Revox B970 malfunction

Hi everybody (it's B790 the correct name)

First issue:
Has anyone of you Revox owners happen to experience this:
less than half a minute after pushing Play, the playback stops and the moving headshell from the arm zeroes back to 00.00. You push play again, in 20 secs it happens again.

Second thing:

Can please someone direct me to where I can find instructions to remove the cartridge from the tonearm or from the shell, it’s a Shure V15 that I need to relocate, since the repair of the turntable in Romania seems not very likely...

Thank you kindly for reading this!