I just bought a 1976 PA-100, $20, in good shape, didn't work. Pulled the chassis, noticed a strange bend in it (on the PT side), appears to have been DROPPED.... After repairing two broken solder joints, it started working only when I accidentally grounded an edge of the pcb (I know bad practice 🙁 ). What I had grounded was a large foil bus, connected to all the gain pots (4 input, one master). Haven't found the exact schematic online yet, but other Peavey designs run all their pots to ground. So why wasn't this bus grounded intentionally (a screw to the chassis or something)? I figure because it must run through something before ground....like a small resistance (for hum)? Any ideas? Got a schematic to share? It sounds nice, especially the real spring reverb... Thanks!
If it's been dropped you may have a cracked PCB somewhere, sometimes they are impossible to spot, and you have to fault find their location.
As you already know the fault (no ground connection to the pots) you should be able to follow the PCB tracks back to where it's supposed to go to ground, even without a circuit.
As you already know the fault (no ground connection to the pots) you should be able to follow the PCB tracks back to where it's supposed to go to ground, even without a circuit.
A couple thoughts.
Don;t search the web for the schematic, just contact customer service at Peavey and ask for it.
Is this what you have?
http://assets.peavey.com/literature/manuals/pa100.pdf
do you have the board out of the chassis for these tests? perhaps the board is expecting the preamps stages to be grounded via the panel. The real old PV mixers with the big knobs even had to have the top chassis (the panel) and the lower chassis either screwed together, touching or clipped to complete grounding.
I don;t know about other models and grounding, ceratinly a lot of PV gain controls are feedback resistances on op amps and not grounded at all. On this amp, the master is a conventional voltage divider with the lower end of the pot grounded, but the channels use a feedback system, and the WIPER is grounded.
Don;t search the web for the schematic, just contact customer service at Peavey and ask for it.
Is this what you have?
http://assets.peavey.com/literature/manuals/pa100.pdf
do you have the board out of the chassis for these tests? perhaps the board is expecting the preamps stages to be grounded via the panel. The real old PV mixers with the big knobs even had to have the top chassis (the panel) and the lower chassis either screwed together, touching or clipped to complete grounding.
I don;t know about other models and grounding, ceratinly a lot of PV gain controls are feedback resistances on op amps and not grounded at all. On this amp, the master is a conventional voltage divider with the lower end of the pot grounded, but the channels use a feedback system, and the WIPER is grounded.
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