Mesa Boogie Nomad 100 amp, 2001?

[N_Cook]

Phantom channel change, randomly. Was with footswitch board only, they
then used the rotary sw on the rear and now that is playing up.
I'm assuming like the notorious Fender footswitch problem, but will it
be drift of R values here as well, or ps/Vreg failing rather than the
internal Vreg of the weird LM3914 bargraph driver use (no bargraph
display) causing problems and just reflecting faultmode varying
analogue Vs .
What is the function of that 3914 if the relay switching points are
determined by voltages,Rs and zeners

 

[N_Cook]

Looks as though the LM does decode/determine which ch relay is on.
So monitor input V on p5 with different footswitch and rotary sw
settings and then a muliturn pot instead, to see what voltage window
does what. dot1 output for ch1 relay,dot3 for ch3 relay and ch2 must be
absence of dot1 or dot2 signal.
Hopefully +1.8V, -3V or LM Vref is moving around, to explain both
footboard with all that TTL and rotary sw now causing the same problem.
Also check whether 2 channels are ever on together

 

[N_Cook]

Problem with the integrity of the grey ribbon IDC link between main and
rear boards