SOLVED Basic Relay Bypass switching LED but not passing signal

[rhaas]

Up until today, I've used the Basic Relay Bypass (latching) on at least 15 pedals without issue. Up until today...

For some reason, the first board + switch that I assembled would switch the LED but not pass signal when turned on. Things I checked:

1. All solder joints are solid, and there are no solder bridges.
2. All resistors and capacitors are the correct value.
3. The 2N3904 and 2N3906 transistors are in the correct place and in the correct orientation.
4. The NE555P and relay are in the correct orientation.

I wired the input and output jacks directly to the effect PCB just to make sure that wasn't the issue. It worked fine.

So I figured that maybe I accidentally fried the IC or relay during assembly (I was admittedly in a hurry) and went about assembling a new one. I was really careful this time, soldering only two pins at a time on the IC and relay. And I was especially diligent about inspecting all the solder joints. I wired it all up and... this one does the exact same thing.

I'm really tempted to just throw in a 3PDT and be done with it, but I'd love to understand what's happening. Any troubleshooting tips to pinpoint what could be wrong?

 

[jwin615]

Are you sure the PCB is passing signal?

 

[rhaas]

Are you sure the PCB is passing signal?

The effect PCB or the bypass PCB? As a test, I wired the jacks up to the respective IN/OUT pads on the effect PCB and it was passing signal.

 

[Robert]

Does the LED switch on and off like it should? (Not just come on and stay on)

Do you hear the relay clicking when you press the footswitch?

Does it pass signal in bypass?

 

[rhaas]

Does the LED switch on and off like it should? (Not just come on and stay on)

Do you hear the relay clicking when you press the footswitch?

Does it pass signal in bypass?

Yes to all of the above!

 

[Robert]

Do you have a DMM?

If so, apply power and switch the pedal on, then check for continuity between:

Input jack tip and effect PCB IN pad (You want continuity here)
Output jack tip and effect PCB OUT pad (You want continuity here too)

Input jack tip and ground (You do NOT want continuity here)
Effect PCB IN pad and ground (You don't continuity here either)

Don't poke around in there too much with power applied since you'll be in continuity mode.

 

[rhaas]

Input jack tip and effect PCB IN pad (You want continuity here)
Output jack tip and effect PCB OUT pad (You want continuity here too)

Input jack tip and ground (You do NOT want continuity here)
Effect PCB IN pad and ground (You don't continuity here either)

Thanks! Not sure why I didn't think to do this. All of these check out, so I'm not sure how it's not working now when it was working in my "hardwire to ON" test.

I did remove and reinstall the effect PCB when I replaced the relay board, so maybe something on the effect PCB is intermittently shorting? My first thought would be a short against the back of the Filter pot (it's a Muroidea) but I have a plastic dust seal cover on that...

 

[rhaas]

Okay, I finally had the presence of mind to measure the opamp voltages and I noticed 0 volts on pin 7. I reflowed all the opamp pads and now it's working again! My best guess is that one of those pads had a poor solder joint and the connection was intermittent.

Sorry for overlooking the basics! Life has been chaotic lately and my head wasn't in the game on this build.