Fender M-80 112 non chorus channel bleed

[g1]

Then try what Helmholtz suggested, a pair of series 1N4148 in place of each LED.

[jvm]

Then try what Helmholtz suggested, a pair of series 1N4148 in place of each LED.

Would there be any difference in that and replacing the LED's, g1? The two I installed are the same part number as what this amp had in it according to schematics. Do you think the 1N4148's might behave differently?

[Helmholtz]

The 2 Leds would have to be replaced by 4 (or 6) 1N4148s.

Actually I can't think of a reason why LEDs would "radiate" more signal than the standard diodes - apart from emitting a little modulated light.

Signal transfer via modulated light is possible but would require some light sensitive component in the power amp.

[jvm]

The amp is usable with the LED's bypassed. It had no shortage of gain to begin with and the volume and gain reduction in the drive channel is really not that significant. Still plenty of gain and level It's not worth investing more time into this amp. I appreciate your help g1, Helmholtz and Enzo.

[g1]

A couple more things to check/try if you want to get back into it sometime.
Two schools of thought about the problem:

a) it's a fault and the unit did not do this when new.
If this is the case, the only other thing I can think of is that there is way too much gain/level in the circuit due to a fault. Then there would be way more signal through U2A, resulting in the bleed through.
It would be worth your while to check the AC signal levels at TP8,9, &10. AC voltages are listed in the ovals. Test conditions in the notes are 5mV 1KHz input at J1 TP7, gain set to 9 o'clock and other controls set to 12 o'clock. Verify that AC voltages TP8,9,10 are in the ballpark of those listed. If way high at TP10, find the problem.

b) it's a design flaw and was a problem for all units of this model.
This is what I've been inclined to think, and I have vague recollection of the issue when this model was current. But I may just be imagining that so haven't mentioned it earlier.
If this is true, you could try putting a regular single diode (ex.1N4148) in place of each LED. This will give more gain than the jumper wire, but less gain than the LED. From there (if successful) you could try 2 series diodes for each LED. Somewhere you may find a compromise between gain and bleed through.

[DrGonz78]

What would happen if the grounding mechanism in the foot pedal jack was a bit dirty?

[DrGonz78]

Looking at the schematic closer I see that my question is not valid. I get that certain pins on the IC get grounded out when flipping the channel switch. My idea was that the ground connection to pin 4 when switched might not be getting a fully grounded connection. Probably not what is wrong but just had to put it out there.