In article ,
D Yuniskis wrote:

David Nebenzahl wrote:
So I made up a SCSI cable for the scanner I got off the street

(sigh) SayNoMore. SCSI cables need to have controlled impedances.
Even at ASYNC speeds, you can get all sorts of reflections that
can cause havoc.

Not always. I've seen (and owned) a number of SCSI peripherals hooked to
older Macs with no terminators and no problems. Strings up to three or
four units long, hot switching power to devices as needed, no problems.
Period.

In one case, I had such a setup that worked perfectly for years under OS
9, but failed totally when I migrated to OS X; fixed it by adding a
terminator, but I believe the problem was still software (SCSI timing
was faster with OS X and the lack of terminator became an issue solely
because reflections didn't have time to die out).

I'd guess that if a particular setup works most of the time, the problem
is more likely to be software than hardware. Check for better drivers.

Isaac