tearjerker wah pot doesnt do anything

[susie_1987]

Hello. I recently completed my tearjerker wah and the pedal does the "wah" but the pot has no effect on the filter freq. The dip switches change the frequency and the trim pots do everything they should. I triplew checked that everything was wired right, reflowed, etc.. The pot is functional, double checked. Maybe it a problem with my inductor? Any help would be appreciated.

wah

14 new photos added to shared album

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[Chuck D. Bones]

I think your inductor is ok.
Are you sure the gear is tight on the pot shaft?
Check the voltage on Q3-E.

 

[susie_1987]

Alright, so I am getting 3.7 volts on the emitter of q2 and 65mv off of q1e. I don't really know what you mean by q3e. Also, the gear is tight, the knob is definitely turning. Thanks Chuck!

 

[Chuck D. Bones]

Q3-E = Q3's emitter. Your readings are good. Let's try this: With power off and nothing plugged into the IN & OUT jacks, measure the resistance from pin 2 of the Wah pot (middle pin) to ground. Rotate the pot to both ends and report the readings at each end. Should be nearly zero Ohms at full CW, and 100K at full CCW.

 

[susie_1987]

The pot goes from 0 to 100. I have pretty much gone through all the basic troubleshooting, so I think the problem might be a little more outfield. Correct me if I'm wrong but doesn't the pot change the current going to a capacitor which changes the center frequency? What would be that capacitor so I can get some readings. Sorry if that wasn't technically correct lol, it's what I sort of remember

 

[susie_1987]

*0 to 100k I meant

 

[Chuck D. Bones]

The two transistors together make a capacitance multiplier. The cap getting multiplied is one or more of the C5 - C13 cap bank. The multiplication factor is governed by the Wah pot. Something in the path from Q1-C thru C4, the Wah pot, C14, Q2 and the caps selected by the DIP switches is either shorted or open, breaking that path. The sound I'm hearing in your video is a fixed wah, so that tells me that the inductor is working and there is probably no signal at Q2-E or one of the larger caps in the capacitor bank is shorted to ground. Visual inspection should uncover something. That DIP switch in the back side might be hiding a short.

Do you have an audio probe?

 

[susie_1987]

Success! I replaced c14 and it works now. Thanks for the insight