TSL100 footswitch mishap

[Teleman55]

I was going through this amp for a friend to make sure it was running,the footswitch DIN connector had been pushed in.I repaired that and plugged in the footswitch that was supplied.I noticed no channel switching functions worked,and no volume followed by the smell of burning electronics.I found R21 a 100R resistor burned,sure enough it is part of the ftsw circuit.It was then that I noticed that on of the switches on the ftsw was for chorus.I gotta figure this caused a short,Can this ftsw be properly wired? where can I find a schematic if it can be rewired?

[Teleman55]

While I was at it I checked the bias on the three pin connector What would be a good range to set the bias,I had 94mv on one pin and 44mv on the other.

[Ray Ivers]

Here's a partial print for the TSL100 footswitch circuit inside the amp (R21 is at the bottom):



My own troubleshooting procedure would most likely consist of measuring each amplifier DIN-socket pin for proper voltage, opening up the footswitch and checking it out thoroughly for mods/problems, etc. You'll have to chase out CONs 5, 6, and 7, so here's a link to the entire print:

http://www.schematicheaven.com/marsh...sl100_100w.pdf

I've seen these amps go into thermal runaway with a hot bias point, so I'd recommend 50 to 60mA (50 - 60mV) at each test point - but obviously do as you see fit.

Ray

[Teleman55]

Thanks Ray; I returned the amp after repairing it and recommended getting the proper foot switch.I set the bias at 68ma.I also checked the EL34s with an IR thermometer.I measured temps of 315-315-410-198.I also suggested a new set of tubes.