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This amps frontpanel switching works, but not the footswitch. I've eliminated the footswitch as NOT being the issue. I tried a shorting plug and an unshorted plug and neither changed the channels. My head hurts (per usual) from looking at this schematic... I don't like Marshall's schematics. Anyway, it seems as though the footswitch jack on the back of the amp works like this: tip grounds the junction of R30 and other components, ring grounds R13 and other components. What I can't wrap my brain around is this: It seems as SW1a and SW2a also do the grounding of those same points - so how does plugging in the footswitch disable the frontpanel switches? Finally, even w/ an unterminated phono plug in the footswitch jack, the tip is showing as grounded on my meter.
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So the panel switches work, that means the whole switching circuit works.
The FS is in parallel with the panel switches, right? So find out where the loss of continuity is.
Plug in a footswitch, and make sure the panel switches are in the open position. Now AT THE CIRCUIT, or at the panel switch if that is convenient, measure continuity to ground as you switch the FS off and on. Does continuity come aqnd go with the FS action? If this does not happen, then there is an open in the FS jack circuit. If neither button works, then I'd suspect the "ground" from the FS jack. Start there, is there continuity to ground from the sleeve contact of the FS jack? Do the two tip and ring contacts show continuity back to the panel switches or the switching circuit? There is the FS jack itself, its solder connections, and the 10-wire cable back to the main board with solder connections at both ends. And ther are traces on the boards to complete the circuits.Education is what you're left with after you have forgotten what you have learned. -
cool yeah I didn't realize that both frontpanel switches had to be pushed in to be open and allow the footswitch to do the grounding. I skimmed the manual and didn't see anything that said to do that but maybe I missed it. Turns out the OD1/2 was intermittent due to a bad footswitch cable... all good, thanks.Comment
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LOTS of amps require the panel switch be set one way or the other for the FS to work.Education is what you're left with after you have forgotten what you have learned.Comment
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