SCSI Voodoo

The SCSI chain is the most common source of crashes and hangs. Once you have established that the machine is getting power, unplug the entire SCSI chain and try to restart. If the machine works without any SCSI devices, start adding them to the chain one by one to isolate the problem.

NEVER plug in or unplug a SCSI device while it or the computer are turned on.

To work properly, the SCSI chain must be:

Uninterrupted - A partially plugged in device is lethal. Properly terminated - A terminator must be on each end of the chain, and there must be termination power available at the end of the chain. Less than 27 feet long - Actually a more reasonable limit is about 15 feet. Properly addressed - Every device on the chain must have its own number. The CPU is normally device 7, and the internal drive is normally set to device number 0. Apple internal CD ROMs are normally set to ID 3 (Power Computing uses 2 or 3)