Marshall 8100 low and distorted/fuzzy both channel help please

[yustech]

Hello all,its me again.My apology

I'm troubleshooting this unit.Its distorted both channel.The output is low too.This is a second unit.I failed the first one last year.I gave it back due to my lack of time a.k.a I'm slow.

The problem come and goes.Feeding to return seems ok and I think it the preamp but I don't know where.I feed a 440hz sine wave for tracing on a on and off basis as the reading on my scope is ok(I think).Plugged in the guitar to play and trace at the same time is hard to do but that's when the problem can be heard.Is there a common spot at the PCB to focus on about this symptom.?I as much like to solve this with the help of you guys.My Marshall success repair is low.Trying to get back doing it good again.My amps encounter has few and much fewer when I started to do more guitar repairs.Those pays the bills quicker than amps.Hope most of you with such experience could give me pointers.


Thank you

[phatt]

Before you go further a simple test first.
Bridge the FX loop with a working guitar cord,, any difference?
Phil.

[yustech]

OK Mr Phatt,will do that.Will be back.