I have an LMIII. It's about 3 years old.
I've done at least 250 gigs on it.
Love the amp.
Last weekend I plugged in and I had to crank it to get any volume.
Tried different cables and basses.
I usually set the gain on 3 and the master on 4.
Now I've got to crank the master all the way up.
What's also odd is it seems to slowly gain power some power back over time.
IIRC MarkBass set the effects loop to parallel as default so leaves out the normal effects jack trouble. It could be a corroded interconnect cable inside the amp (like a ribbon cable). Other than that I don't have much knowledge of their design.
Just call me B-String 2
GK Club #488 Big Cabs #175 Peavey Amps #92 50+ Club #44 Grumpy Old Fart #2