So on the 388, generally speaking, if your stereo and monitor L-R outputs work fine until you latch one or more of the channel 1~8 L-R assign buttons, it’s *usually* a failure of the U104 switching chip on the...crap...monitor PCB? Buss B PCB? I can’t recall off the top of my head now at the moment. But it’s a 4000 series logic chip that seems to eventually go bad on the 388, at least I’ve encountered either personally or assisted others with the problem a dozen or more times in recent years. This is the chip that allows the L-R assign buttons to double as a solo-in-place function, muting other signals assigned to the L-R buss such as the monitor mixer, etc but allowing other “L-R” assigned signals through. I’ll refresh my memory which board that chip is on as soon as I am able, unless somebody else can recall sooner. But that would be my first strong hunch if your problem doesn’t arise until you latch one of those L-R assign switches. I believe the chip is still readily available, and it’s a low-cost part, and an easy fix if you or somebody you know is comfortable desoldering a DIP IC and soldering in a new one.
