M4data model 9914 tape drive

[shadoooo]

Hello,
I'm repairing an M4data 9914 tape drive.
After fixing some problem with psu, replacing the roller rubber with a cut
of tubing, cleaning mechanical parts, oiling some pulleys, now it starts up
on power on, runs diagnostics, but unfortunately ends with a **BIFF error
(scsi interface).
The drive hasn't been connected to a pc via scsi yet.

I have a couple of questions:
- what should be the correct external diameter of the rubber roller?
- where could I find schematics?

thanks
Andrea