> I am having trouble with one SCSI tape drive.  No idea why.  [...]

> The tape PowerMacinstosh 6500/300 has the classic Mac 25 pin SCSI.

I have a Power Macintosh 4400 with 25-pin SCSI.  I once opened it up
and was somewhat astonished to see that internally it's a normal 50-pin
Berg, but they simply drop half the lines (grounds) for the 25-pin
connector.  If your cabling doesn't do grounding very carefully, you
may be suffering from unfortunate transmission-line effects (which can
look a lot like termination problems).  SCSI really really likes to
have signal and ground _pairs_; I've never understood why Apple felt it
worth the dollar or two difference to cut corners on the ground pins.

> It strikes me that the behavior is similar to other times I've had
> termination problems, but as far as I can tell the SCSI bus is
> correctly terminated.  Would I have better luck if it were not?

Maybe.  I am not a high-frequency transmission-line engineer; what
little I know of the field indicates that in situations like these it
borders on black magic.

> Should I just pack it in and forego any attempt to use the tape drive
> as part of this set up.

If you aren't afraid to get your hands dirty, you might open up your
machine and see if yours too has 50-pin ribbon cable internally; if so,
you might remove the cable and the DB-25 and run ribbon cable out to
the external devices.  You'd at least get all the ground pins
connected.  If I had SCSI problems on my 4400 (which I don't; I'm not
using SCSI on it), that's one of the things I'd try.

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