On 14/10/2015 16:18, wrote:
Hello,

I was wondering if you could help repair a guitar amplifier, it is a
Fender Frontman 212R, schematics are he
http://support.fender.com/schematics..._schematic.pdf

The problems a
-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.


Is there a send/return pair, that you can put a test signal in the RET
to narrow to PA or PREA.
Suddenly happen or previous intermittant level change?