Phase reversal?

[liquibyte]

I've got a bit of a problem with this circuit and I'm not sure why it's happening.  Sometimes when I power this up the voltage on the negative rail won't get above around 1.5V or so.  If I turn it off and let the caps drain out and then turn it back on, everything is right with the world again and I can get my -18V.  I've been hooked up to the scope (analog) on the output when this happens and it seems to be oscillating wildly but I can't figure out why it's happening and how to fix it.  When things are working, they're working well with a nice waveform on the output.  Am I running into phase reversal here or something else?

[dmills]

I am suspicious about the startup behaviour of U2 (also potentially U1 for the same reason).

In particular ask yourself what happens if U2 output momentarily swings above ground during startup (Which it can do due to the way it is powered), the dynamics are complicated, but I think see a possible instability or latch up.

Try making the positive supply of U2 ground instead of +3V (And the negative supply of U1 ground instead of -3V).

I think there are some words of wisdom in AOE (Second Ed) about this sort of self biasing arrangement and its lockup states.

Regards, Dan.

[alsetalokin4017]

How about more decoupling on the power supply leads to the OP-07s? 100 nf right at the chips.....  ?

[liquibyte]

Well folks, I screwed up.  I should have run a final check of the boards because the zener regulator going to the negative rails op amps didn't have the trace connected to the resistor.  This is a lesson that I won't soon forget.  Double, triple, quadruple check your boards before having them manufactured.  I feel like such a dumbass now.

[dmills]

Learn from it, and get ERC/DRC religion.
The software should catch this stuff when you run the automated checks.

Regards, Dan.