Mech vario (PZL, I believe) got stuck on 5kts up. When lift exceeds that (e.g. on tow), needle moves up and then back down to 5. Never goes below 5.

Electric vario that is, to my best knowledge, connected to the same TE source behaves normally.

Questions:
- Can something like this be caused by an issue in the tubing, etc. or is it more likely an internal issue with the vario itself?

- Any particular way to tell?

Thanks,
-MB