Capacitor Question (in distortion pedal)

[canman]

Sorry for the delay...here's the picture:



If anyone sees anything that's off, I'm all ears!  And yes, that long 1k resistor isn't connected, as per previous discussion and testing.  Just haven't put it back in yet.  

The solder blob is my way of doing double links.  It's easier to do it this way then it is to cram two wires into one hole...sorry if that's a bad way to do it, haha!

[ggedamed]

IMO, voltages at pins 3 and 5 are off - not enough to be a problem itself, but as a symptom.
I would take out IC1 and C1, C6, C5 (to be able to test the DC condition of IC1A and IC1B in isolation). Then - with IC1 out of the socket - I would test voltages at pins 3 and 5. They should be around 4.5V, the same value as at pins 10 and 12. If that's OK, I would put back IC1 (C1, C6 and C5 still out of the board) and measure again - the voltages should not change significantly. If that's OK, I would put back the capacitors, one by one, measuring each time.
It could be a bad op amp.

[JFace]

It could be a bad op amp.

This is what I think it is. I've had TL074 ICs give me the proper voltages but not perform the way I expected. After swapping it, everything works.

[merlinb]

IMO, voltages at pins 3 and 5 are off - not enough to be a problem itself, but as a symptom.
...If that's OK, I would put back IC1 and measure again - the voltages should not change significantly.

Those voltages are normal. In reality they are close to 4.5V, but the voltmeter pulls them down because it creates a divider with the high-resistance pull up resistor, causing a low reading around 2 to 3V. This always catches people out.

[canman]

I should have more time to debug today, I will resolder that resistor leg and swap out the TL074.  I'm REALLY hoping that's the problem!!  Like I've said, my understanding is limited.  So here's a question...if the opamp really is bad, why would the voltages look OK?  Or are the voltages only external to the opamp, meaning that the opamp doesn't change or modify the voltages at all?  (My guess is the second question is more accurate, which is why my voltages are OK)

And one more question...are there any ways to check if an opamp is bad, other than just replacing it?  Any tell-tale signs that you've got a bad one, aside from things not sounding right? 

[canman]

Update...not a bad opamp.  Switched it out and still not fixed.  Is it still worth pulling out C1, 5, and 6 and testing the voltages at the socket, since I think I can safely say it's not a bad opamp?  (Unless of course, I got two bad ones.  Highly unlikely)

[ggedamed]

IMO, voltages at pins 3 and 5 are off - not enough to be a problem itself, but as a symptom.
...If that's OK, I would put back IC1 and measure again - the voltages should not change significantly.

Those voltages are normal. In reality they are close to 4.5V, but the voltmeter pulls them down because it creates a divider with the high-resistance pull up resistor, causing a low reading around 2 to 3V. This always catches people out.

D'OH! It surely caught me. For the other noobs like me, here's a drawing showing what's hapenning when you connect a normal 1M input resistance DMM to a op amp bias point:

See how DMM-R creates a voltage divider with R3? And it's worse with 1M or bigger bias resistors.

Update...not a bad opamp.  Switched it out and still not fixed.  Is it still worth pulling out C1, 5, and 6 and testing the voltages at the socket, since I think I can safely say it's not a bad opamp?  (Unless of course, I got two bad ones.  Highly unlikely)

No, it isn't. Your voltages are good. It could be worth to try a different capacitor instead of C5 - different value and construction. I once had problems with a whole batch of 680n capacitors and it took me 6 or 7 capacitors to convince me about that.