Pardon my ignorance, but I don't understand

[01redcobra]

I'm sure this is minor league for most of you techs, but can anyone explain to me how the channel switching on this Epiphone socal 50 works? I suspect it has a bad relay, but don't understand this schematic. Thanks in advance.EpiphoneSoCal50.zip

[Enzo]

Sure, you plug a two button pedal into the footswitch jack. Then step on the one button to turn reverb on and off. Step on the other button to turn overdrive on and off. That's it.


BWAAAhahaha.

OK, the two functions are both relay switched. I cannot tell which is tip and which is ring on the jack, so we'll ignore that. Pin 5 of the jack is at the top. It contacts some part of the plug on the FS. The FS switches that pin to ground or not. That completes the circuit through the parallel coils of RLY1 and RLY2. Point F is a 12v DC supply also used by the preamp tube heaters. Look at RLY1 contacts. It is a DPDT, and should eb shown in its relaxed state. The right side contacts simply connect +12 to either of the two LEDs, D1 or D2. The left side contacts ground the grid of V1b when energized. This silences the dirt channel when in clean. AS drawn, it is in the dirt channel mode.

Now look to the right to RLY2. It energizes at the same time as RLY1 since their coils are parallel. Look at the DPDT contacts. They select the signal from either VR1 or VR4 to pass along to the grid of V2b, pin 7. As drawn, the left side is grounding the clean volume VR1 signal, wwhile the right side is completing a circuit from VR4 to V2b. If that relay energized, then it flips, and VR4 would be grounded and VR1 signal passed along to V2b.

So really all that channel switching does is ground the unused channel and pass the used one along to the rest of the amp.

The other relay, RLY3 is controlled by pin 4 of the jack, and the relay contacts just ground off the reverb return or not.

When you are NOT using a footswitch, the cutout contacts on the jack add in the panel switch for channel change. And as clumsy as it is drawn, it just grounds pin 6 of the jack or not.

If your amp won;t change channels, first place I look is a bad contact between pins 5 and 6 of the FS jack. or a bad switch. If the amp won;t switch with a footswitch plugged in, then open the FS and measure voltage. There will be two switches in the FS, one side should be ground, and the other side connects to the relays through the cable and jack. You should get 12v and zero volts as you click each switch off and on, measured at the switch..

If the relays don't want to work, check for voltage there. The coil terminals can be hard to get at, but there is the diode D3 in parallel with the coils. You can probably find that next to one of the relays, and get a meter on it. Got 12v? One end should stay at 12v, the stripe end. The other end of the diode should change from 12v to zero volts as you click the switch.

[01redcobra]

Thanks so much for the education. Since my stroke a year ago, some things just leave me baffled. Your reply helped put everything in order for me.
Checking everything, I've found that the relay must be a goner. I get all the voltages switching (and grounds) except it doesn't switch the leds as it should. And pins 3,5, and 7 all are grounding. That would explain the customers complaint that the channels bleed over into each other! Now all I have to do is find a relay and put it in. Ugh. Thanks ever so much Enzo! You are the man!