Surf pi pro unusual behaviour

[qute1]

hey guys yes i know i am hardly a noob with pi's but i have an interesting one for you bought one of these ages ago https://www.ebay.co.uk/itm/SM-PRO-PI...ector+kit.TRS0 built it found it ok working but a bit snarky moved on to another project.
So anyhow i fired it up today cos can't let a thing like that gather dust thing is it works but the longer it is on the more the threshhold wanders until eventually it wont lock in range at all i have swapped out lm5534 and lm358 and the 7066 for new (not because hot or anything just because seemed a good enough place to start) and still it continues the mosfet is only just warm and no other components are getting hot so any ideas or experiences of similar chaps?

[qute1]

whoops 4066 i meant sorry guys

[Andi68]

Otherwise he works as he should?

What do you have for a voltage source?

[dbanner]

Please explain a bit more. Are you loosing your threshold? Are you not able to get a threshold? Are you not able to maintain a threshold?
Check out the battery voltage when circuit experiences problem. Could be low voltage issue.

[qute1]

yep works fine usual 12v battery pack and everything it just wanders after turn on tune in and i cant figure why i have swopped out the usual culprits to no avail has recomended 270uh coil and although it has been hot here i don't think its thermal runaway just wondered if you guys had any similar experiences?

[dbanner]

yep works fine usual 12v battery pack and everything it just wanders after turn on tune in and i cant figure why i have swopped out the usual culprits to no avail has recomended 270uh coil and although it has been hot here i don't think its thermal runaway just wondered if you guys had any similar experiences?

Wanders after how long? And by how much?
A small amount of deviation from original setting is normal I would've thought. But if it's big drift and it happens in relatively small time, then this is not good.
In other words, if it cannot maintain a stable threshold, and you constantly having to adjust, then there's something wrong with the circuit.

[qute1]

Exactly the purpose of my question, yes it wanders a lot and over the space of a minute or so, so yes there is something wrong i just need some suggestions as to what it might be.

[Andi68]

Bad pots can be the cause, or if you test in the house,
Metal can be a source of interference - pipes, etc

[qute1]

Thanks andi i do test in the house but this effect doesn't occur with any of my other many pi's i might swap the pots out next then i did have a problem with one in that kit anyhow but thought i had sorted it maybe not.

[Andi68]

Remote diagnosis is difficult, maybe someone else has an idea

[qute1]

Thanks for you help andi i will be having a look in a bit but kind of run out of actives to check so may indeed be a passive issue (digs out ancient megger teehee (only joking)) !

[Gwil]

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.

[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.

[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.

[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.