Hello,
I was wondering if you could help repair a guitar amplifier, it is a Fender Frontman 212R, schematics are here:
The problems are:
-Low volume. It is a 100W amplifier and at full power is delivering something like 20W tops at max volume.
-Paper crackling sound when guitar is played very hard. It is very subtle, but is annoying.
I know that:
-Power supply voltages are ok (including the power amp stage)
-Speakers are ok (it has two speakers of 8 ohms in parallel as load)
-Nothing seems to be burnt on the PCB, or any cap seems bloated or something
It is unknown to me what the PTC (RT2) is doing, I know the NTC (RT1) is for mains thermal shutdown, but the PTC seems to be for thermal shutdown of the power stage only (because it is thermally coupled to the power transistors power dissipator with some paste).
The next time I see it I will try to see if it is a pre-amp problem or a power amp problem (because fortunately it has a pre-amp out and pwr amp in)
Thanks.