Another Antique Peavey

[mhuss]

I have an old Peavey PA head on the bench with the 200 watt module on the back, and it has an odd problem. The volume keeps intermittently cutting way down. I checked and cleaned the cable that connects the front board to the back module, but it didn't make much difference. I also did the usual chopsticking about, nothing seems loose, and the wave solder on those old Peaveys is usually pretty solid. The odd thing is that the signal on that connecting wire gets about 10x larger (on the PCB at both ends) when it gets quiet. This certainly smells like an intermittent semi-open (remove the load, signal gets bigger), but I see nothing obvious, and the signal changes the same 'backwards' way on the amp side PCB as well. The front end of the amp module looks like a discrete diff amp. Anyone seen this / have a quick fix in their bag of Peavey tricks?

[The Dude]

What model and have you checked any of the loop jacks?

[mhuss]

XR-400. The only normalled jack is Main Out/Graphic in, but that's a good suggestion, I'll check that. Thanks!

[J M Fahey]

Weird symptom, but if it's there, it's there.
That said, wire does not create signal by itself nor amplify, so I'd check the last active stage feeding it.
Please somebody post the schematic and show which is the weird acting wire, mainly to identify what's driving it, what signal does that stage receive and what connectors are involved..

[Jazz P Bass]

Here is what I have.

XR 400 200H MODULE A SERIES.zip

[mhuss]

Thanks for the schematics. I forgot that the normalled jack was on the preamp board, so even if that has a problem, it wouldn't explain the behavior I'm seeing (which seems to be happening 'South' of the front panel PCB).

[Enzo]

Considering the front panel jack ha the graphic and other circuits after it, isolate the problem. Pull the umbilical cord and run the power amp alone. Use clip wires to feed signal directly to the five-pin connector pins. Does the problem still occur?