9203 photocells in a Naughty Fish producing oscillation

[midwayfair]

Here's a weird one. I tried using 9203s and a single LED in the Naughty Fish, and in many settings on the Sweep control I got motorboating oscillation. I measured them in the dark and they're idling at 200K just like they should and with the up/down switch flipped they're idling under 10K.

VTL5C1s work fine on the same PCB with no oscillation and measure the same resistances in-circuit.

Anyone have any ideas? This is a truly weird one.

[drolo]

try to measure the voltage across R22 when you have motorboating to calculate the current drawn. It might be exceeding the Op Amps capacity for some reason.

[midwayfair]

try to measure the voltage across R22 when you have motorboating to calculate the current drawn. It might be exceeding the Op Amps capacity for some reason.

I think if that were true the sweep control would have stopped the motorboating.

But current draw with a single LED (for both photocells) should be less than with two LEDs in series (from two photocells) regardless.

I'm just making excuses to avoid desoldering again, though.

[John S]

Did you ever figure out what was going on with this issue. I'm having the same issue with the photocells

[midwayfair]

Did you ever figure out what was going on with this issue. I'm having the same issue with the photocells

Nope, I just used the 5c1s to stop dealing with it.

[John S]

Cool. Thanks