Surf pi pro unusual behaviour

[qute1]

Excellent i have lots of tl072 and i am not sure my lm358 are genuine they look suspiciously like some others that have been posted here as fakes.

[Carl-NC]

Most likely something at or past the SAT cap.

1. SAT cap is leaking badly; if you short across the gain pot and the problem mostly goes away, this is it.
2. LM358 is drifting; should be worse at high gain, much better at low gain.
3. A component in the Threshold adjust is drifting badly
4. D3 or 22k is drifting badly
5. The speaker driver (MPSA13) is drifting badly
6. The speaker is bad

[qute1]

Thanks car i will check them i am running out of things to swap out

[Gwil]

Less likely perhaps, but the timing of the sample pulse(s) could be drifting. Just a thought.

Basically, trust nothing.

[Koala]

If you warm it up slightly with a hairdryer does it start to drift quicker?

[qute1]

Cured drifting i think (swopped lm358p for lm358m smd on a converter board) just got to get it back in range now! just off to try 50k delay pot as much more sensitive to slow coil naughtiness now!

[qute1]

Nope that didn't work just get nurrrrrr all the way through now no lock anywhere and its kicking the coil fine etc just can't seem to figure it out, i can trim to ovolt on pin 6 r10 pot and can adjust r2 to match but no lock even tried 100k delay pot nothing nada just nurrrrrr starting to do me nut in even tried 379uh coil zip nurrrrrr.

[Carl-NC]

Remove the SAT cap. If the problem goes away, it is something before the SAT cap, or the SAT cap itself. If the problem remains, it is after the SAT cap.

[qute1]

Which is the sat cap carl ?

[kt315]

c7

[qute1]

thanks kt urastar and carl ualso.

[Andi68]

What is the function of the SAT cap?

Is he necessary?

[qute1]

Appears to be some sort of feedthrough cap connecting one amp of 5534 to the other i will update when i have had a chance to fondle it.

[kt315]

What is the function of the SAT cap?

Is he necessary?

it 'adds' a property of non-motion/static diagram to motion diagram.

[qute1]

Sorted thanks again guys once i removed and replaced c7 and no joy i tried shorting across gain sens pot and there it was a second crap pot in this kit replaced with a nice quality one and she is running bootiful very good on airtest anyhow gets a thin gold ring at 7" solidly on low delay.
Again thanks to you all, KT315 and carl-nc especially, sometimes you just can't see the wood for the trees and it takes some experienced advice to know just where to chop.......