Solid State Guitar Amp Forum | DIY Guitar Amplifiers
Solid State Amplifiers => Amplifier Discussion => Topic started by: smilan on October 03, 2024, 12:53:51 PM
Hi,
I have a Fender Frontman 65-R with distorted output.
I need some help troubleshooting this amp.
The output from the "PRE OUT|" is clean so the problem is somewhere on the power amplifier.
The signal seems to be OK at pin 3 of U-7A but at the output of this op amp (pin 1) the signal is very distorted.
With Q6 disconnected, the output on pin 1 of U-7A is clean.
I took out Q6, tested it outside the circuit and it tested good.
What should I test next?
(https://i.ibb.co/4ZWHYFG/65r.jpg)
Here's the schematic:
(https://i.imgur.com/Wk3yiRC.png)
The differential pair of Q6 and Q7 are a very common problem in this series of amps.
They need to be well matched and will fail in ways that do not show up in testing on your meter.
I think you have already localized the problem to this area so you should just go ahead and replace them, then continue troubleshooting if the problem is not solved.