Peavey Classic Chorus 212 channel switching problem

[jvm]

I have a Peavey Classic Chorus 212 that does not switch to the drive channel. No footswitch but does not change channels when using front panel switch. Power amp and clean channel work fine. 706.pdf

[52 Bill]

Did you test the panel switch?

Check Q4 in the switching circuit. It is the ground path for the relay. Test it to be sure that it is okay and that there is +15 volts dc on it's base to turn it on.

[Enzo]

Agree, Q4 is the ground path for the switch, when there is no pedal. You can short the collector to ground to test the circuit.

R61 is a pullup resistor to +15v for the base. However, you won't see +15 on the base, or at least you shouldn't. You should see more like +0.5v, the base-emitter junction voltage.

If that is OK, and the switch actually works - check it with an ohm meter - then see if there is 15v on the relay diode CR15 - on both ends, and also check if R171 is open.

[52 Bill]

R61 is a pullup resistor to +15v for the base. However, you won't see +15 on the base, or at least you shouldn't. You should see more like +0.5v, the base-emitter junction voltage.

Caught me again. I really should pay attention before posting. I'll go back to my room now.

[Enzo]

Oh, other than the amount of it, the tip to look for a positive voltage on that base is valid.