Marshall MG100FX Issues with gain control when switching channels.

[Labjr]

A friend brought his Marshall MG100FX amplifier in. Made in Vietnam model. Has an issue where the volume drops way down when switching from clean to crunch. As soon as I adjust the gain even slightly it jumps right back to normal. When switching from crunch to clean it's fine. Only when switching back to crunch and it happens every time. I removed the gain pot and cleaned it with Deoxit but it didn't help. I suspect it's a problem with switching. Maybe a analog switch IC. I don't know. I can't find a schematic for this exact model.

I've read about the exact issue in other forums. I'm thinking it's not worth the time to troubleshoot this.

 

[fitz]

Has an issue where the volume drops way down when switching from clean to crunch. As soon as I adjust the gain even slightly it jumps right back to normal. When switching from crunch to clean it's fine. Only when switching back to crunch and it happens every time

Are you having the issue with the amp set on manual mode?
You might be describing the channel switching to a low volume preset that is overridden with a manual adjustment when you change a knob setting.

 

[Labjr]

The amp initially had a problem with the input jack. L6 was burned on the little input PCB. I just shorted and it started working execpt for the gain problem. I was ready to give up. I'm not real familiar with DSP stuff. I stored the settings and it's working fine. Thanks for the tip.