Thumb Sucker - What Did I “FRY”?!?

Caldo71

Caldo71

Active member
Hey folks,

So I had a Thumb Sucker build that was complete and sounded perfect, but THEN…

I started desoldering/resoldering pots and jacks because I wanted to reposotion them…now the ratio control is non-functional…possibly from overheating components in the chain whilst desoldering, otherwise I have no clue why.

What happens now is that for the first (roughly) one-eighth of a turn, the A1M pot passes clear, un-compressed audio, and then all of a sudden and for the remainder of the pot’s full rotation range, it gives me this uniformly dull (like rolled off) and low-volume guitar tone that isn’t really compressed…just shitty.

Before you even ask: YES, I swapped out a brand-new A1M as the very first attempt to fix the issue…NOT the culprit.

So, I was wondering if—to any of the more seasoned people on this board—those “symptoms” might suggest and specific components that I may have damaged?

Just grasping at straws here…thanks!
 
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The first rule of troubleshooting; you don’t talk ab………wait, that’s not it. Oh right, the first rule of troubleshooting is post good clear pics front and back please.
 
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Diynot said:
The first rule of troubleshooting; you don’t talk ab………wait, that’s not it. Oh right, the first rule of troubleshooting is post good clear pics front and back please.
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But I’m lying here in bed, lazy AF, and the pedal is an entire room away. Suggestions?

Kidding I’ll snap some pics in a few minutes but I can pretty much guarantee you won’t see any external damage or shitty solder joints.
 
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Looking at the schematic, the ratio knob is tied to IC1. have you tried swapping that TL072? You may want to go ahead and get the IC voltages while you’re at it. Also maybe make sure with your DMM that the A1M is following a logarithmic sweep (as best you can tell) and not getting janky somewhere mid turn. Also might want to audio probe between IC1 and pin 3 (input signal) and pin 5 (output signal) of the Lm13700, or in the interest of least amount of work possible, have you swapped the lm13700?
 
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Diynot said:
have you tried swapping that TL072?
Click to expand...

Diynot said:
have you swapped the lm13700?
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Hey @Diynot so I was actually thinking about trying a swap out BOTH of those ICs as well as the resistor, but somehow (no idea the culprit even now) I got the problem to go away:

I was about to address your original request to take some pics, and I just got a little obsessive as I was observing how my potentiometer/switch leads were coming off the pads…which actually were keeping me from getting good photos because of their placement. So I took out all the ICs etc did a little more desoldering and re-positioning, plus I took out an the 3906’s IC socket that looked a little funny to me while I was at it. Then I re-cleaned the flux off it all super thoroughly.

Anyhow NOW IT MAGICALLY WORKS AGAIN but I have no idea which of the above was the magic bullet. If I were to GUESS, my money would go on the 3906 socket or it’s seating.

Anyhow, yay!
 
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The braided wires are a new level of spicy for these parts, very nice! There should be an option under the more drop down I believe. Not a flex, but I haven’t had to open a troubleshooting thread in awhile so not 100%
 
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