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 Post subject: Wah pedal not working
PostPosted: Wed Mar 21, 2018 11:22 pm 
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I'm new to building pedals (actually new to electronics -- this is my third pedal). The bypass seems to be working, but there's no sound when the wah is activated. Attached are photos of the build. I've already tried resoldering/reflowing many of the joints. Thinking this may be an opportunity to learn to use a multimeter? Any advice appreciated!


Attachments:
File comment: Wiring.
IMG_3435.JPG
IMG_3435.JPG [ 882.93 KiB | Viewed 744 times ]
File comment: PCB bottom
IMG_3433.JPG
IMG_3433.JPG [ 935.96 KiB | Viewed 744 times ]
File comment: PCB top
IMG_3426.JPG
IMG_3426.JPG [ 928.68 KiB | Viewed 744 times ]
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PostPosted: Thu Mar 22, 2018 10:57 am 
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I'd say your soldering is still an issue, particularly on the footswitch. But My main concern is with the pot: can't tell for sure but are the solder lugs pressing against the pot case? If so, lift those (carefully) because they are shorting.


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PostPosted: Thu Mar 22, 2018 12:28 pm 
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Thanks! I just checked, and I don't see the lugs contacting the pot (photo attached). Maybe I should just undo and redo the footswitch soldering (I didn't touch that last night when I went over the PCB).


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IMG_3436a.jpg
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PostPosted: Thu Mar 22, 2018 12:46 pm 
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Great! Just the angle of the photo. Redoing the footswitch might help. Just be careful not to overheat it - sometimes that will melt the plastic and screw things up inside.


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PostPosted: Tue Mar 27, 2018 10:50 am 
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I redid the footswitch, this time the way Stephen on the forum recommended. No change :(
I'm not sure what my next step would be -- there's an open electronics group meet tomorrow, I can take it there and ask if anyone has experience troubleshooting circuits. Aside from that, ???


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IMG_3484 2.JPG
IMG_3484 2.JPG [ 945.04 KiB | Viewed 704 times ]
IMG_3485 2.JPG
IMG_3485 2.JPG [ 872.53 KiB | Viewed 704 times ]
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PostPosted: Tue Mar 27, 2018 12:21 pm 
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Probably the most effective way to troubleshoot this problem would be with a signal tester--you follow the signal path through the circuit (using the schematic for guidance) until you find where it's dropping out. The tester is a very simple device; if you don't want to buy one (either to save $$ or time), it's pretty easy to build one from the BYOC instructions here: http://byocelectronics.com/signaltesterinstructions.pdf

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PostPosted: Sat Apr 07, 2018 10:13 pm 
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I started testing the signal as you suggested. It goes through the first capacitor, the gain trim, and the mids trim. I get a signal at the transistor base but not at the collector or emitter. I replaced both the socket and transistor, and it still gives no signal out. No signal through the bass or Q trims. Nothing at the 22k resistor -- I removed it and tested it, it works so I replaced it.. I do get a signal at the buffer volume and through the IC.

I also tested the stomp switch, I don't have a LED so I'm not sure which is "on" and "off." One way I get signal through the 1, 2, 4 and 6 lugs, and the other way I get signal through the 1, 4, 5 and 6 lugs. (1 is tip in, 2 is PCB in, 3 is Sleeve in, 4 is PCB out, 5 is Tip out, and 6 connects to 1).

Suggestions?

Thanks!


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PostPosted: Mon Apr 09, 2018 4:57 pm 
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What voltages are you getting on the collectors of each transistor?

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PostPosted: Mon Apr 09, 2018 7:31 pm 
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Hmmmm . . . I had been using the signal tester to just follow the audio path. How would I test for voltage on the collectors? Would the pedal be powered or unpowered?


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PostPosted: Mon Apr 09, 2018 8:28 pm 
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Use a multimeter set to read DC voltage; if it's not an auto-ranging meter, set the voltage range to 20V. The black probe goes to ground (a screw boss in the enclosure works well for this) and the red probe to your test point. The collectors of the two transistors are marked in the attached PCB diagram. The pedal needs to be powered when you do this.

Attachment:
wah_tranny_collectors.jpg
wah_tranny_collectors.jpg [ 62.22 KiB | Viewed 589 times ]

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PostPosted: Tue Apr 10, 2018 6:17 pm 
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Zero.


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PostPosted: Tue Apr 10, 2018 7:29 pm 
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Well, that's not good. That was with your power source connected to the pedal and a cable inserted into the input jack?

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PostPosted: Tue Apr 10, 2018 11:09 pm 
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Oh, cable inserted in the input jack! Yeah, that changed the values.

3.94 for the one upper left, and 8.67 for the one on the lower right.

Thanks!


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PostPosted: Wed Apr 11, 2018 10:33 am 
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musicmatters wrote:
I started testing the signal as you suggested. It goes through the first capacitor, the gain trim, and the mids trim. I get a signal at the transistor base but not at the collector or emitter. I replaced both the socket and transistor, and it still gives no signal out. No signal through the bass or Q trims. Nothing at the 22k resistor -- I removed it and tested it, it works so I replaced it.. I do get a signal at the buffer volume and through the IC.

I also tested the stomp switch, I don't have a LED so I'm not sure which is "on" and "off." One way I get signal through the 1, 2, 4 and 6 lugs, and the other way I get signal through the 1, 4, 5 and 6 lugs. (1 is tip in, 2 is PCB in, 3 is Sleeve in, 4 is PCB out, 5 is Tip out, and 6 connects to 1).

Suggestions?

Thanks!



The output buffer is the end of the circuit. If you are indeed getting signal at the center pin of the buffer volume trimmer, but no signal coming out of the out jack, then that would imply that your problem is with your wiring between the circuit board and the out jack.

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PostPosted: Wed Apr 11, 2018 5:51 pm 
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Somewhere between the resoldering and replacing a part or wire or two, the wah now wahs!!!

Now I have to adjust the tone.

Thanks for all your help in troubleshooting this pedal with me!


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PostPosted: Wed Apr 11, 2018 9:21 pm 
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Glad to hear you've got it "wahing!"

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