stevem Messages: 4738 Registered: June 2004 Location: NY
Senior Member
I do not have a schematic for that amp, nor does this site so I need to ask if that 5129 is the driver board with the square Transistor heat sinks on it and box style 5 watt resistors, or is it a preamp board?
Also if you hook up a voltmeter set for D.C. Volts to the amps speaker output do you read any voltage?
Do you mean that the preamp board is not passing signal?
Check the two power supply voltages. Then read the voltages at the outputs of the preamp chips. There normally is no (or little) voltage on the output pins.
sunnhead Messages: 221 Registered: June 2010 Location: Minnesota
Senior Member
The amp was used to play a stereo through before I got it. Im sure the person blew the transistors out plugging in the stereo. The preamp signal is just hum, and increases hum when turning the reverb pot up. The board has 2 IC chips, unsure if they are damaged. I would like to rebuild with new transistors and maybe the IC chips. Looking for a parts list to order up the parts.
That board should have 3 ICs. Only 2 of them will stop the signal from passing, I1 and I3. I2 which is a dual opamp is used for the reverb driver and for the trem low frequency oscillator.
Yeah, that's the right board. I1 has been replaced earlier and a socket has been added.
I2 is the 8 pin 1458 in the center of the board and I3 is the round TO-5 (I think) one near the edge of the board. I3 is a house numbered LM3080 transconductance op amp.
Check transistors T1 and T2, then check for dc voltage on the in/out pins of the 3 ICs.
sunnhead Messages: 221 Registered: June 2010 Location: Minnesota
Senior Member
Ok so The amp is now fixed, turns out one of the ziner Diodes failed and was putting 40 volts into the board. Replaced that now the board gets the 12 volts. The bigger IC was fried replaced that. Amp is working great now!