During checking last night, (which didn't yield much - the stomp
switch actually is working), a wire broke.
This is the yellow wire (18v) from the wall wart jack that connects to
a pad on the PCB (see the solderside photo link.), which in turn
passes thru the 741 opamp, and then passes to an electrolytic 10uF
cap.
Once I re-soldered the wire, I was checking the 10uF electrolytic cap
that is fed from that yellow wire,
and found voltage on one side, but not the other. Unsoldering it and
checking continuity I found it open.
But, capacitors aren't just used for coupling signals (and blocking
DC), they are also used to bypass and filter. When they are bypassing
and filtering, one side in the circuit is usually going to ground,
so not finding voltage on the other side means nothing.
And capacitors will not show continuity between terminals, at least
not after a brief time (the length of time dependent on the value
of capacitance, the more there is the more delay).
If this is the 10uF capacitor connected to the arm of the 100k "trim"
pot, then all it's doing is keeping noise off that point, and one
side is indeed grounded. That capacitor not working or not being
there will not cause the unit to fail, at best there will be noise.
The trick to troubleshooting is to find the general area, and then
narrow down the fault. Just going through components will take
forever, and is open to misinterpretation since in circuit
they may appear different from when they are outside the circuit.
You don't want to have to desolder and resolder every component
finding this problem.
So you look at the collector of that 2N5037 connected to that 741.
If there's the right voltage, the schematic says 12volts, then that
section cannot be the fault. If there's no voltage there, then
something before that point is not right.
If the proper voltage is there, you need to look elsewhere, looking at
the unit as multiple stages and seeing where the DC voltage disappears
or where the audio signal disappears.
Michael
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