Upper decker debugging [Resolved]

[elenore19]

Apparent fix: Replaced gain pot and C4 capacitor and fired it  back up and it seems to be working.

Original post:
Hey all-  I attached the PDF of the project.
Built up this board today and working on getting the distortion side up and running. Haven't tested the boost yet, but figured I'd fix this one first cause the boost is a much simpler circuit.
Issue: The tone is REAL farty/fuzzy. No sustain at all. Have to hit the strings pretty hard to get sound through. All the knobs seem to be doing more or less what they're meant to do.
I'm thinking the problem is somewhere to do with IC1. I checked the capacitor values surrounding it along with the resistors.

I'm new to using an audio probe, but here's what I found with that.
With IC1, the farty sound seems to be there on both pin 6 and 7 with pin 6 a lot lower in volume.  pin 7 seems to be normal volume but has the farty/no sustain thing going on and only registers if I really hit the strings hard.

I figured maybe there could be a problem with the power getting to the IC1 so I checked R3, R24, R25, R26 thinking that they could be causing the wrong voltage. I also thought it could be a bad chip but I swapped out 2 other chips and had the exact same sound effect happening as before.

Voltages:
IC1
1 - 4.39V      5 - 4.25V
2 - 4.39V      6 - 3.96V steadily drops down to 2.42V over about 12 seconds, this happens every time I retouch the voltmeter probe to it.
3 - 4.20V      7 -  1.343V
4 - 1.5mV     8 -  8.71V

IC2
1 - 3.86V     5 - 4.35V
2 - 3.91V     6 - 4.35V
3 - 3.91V     7 - 4.35V
4 - 0.5mV    8 - 8.72V

IC3
1 - 4.39V         5 - 4.35V 
2 - 3.86V         6 - 4.35V
3 - 3.86V         7 - 4.3V
4 - 1.5mV        8 - 8.72V

I'll keep messing around tonight but I'm burnt out for now. Thanks in advance for any help. Greatly appreciated.

-Elliot

[jimilee]

I haven't looked, but is the boost separated from the drive side? The original wasn't, so you had to have both sides built and connected for it to work. I know my board, they're separate.


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[elenore19]

I haven't looked, but is the boost separated from the drive side? The original wasn't, so you had to have both sides built and connected for it to work. I know my board, they're separate.


Sent from my iPhone using Tapatalk

I could be misreading the schematic. But based on the schematic and a wiring diagram of the pedal they seem to be separated in this version. That's interesting though. I'll try that later tonight just in case. Thank you!

[madbean]

Could be C4 or the Gain pot itself causing the issue. Or, perhaps a small copper bridge on the PCB side. Try removing IC1 and measuring the voltage on pins 6 and 7 with no IC. You should have none. Definitely with the IC the problem seems to be pin 6 and 7 voltages.

You can also use an Xacto knife to gently score around the pads on 6 and 7 to make sure there are no bridges (I'm assuming you've etched a PCB here).

[elenore19]

Could be C4 or the Gain pot itself causing the issue. Or, perhaps a small copper bridge on the PCB side. Try removing IC1 and measuring the voltage on pins 6 and 7 with no IC. You should have none. Definitely with the IC the problem seems to be pin 6 and 7 voltages.

You can also use an Xacto knife to gently score around the pads on 6 and 7 to make sure there are no bridges (I'm assuming you've etched a PCB here).

Thank you for your help!
Definitely still getting some voltage on 6 & 7 without the IC in. I don't have an exacto knife, but it looks clean (i attached a picture). It was an etched board from Keefe here on the forum, looked flawlessly done.
Is there a way to test the capacitor without just throwing a new one in there to see if it works?

I'm gonna replace the pot and see if that fixes the issue, then if it doesn't, I'll try replacing the capacitor.

Thanks again for the help

-Elliot

Not sure how to embed images but here are a couple pictures of the board-

https://ibb.co/Bctrs5J
https://ibb.co/kHJCCny

[elenore19]

Okay I replaced the pot and the capacitor. Still getting some voltages on pin 6 and 7 without an IC in there. So lost on what to do now

[Haberdasher]

I suspect you might have a little solder bridge somewhere.  I can see tiny pieces of solder splattered around on the copper side.  I'd reflow those joints and try to clean those little flecks up anywhere you see them.

[elenore19]

Thanks for the help!
I think the little pieces of solder you see in the picture might be light reflecting off of flux, but I'll double check and clean it up.

I threw a chip in there and plugged my guitar in just to hear it not work one more time and it works now!

I now have steady voltage at pins 6 and 7. So I'm guessing it was the pot? Anyways. This thing rips hard and I'm pumped I got it working. Fingers crossed to the boost side working

Thanks again to everyone for your help-
Should I delete this thread?

-Elliot

[madbean]

No, we don't delete tech help threads. It may come in useful to someone else at some point.

Glad you got it worked out.