Hello,

I only see the electrolitic capacitors on your PCB.
I see none of the 100 nF capacitors ( C2, C4, C5 and C6 ) on your PCB.
They are a must for stability.

Bertus

I'm afraid I left those out... I thought that: since I already had the big ones, why add the small ones; then tried it on a breadboard and it seemed to work well without them.

 

Hello,

Yes, as the stablility can not be garanteed.
Can you measure on the + 12 Volts and - 12 Volts with your scope?
Are the glitches visible on them?

Bertus

 

see if the comparator is switching at the same time.

 

Hello,

Yes, as the stablility can not be garanteed.
Can you measure on the + 12 Volts and - 12 Volts with your scope?
Are the glitches visible on them?

Bertus

I think you got it.

There is a tiny, almost imperceptible ripple on the output of the positive regulator. I superimposed it to the output waveform from the FG, and bingo, it fits like a glove.

You are a star...

 

Hello,

Yes, as the stablility can not be garanteed.
Can you measure on the + 12 Volts and - 12 Volts with your scope?
Are the glitches visible on them?

Bertus

Really? Datasheet attached.

 

Just checked the negative regulator, and there's a different ripple, this one fairly large (80mV p-p) almost in the form of a saw wave at 100Hz. This is what I saw before when I blamed the pot.