Tweet
Hello All,
I am trying to repair this amp for a friend of mine. I haven't worked on many solid state amps so please excuse any ignorance I may have. I have built and worked on quite a few tube guitar amps and I have a good arsenal of test equipment. I also have the correct schematic for the amp.
I have isolated the problem this amp is having to the power amp. I have unplugged the 2 molex connectors from the front panel and am running a test signal into the power amp in. I get a faint sound that fades in and out every couple seconds or so. I am getting +/- 52 volts on the main voltage rails and +/- 15 volts on the molex pin connector going to the preamp. I have checked for shorted caps and tested the diodes with my DMM. I have read about the op amps (U1 & U2) but have no way to check them. Just for the heck of it, out of frustration, I took the output from my sig gen and touched it to pin 13 of op amp U1 and the amp came to life. Very loud sound from the speaker that followed the sound coming out of the sig gen which leads me to believe that the main part of the power amp is working. I am not familiar with what these op amps really do so I thought I would replace the U1 amp which is a TL074CN. It didn't do the trick. Same problem. I am wondering if it might be the other op amp U2 which is a 87478. Does anyone have any ideas of anything to do or voltages or components to check which might help me fix this thing? I would greatly appreciate it if someone would please help me out. Thank You!!
I am trying to repair this amp for a friend of mine. I haven't worked on many solid state amps so please excuse any ignorance I may have. I have built and worked on quite a few tube guitar amps and I have a good arsenal of test equipment. I also have the correct schematic for the amp.
I have isolated the problem this amp is having to the power amp. I have unplugged the 2 molex connectors from the front panel and am running a test signal into the power amp in. I get a faint sound that fades in and out every couple seconds or so. I am getting +/- 52 volts on the main voltage rails and +/- 15 volts on the molex pin connector going to the preamp. I have checked for shorted caps and tested the diodes with my DMM. I have read about the op amps (U1 & U2) but have no way to check them. Just for the heck of it, out of frustration, I took the output from my sig gen and touched it to pin 13 of op amp U1 and the amp came to life. Very loud sound from the speaker that followed the sound coming out of the sig gen which leads me to believe that the main part of the power amp is working. I am not familiar with what these op amps really do so I thought I would replace the U1 amp which is a TL074CN. It didn't do the trick. Same problem. I am wondering if it might be the other op amp U2 which is a 87478. Does anyone have any ideas of anything to do or voltages or components to check which might help me fix this thing? I would greatly appreciate it if someone would please help me out. Thank You!!
Comment