Arachnid - no dry signal

[joeyd]

I've been trying to troubleshoot this one to no avail. I'm getting a strong dry signal up to R4. At R20 the volume drops. It's faint at the mix pot. After the mix it's gone - no audio (wet or dry) is passing.

I made a questionable choice when I drilled the enclosure, totally forgetting that the shaft on the 1P8T isn't very tall. I wanted side jacks, but they're not low enough to let the board sit nicely with 1P8T protruding enough to be useable. You can see my janky extensions but they don't sound like they're causing issues - I can hear a wet signal with the distinct effects. I had to mutilate the pots a bit to get them to fit (they were PCB-mount pots that got chopped down). I could see that having caused a problem. I pulled the board out of the enclosure just in case something was grounding. This made no difference when I was testing.

I'm currently trying to figure out where to begin replacing components. I reflowed the solder joints on the B10k pot. I replaced R20 (it looks like I need to touch up the solder on one side). I'm going to try a different B10k pot. Any other thoughts? Am I totally missing something that's obvious in the pictures?

There's a bypass signal, the FV-1 has an output signal at Pin28, the ctrl pots seem to be working, the 1P8T seems to be working.

 

[joeyd]

I tried a new pot, no change. Pulled the board out to make sure I wasn't grounding anything off on the case. I'm pretty sure that the issue is somewhere in this section of the schematic:


I tried placing a jumper with a 15k resistor on R4 to see if I could bypass the section and get a dry signal beyond whatever part I janked up (in case I lifted a pad or something) but a) there's still no sound on PIN 1 of the TL074 (I've tried swapping the TL074) and b) I think I'm guessing my way through this hoping for success.

 

[PJS]

With no audio, what voltages do you get at R4/R20 with the mix pot in middle, one end, other end. Same for R19/R21

Do you get the effected audio at IC1.1?

 

[joeyd]

R4/R20: 4.1v
R19/R21: 4.1v
IC1.1: 4.1v

The voltages don't change as I move the mix pot around its range. I also tried a different B10k pot. When I use my audio probe - with the mix turned completely clockwise I can only hear the wet signal on the left side of R19, nothing on R21. With the mix turned all the way down I get a quiet wet signal. With the mix turned all the way up I get a faint dry signal on IC1.1. I'm not really sure how to interpret that - am I measuring incorrectly?

 

[phi1]

You can check the pot by resistance across 1-3 and 1-2 and 2-3 as you put the pot in different positions.

It’s handy that youve already used the audio probe to track down the area. The R20 and R4 solder joints looks a little questionable, and you could see if there’s any short to ground or disconnect with the beep mode on the meter