Surf pi pro unusual behaviour

[Andi68]

What is the function of the SAT cap?

Is he necessary?

[qute1]

thanks kt urastar and carl ualso.

[kt315]

c7

[qute1]

Which is the sat cap carl ?

[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]

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.

[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!

[Koala]

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

[Gwil]

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

Basically, trust nothing.

[qute1]

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

[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]

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.

[dbanner]

I wouldn't go the freeze spray route. This isn't complex mother board of high end device. Just recheck the integrity of the soldering and parts placement, change out some suspicious caps/ components etc.
I'm sure it is easy fix.

[qute1]

thanks guys i am going to have squizz in a bit and will certainly check those caps, have to get some freezex (takes awhile now maplin is gone ebay is the only way now).....will give an update later.

[waltr]

It sounds like a component (or solder joint) is misbehaving as it warms up. I've found faults like that by carefully cooling one suspect at a time using a freezer aerosol and seeing if the symptoms change.

I also thought of a bad solder joint. Could also be a bad cap, there is AC coupling after the threshold adjust stage or socket, etc.

Freeze spray can be helpful to find bad spot. Good luck.