peavey 5150 1st gen combo

[jack von]

hey everyone i was working on my 5150 2x12 combo and accidently shorted accross jp632 and jp633 now my preamp section is down i cant see any visible damage any idea where to start looking? and thanks in advance

[52 Bill]

hey everyone i was working on my 5150 2x12 combo and accidently shorted accross jp632 and jp633 now my preamp section is down i cant see any visible damage any idea where to start looking? and thanks in advance

I'd check the internal fuses to see if any have blown. Test with a meter, as sometimes they can look okay but still be open.

If the fuses are okay, then power supplies are the next thing to test.

[jack von]

fuses are good tested for continuity and there all banging

[Jazz P Bass]

What does jp632 & jp633 do?

No schematic attached.

[Enzo]

Schematic no help. The jumpers are identified, but the layout doesn;t show traces, so all we know is jumper X is near such and such part, but not that it connects to them. The schematic does not show jumpers. SO the OP needs to trace those two jumpers back to specific parts so we can identify the circuit... OR... just troubleshoot the amp and forget how it came to be broken.

[jack von]

runs straight from the jumpers i mentioned to R62 then through the center leg of Q8 r62 tests good noy sure how to test the little Q8 6531 simiconductor

[jack von]

http://music-electronics-forum.com/a...5150-combo.pdf

[Jazz P Bass]

It seems that you are in the Footswitch area of the circuit.
Still not sure where those jumpers go or what they are attached to. (that would help)

If the preamp is down you have to check, first of all, the +23 & the -23Vdc supply.
I have attached a cropped schematic that shows that supply.

[jack von]

the circut i shorted runs to v5 preamp tube im thinking this is the phase inverter ? and now one power tube is red plating as well i have signal from the preamp erction but it is very low

[Jazz P Bass]

It does not help 'thinking' it may be something or other.

Trace out the jumpers, where they go, on both boards.

[Enzo]

You know, we can expend a lot of mental energy trying to puzzle out what is wrong from what we think might have happened when we touched something with our probes. But I think the way to fix this is to simply find out what is wrong with it.

In classic troubleshooting, you explore the voltages and things as they should be. Two things that are next to each other on the circuit board may be far apart on the schematic, and have no relationship to one another.

If your trace went through R62 to get to the base of Q8, then the trace you are looking at is ground.

Q8 is a channel switching circuit relay driver. If it were bad, we'd be stuck in one channel, but the channel ought to still work.

Am I correct that a signal plugged into the FX return comes out the speakers OK?


Note the tube order for small tubes is V1-2-5-3-4, they are not numbered in order. V4 is the phase inverter.

If your preamp doesn;t work, then just diagnose what it needs. Are the heaters running on all the tubes? Two of them run in series across +24 and the other two in series across -24. Is there power in the circuit? Is there B+ on pins 1 and 6 of each tube?

Find little Q1, is it stuck on? In other words while the amp is running is R28 shorted across? Have the post controls up for this reading. Or worse, is there 15v across it?

[jack von]

fx return i have strong signal at speakers so power side is fine all heaters are on in all preamp tubes i have not checked voltage across 1 and 6 verry sorry guys as i am not an electronics engineer.

[jack von]

also i mis typed that circuit i shorted runs to v4 not v5

[Riffraff]

Make sure you check the harness used to connect those jumpers too. Those plugs seem to be prone to failure. I just ran into it on a 6505+ is was working on (same amp as 5150 II). When I did some research on it I found multiple people having the same issue with those jumpers in numerous circuits. They get loose which causes them to heat up which distorts the housing causing the contact to move away from the header. In some connections this results in a burn and sometimes even scorches the board at the connection point.





The fix for me was to pull the problem harness and hardwire the jumpers. I was lucky and the board wasn't burned so I just reflowed the pin in that spot then soldered wire jumpers pin to pin. Others that had board damage had to isolate the burn area buy cutting the trace with a razor knife and reconnect with wire jumpers further down the trace.