Sharkfin: LFO doesn't O

[durian]

While the envelope-follower part of the sharkfin works, I'm having problems with the FSH section. In particular, my low frequency oscillator isn't oscillating. Or at least the LED isn't switching on/off. That's driven from the LFO, correct?

I've verified my resistors and swapped out IC4, IC5 and Q4, but the behavior didn't change.

Here are voltages on the IC4/IC5 pins:
IC4:
    1    -8.75
    2    0.003
    3    0
    4    -8.76
    5    -8.75
    6    0.073
    7    9.12
    8    0

IC5:
    1    -5.655
    2    -5.655
    3    0.017
    4    -8.76
    5    -8.08
    6    7.95
    7    9.12
    8    0.005

Can someone provide some reference voltages for me, or even better, suggest a possible failure reason.

Thanks,
mike

[durian]

Well, I found one problem. I didn't check the resistor multipliers well enough. R30, which is 47k, was 47R. This brings my non-inverting IC5 input (pin 3) up to 5.433V. Still no oscillation, though.

The resistor mix-up is sort of interesting, as I've never purchased any 47 ohm resistors. Yes, after checking my bin, I have 25 of them, including the one I mistakenly used. I also have a Digikey part label in my box saying I ordered 25 47k resistors from them. Looks like they made a picking error. I've never had a problem with Digikey before (and I've orders lots of components from them for both my job and pedal stuff), but I think I'm going to start spot-checking my receivables.

I still have some error with my circuit and if anyone has reference voltages, I'd be very grateful.

Thanks,
mike

[durian]

Problem resolved. When I originally placed the op amps, I didn't have any sockets, so I soldered straight to the board. When I replaced IC4 and IC5 I did so without desoldering the pots first. It was an awkward angle to work at and I left a very tiny bridge between pins 1 and 2 of IC5. Since the inverting input, pin 2, was held low, the voltage would never rise as the capacitor (C10) charged (and the capacitor never was able to charge because pin 2 was low) and thus the op amp output never switched from one voltage rail to the other.

Lessons learned:
1) Digikey is not infallible
2) Don't try to cut corners and solder under other components - a couple minutes to desolder and later resolder the blocking component is less than the debugging time when you end up doing a half-assed job

mike

[jimilee]

Thats whatever you just said for you!   

[durian]

Yeah, no kidding. I hope I didn't waste anyone's time. With a bit of luck, this thread will appear when someone else has a similar problem and will give them some insight.

mike