I have a Randall RG1503 on my bench. Amp works fine manually switching but the footswitch does not change the channels. My customer has a RF4G3 footswitch. Has the right cable but is this compatible with this amp? If so where should I be checking for faults? Footswitch does work when I check continuity on the individual switches. Looks like an IC controls the switching in the amp vs relays.