Super Champ XD footswitch/channel problem

[allprobbob]

***Quick bio - former electronics/radio tech and lifelong tinkerer. That said schematics and voltage chasing was never my strong suit. More of a "poke at it until it works, or the genie shows up" guy lol.

Got a super champ xd, really like it so far (2 weeks in). Ordered a used footswitch off ebay and finally tried it out, no joy. Been testing and checking everything, starting to get hangry and overly irritated. So I thought I'd fire off a flare and see if anyone can help before I make some food, and start re-assessing. Here's where I'm at/what I've got atm.

When I plug in a cable (1 speaker, 2 instrument, all tested good) to FS jack OD channel is lit, this happens regardless of having a FS connected.
When I do plug in the FS I can toggle the channel select LED by toggling the switch, but it has no effect on the amplifier channel.
The Effects LED does not illuminate when switch is toggled, will illuminate with direct power applied.
I have gone point to point on the FS PCB and all seems in order, switches have continuity when they should and vice versa.

I found a post that suggested a similar issue was fixed by re-flowing the ribbon connectors between the main board and pot board, I tried this and performed basic continuity testing while I had the amp open/apart. Again I couldn't find any glaring defects, the channel switch circuit seems to be sound, and my problem persists.

I have 12v coming out of the FS jack/cable.

Anyone have some experience or tips, or test values, etc? I may be missing something simple, and I know I haven't done a complete bench test, but I'm really hoping to avoid that and start playing again. Any and all help is appreciated folks!

[nosaj]

Are you using a TRS cable or just an instrument cable? Pretty sure you need TRS.
nosaj

[allprobbob]

I was extremely curious about that. Schematic shows TRS at amp, but TS at footswitch. Schematic says "Use standard 1/4" instrument or speaker cable" Don't have a TRS around atm. ugh

[dmeek]

Check the voltages at TP11. From there it goes to a 4051 multiplexer chip and on to the DSP board. Hopefully the problem is before TP11.

[g1]

Ring is shorted to sleeve at amp jack so you only need regular mono TS type cable.

[nosaj]

Does channel switching work on the faceplate?
nosaj

[allprobbob]

Note: Amp works fine unless FS is plugged in. With FS I only have channel 2 (effects function as normal regardless of FS presence or Effects selection).

Ok, I ran voltage tests.

+12.08 @Tip with no FS attached

+4.08 @TP11 with TS cable plugged into FS jack

NO FS (panel operation) @TP11 - Ch1 +2.97 Ch2 +3.67

@TP11 With FS

SW1 SW2
open open +4.08
open closed +4.08
closed open +1.64
closed closed +1.64

I realize these numbers do not jive with the specs, but am at a loss as to why without many hours reviewing very thick books on my shelves.

[g1]

So the good news is the problem is before TP11 and not some digital problem like dmeek mentioned.
Go back and do TP10 measurements.
And please confirm panel switch works when footswitch not connected.

[allprobbob]

Yes amp works normal, channel switch on front panel functions properly. Malfunction begins when cable is plugged into jack regardless of FS being attached or not.

[allprobbob]

No FS cable - Ch1: +2.03 Ch2: +2.62

Cable plugged in no FS +3.05

SW1 SW2
open open +3.04
open closed +3.04
closed open +0.78
closed closed +0.78


It's all coming back to me. Getting coffee and moving on down the list of TPs, sigh...

[g1]

It is normal for the amp switching to not work right if cable plugged into FS jack but no footswitch.

As amp is working right with panel switch, most likely it is fault in footswitch (or wrong footswitch). Assuming you have verified that it is correct FS for this model, did you check the 2 non-LED diodes in the footswitch? Check for any bad solder? You mentioned both LED's are good, but bad solder is still possible.

[allprobbob]

It's an older footswitch no PN on case, inside stamped 1989, "P/N 028445 C" on PCB. Appears to be a 0071359000. From the schematics I've pulled it looks to be correct, and when I searched the number on the PCB all I could get for results lead me to believe it's the 0071359000. Can anyone verify if I even got the correct FS? I've checked all the joints/solder points, it seems to have voltage and continuity where it's supposed to. I've pulled the diode on the non-functioning side tested and replaced(just to see) and it's the same behavior on the amp. I understand that the FS overrides the channel select on the amp, and having an open FS circuit(jack not connected to FS) can make for weird behavior. Is it normal on this particular amp for an open ended FS cable to auto-select CH2? I'm going to order a NIB FS just to be sure, but this is going to fester until it arrives. This is what I get for trying to save a few bucks...

[g1]

Sounds like the right one.
With a cable plugged in to amp's FS jack, but no footswitch, the jack's tip to tip-switch contact is opened (Q1 collector to D17 cathode). That it then switches to Ch.2 seems reasonable.
With footswitch all connected and both switches 'open', measure DC volts from FS jack sleeve to the points listed:

[nosaj]

Just a thought where the cable plugs into the amp slide it out just a bit maybe 1/4 inch an see if part of pedal switches. I've done this when I didn't have a TRS cable just to see if switching works. Of course First off check continuity on the cable to verify cable is fine.
nosaj