The most common mistake is plugging either the disk or display cable onto the main board offset by a row of pins. If you do this with the display cable you will blow three surface mount fuses - but there is no reason to remove this cable to perform a disk upgrade.

You also need to be careful with the VFD - the glass tube is generally very strong, but the fill nipple (near the rotary control) can be easily snapped off if struck.

When removing and refitting the drive mount care has to be taken not to scrape any components on the back of the display board or on the main board.

When fitting a second drive, insulating tape must be fitted to the mounting plate to prevent components on the underside of the drive shorting to the metalwork.

I think that pretty much summarises the common problems. Repair costs vary, but in general labour will be charged at $50 an hour and a new VFD costs around $75.

Rob