Troubleshooting really strange problem in Microamp

[studiostud]

I have a weird problem that I'm trying to troubleshoot.  I have a Microamp circuit that I originally had working fine.  I unboxed the circuitry to paint and finish it and when I re-housed everything is when the problem started. 

When I have the 3PDT in the on position, signals gets through to the circuit and then I traced it until the last 470 ohm resistor.  The resistor ohms register fine with a multimeter but no sound is getting passed, even on the outgoing lead so it's not a soldering issue.  But that's just one problem that I hope is related to the other.  The other problem is that when the switch is in bypass state, I don't get any signal and the weird thing is that I have a tone generator plugged into the input jack to give a constant signal to probe with and when the switch is in bypass mode, it kills the signal even at the input jack.   what the heck?!  the continuity in the wiring seems fine and I when I unhoused everything before, I didn't unsolder anything except the power jack and I re-soldered that the same way when I re-housed so I don't think it's a wiring issue or a matter of the switch flipped 90 degrees. 

My guess is that it has to have something to do with the power/gnd path and not the signal path because continuity-wise, the signal path checks out. 


Any ideas? 

[KazooMan]

It sounds like something you did has shorted the output jack.  Occasionally you get a cheaply built jack that can even short out just be over tightening the nut.  Check for a short at the jack with your DMM.  

[studiostud]

thanks for the tip!  I actually figured it out on a whim by testing a random idea just to eliminate it from the possible problems.  It ended up being that the 3PDT was shorting.  I didn't have any sort of a nut or washer between the switch and the inside wall of the enclosure and that contact must have shorted it.  I put the plastic washer that came with it on the inside and the problem went away.  Still a little confused as to why this problem existed since I almost always put the plastic washer on the outside, but I'm glad the problem is fixed.

If you have the knowledge as to why it happened, I'd love to hear it.  Anything to make future builds easier to troubleshoot it always helpful! 

THANKS!

[Bad Chizzle]

Hi,

Wow, that's weird! That's a new one to me.

Glad you got it fixed though!

[KazooMan]

That is very strange.  I assume that you are using the usual 3P2T switch like the ones from Smallbear.  If you are using some other brand of switch my comments may not apply.  I just checked to be certain and confirmed that the "plunger", threaded tube, and the metal flange that crimps onto the plastic body are all connected electrically.  Therefore I can't understand how the plastic washer on the inside would make any difference.  If there is an internal short of one side of the switch to the shell, or you have somehow managed to create a short with a small end of one of the wires or a solder bridge, then it could short out the signal.  The only way I can imagine that the plastic washer would make a difference is if you have paint providing insulation between the nut and threads and the case.

With the pedal operating (bypass or effect) try bridging the metal parts of the switch to ground.  If the signal dies it would show that there is some sort of problem inside the switch or with the wiring that is creating a path for the signal to the metal part of the switch.  This would cause a failure down the road it the paint insulation wears through.

A more plausible explanation is that a stray end of wire on he output side of the switch was creating a path to ground and it was fortuitously fixed when you moved the switch to install the washer.

Glad you got the pedal working.