Op-Amp Muff was working, now no sound in bypass or engaged (FIXED)

[lincolnic]

Hey guys.

I finished up Jacob's Op-Amp Muff last night, and did a quick test before I had to run out the door - no knobs or backplate on the enclosure, but it sounded great. Today, I put knobs and the back on to test it for real, and the LED lit up, but suddenly I had no signal when the pedal is engaged or in bypass. It was a bit of a tight fit, so I figured maybe something was shorting out against the backplate. I covered the inside of the backplate with electrical tape, and also a few spots on the bottom of the PCB where it looked like it might hit the jacks - nothing. Took off the backplate and the knobs to recreate the working scenario from yesterday - still nothing.

Time to break out the DMM and signal tester. I traced the schematic down and got signal all the way through - until the volume pot. I have no signal coming out of lug two of the pot now, no matter where the knob is set. I reflowed all three solder joints just in case, but no luck. I'm not entirely sure this is the problem. Since I'm not getting signal when the pedal is in bypass either, I checked continuity between my jacks and my switch wiring, and that all checks out fine. If I'm getting continuity between the jacks, how come I'm not getting signal in bypass?

This is pretty frustrating, so I'm hoping one of you fine people can help me sort this. Literally the only things that changed between last night and today are that I put knobs and the backplate on. (I also tightened up the jacks a little, but I'd be pretty surprised if that's causing any trouble.) Photos below. I'm not a good photographer, so there are a few different pictures of the PCB to hopefully try and avoid glare from the camera flash. Thanks in advance, friends!







And a photo I took before this all went down, which shows the topside and wiring:

[mgwhit]

I'd concentrate on fixing bypass before I tried debugging a possibly working board.  Did you test to see if the tip lugs of your jacks were shorting to ground?

[lincolnic]

Matt, you're right - I have continuity between the tip and sleeve of the input jack when the switch is in bypass. Not sure where the short is - I've got electrical tape under the jacks to make sure they're not touching the enclosure when a cable is plugged in, but this definitely gives me something to look for. Thanks.

[lincolnic]

I just poked around for half an hour but can't figure out where the short is. So frustrating! I have to stop looking at this thing for now, or I'm going to throw it across the room. Guess I'll try again tomorrow...

[midwayfair]

(a) Does the bypass work without the power supply plugged in?
(b) It looks like you *could* have nipped the ground wire pressing against the input tip from the circuit board. Try moving it out of the way.

[pryde]

Seems silly but do you have faulty guitar cable? Seams odd you have continuity between input/output in the pedal but no passing of signal when plugged in?

Also, is the pcb resting on the input jack and maybe shorting it there?

[lincolnic]

(a) Does the bypass work without the power supply plugged in?
(b) It looks like you *could* have nipped the ground wire pressing against the input tip from the circuit board. Try moving it out of the way.

Nope, no bypass without power either. As Matt helped me notice, somehow my signal is getting shorted to ground. Can't find where yet, but I'm still looking. I'm not entirely sure what you mean in point B, but my ground wire definitely isn't touching the input tip or the circuit board.

Pryde, the first thing I did was check the cables...they both work on their own. And, as I said in my original post, I tried isolating the PCB with electrical tape where it looked like it might be resting on the jacks, but that didn't solve it.

Keep the suggestions coming, this is all helpful!

[lincolnic]

Well, I'm still not 100% sure what the problem was, but I've got it working now. I think one of the jacks may have been not making proper contact with the enclosure. It's strange - when it was working the first time, the jacks weren't tightened down all the way. After I did, it stopped working; I had to loosen the output jack a tiny bit to get the pedal to work properly.

You know what, though? It sounds so good, it was totally worth the aggravation. Thanks again for all the suggestions, guys.

[pryde]

Glad you got it going. It seams odd that if you loosen the jack (i.e. weaker contact) it starts working? Sounds like it may give you some trouble later at some point. I dunno?

[gtr2]

On the PPP powder coated enclosures you have to sand or dremel away the powdercoat from the inside of the enclosure so the output jack can use the enclosure as ground.  Since you are already boxed you can just connect the sleeve lug to ground on the output jack.  I'd recommend doing this before you use it "live" so you wouldn't have to worry about it again.

Josh

[mgwhit]

Glad you got it working!  I wonder if one of the jacks has an internal flaw that only shorts when you really tighten it.  If it's for personal use, I'd be tempted to leave it as is unless or until the problem turns up again.  Have fun!

[lincolnic]

Yeah, it's just for personal use (and if we're being honest, probably only bedroom use), so I'm going to leave it for the time being. If it starts giving me trouble again, maybe I'll swap out the jacks or rehouse it in a 125B, but for now I'm pretty pleased.