Hot Rod Deluxe channel switch problem

[Brad1]

My friend's Hot Rod Deluxe no longer switches channels. He said when he pushed the control panel button last week, it seemed like it was switching back and forth quickly, the LED flickered with it, and then it just stayed where it stopped, which is the LED is off.

The amp still works fine, as far as playing it through that one channel.

I used the footpedal switch from a DeVille to test it, figuring that maybe the panel switch was whacked, but the pedal might work. No go. The foot pedal LEDs both change (channel and drive) but nothing happens in the amp.

Apparently, the "More Drive" switch isn't functioning either, but is that because it doesn't work unless the non-working channel is kicked in?

Having looked at the schematic, I see that both switches are in the same circuit. What I can't figure out, yet, is how exactly it works. I assume that circuit somehow switches the relays (K1 & K2?) to change "channels" and kick in "More Drive"? I am also guessing that since neither seems to work, it may not be the relays, but something in the switching circuit (that is disconnected schematically from the main circuit)? I'm trying to follow the logic through this thing, and am not even sure, yet, if those relays do a task each, or both work together. If the More Drive circuit isn't engaged until that channel is engaged, I suppose a bad channel relay would prevent both?

Anyway, before my head explodes, has anyone run into this before, or does anyone have an idea of the (or some of the) likely culprits that may cause this?

Thanks in advance.

Brad1

[Don Moose]

This is a _very_ common problem with the whole HR line.
Search for topics including HR Deluxe, HR Deville or Hot Rod and Channel.

[52 Bill]

Check the low voltage supplies for overheating dropping resistors and also check to see if the led is broken loose from the circuit board.

An over simplified explaination of the switching system is that there is an ac voltage on the ft switch line. The ft switch causes either a positive dc or a negative dc voltage, which the amp uses to turn on and off the channels, reverb, etc.

[Brad1]

Thanks guys. It was a trace connected to R78. I didn't have the thing here when I first asked, but brought it home this afternoon, and with a few tips, it made sense. Repaired the trace, and good as new.

Thanks,

Brad1

[trem]

Good catch sir. Well done!