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Recently picked up a Peavey Series 260 Monitor Amp that has problems. It is showing 38V DC on the outputs. Condition appears with or without a load. When loaded, I'm using a 5 ohm dummy load and not a speaker.
Here is what I have checked:
Output Transistors: 4 -- RCA 62792's. Checked ok. Even replaced them with RCA 2N3055's with same results
Filter Cap: tested ok. Shows 38V on each cap. Switched to AC test and voltage was negligible.
Cement resistors: 5 -- .33 ohm cement resistors test fine.
Diodes: all diodes test fine. Those that did not were removed from circuit and tested fine.
Other resistors: All test within specs
Transistors on Heat Sinks: marked EP430 and EP431. Removed from circuit and test fine.
Second EP430 on board tested fine.
Other transistors: 2N3642, 2N3638, SPS761, GE82 all removed tested fine.
All other capacitors on the amp board removed and checked. All check ok.
Bringing the amp up on a variac without a load shows very little current draw on the AC line. With a load and going up to about 100VAC on the line, the amp draws about 2.5 amps. I shut it down before the fuse blows. In either state, there is DC on the outputs. The above is true with or without the preamp section connected.
The amp shows signs of being previously worked on.
I am working a bit in the blind in that I do not have a schematic. If anyone has one they can post, it would be greatly appreciated.
Any ideas would be greatly appreciated. This is a mystery to me.
Here is what I have checked:
Output Transistors: 4 -- RCA 62792's. Checked ok. Even replaced them with RCA 2N3055's with same results
Filter Cap: tested ok. Shows 38V on each cap. Switched to AC test and voltage was negligible.
Cement resistors: 5 -- .33 ohm cement resistors test fine.
Diodes: all diodes test fine. Those that did not were removed from circuit and tested fine.
Other resistors: All test within specs
Transistors on Heat Sinks: marked EP430 and EP431. Removed from circuit and test fine.
Second EP430 on board tested fine.
Other transistors: 2N3642, 2N3638, SPS761, GE82 all removed tested fine.
All other capacitors on the amp board removed and checked. All check ok.
Bringing the amp up on a variac without a load shows very little current draw on the AC line. With a load and going up to about 100VAC on the line, the amp draws about 2.5 amps. I shut it down before the fuse blows. In either state, there is DC on the outputs. The above is true with or without the preamp section connected.
The amp shows signs of being previously worked on.
I am working a bit in the blind in that I do not have a schematic. If anyone has one they can post, it would be greatly appreciated.
Any ideas would be greatly appreciated. This is a mystery to me.
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