Macintosh: Multiple SCSI Device Startup Problems



I have a Macintosh IIx with internal HD80 SC drive, AppleCD SC, and Apple
Scanner. When all devices are connected, the last device on the SCSI chain
does not show up.

I have already tried switching the order of devices, changing SCSI ID numbers,
and starting up the three machines in every possible order. The last device is
terminated but I still can't see it. The first device always works (whether
it's the AppleCD SC or the Apple Scanner).

Do you have any suggestions?

You are encountering a problem known as impedance matching. This is a known
problem with the Apple Scanner. The situation occurs when the impedance
created by a combination of devices and terminators on the SCSI chain causes
one device to be "lost" on the chain.

Change the impedance of the SCSI chain by adding one or more terminators, SCSI
devices, and/or additional SCSI extender cable, and the device will reappear.


Published Date: Feb 18, 2012