CDJ 350 Tempo Fader Not Working

Hi,

I searched all over the internet and I haven't yet been able to find the solution so I'm posting here, hoping to get a quick reply.

My friend has CDJ 350s and they used to work as they should. He sold them a few months ago but they came back for some reason - since then, the tempo faders on both CDJs seem to be locked - permanently.

The problem is the following: when you load a track, the pitch changes from 0% to 3.9% in a few seconds (like if I were moving the tempo fader even though it stays on 0% physically). Now, when you try to move the fader, the pitch doesn't change. First I thought that I left the BPM lock on but to my surprise, it was off.

The weird thing is that both CDJs have the same problem, no visible physical damage and they're fairly new. I opened one's case and the electronics seem to be fine.

Any other solution? I'll do the firmware upgrade today but I doubt it'll help.

Thanks in advance,

Matija