I have a DSL40C and bought a used 90012 model footswitch. Turns out that switch is meant for the newer DSL40CR. It is tip and ring with two sleeves for the two buttons, but the channel button does nothing. When plugged in the channel button on the amp no longer works, yet the footswitch button does not change the channel either.
If you pull the footswitch half way out it causes a channel change.
So the question is, does the amp have an issue or is this footswitch just not compatible? It's a two button, tip and ring with two sleeves so in my mind it should work...
Some internet sloothing leads me to a model P802 footswitch that was the one for the DSL40C amp but it seems like the same switch to me...
The pedal you need for your DSL40C is PEDL-91004 two way without LED.