable for the footswitch should be a speaker cable, not an instrument cable.

Why? I don't expect a high amount of power going through that cable, so thickness doesn't matter, and it's not carrying the actual guitar signal, so shielding doesn't matter.

It's possible you already have, but always good to plug into the effects return and just bypass the preamp entirely, see if you can isolate where it's starting.

It could be useful to try the opposite as well - grab the preamp out from the send and see if you can power it with something else.

 

[CanserDYI]

Yep, my thoughts already guys. Already tried preamp out and return in as well as bridging them, deoxit'd them and cleaned em, and tried again and nada. It's at the tech as we speak, should hopefully be done tonight he's actually really caught up for once. Stoked, got a 50 watt stealth for free ninety nine.

 

[Crungy]

Yep, my thoughts already guys. Already tried preamp out and return in as well as bridging them, deoxit'd them and cleaned em, and tried again and nada. It's at the tech as we speak, should hopefully be done tonight he's actually really caught up for once. Stoked, got a 50 watt stealth for free ninety nine.

Nice! Did he say anything yet as to what may have been the problem?