Hello Nat,
NH> He gave it to me without a terminator on it. I ran it for those
> 10+ years that way with no problems, as that's the way he
> apparently ran it.
I'm guessing that either a) the external disk was terminated inside
the box somehow or b) it was indeed unterminated, but your grandfather
got lucky in that it did not cause noticable problems.
NH> I moved the drive over to my Classic II.
It's possible that a Mac Plus is more forgiving of incorrect
termination than a Classic II (the newer machine almost certainly
pushes its SCSI bus faster, making timing more critical).
A SCSI bus should be terminated at each physical end (and only there,
ignoring for a moment 16-bit 'wide' SCSI busses that you're not going
to find on a Plus or Classic II). The Mac is at one end of the chain
and terminates that one, so you only have to worry about the other
end. If you can find someone locally who is familiar with SCSI gear,
they should be able to check for you whether the drive is terminated.
At the same time, they can check the SCSI ID: if the Classic II has
an internal hard disk, it's important that your external drive is set
to a different ID. The internal may be set to ID 0, the Mac will use
ID 7 for itself, if you have nothing else attached, there's a good
chance that ID 1-6 are available.
NH> Not owning any documentation on this, I go with the
> distributor's recommendation and pick up an "active" terminator.
> Whatever the hell *THAT* means.
As I understand it, active terminators include a voltage regulator
that uses the termpwr signal from the bus to provide 'better'
termination than old-fassioned passive terminators. The catch is that
not all Macs supply the termpwr that an active terminator needs. Try
an inexpensive passive terminator (which should be adequate for the
kind of SCSI found on compact Macs), but only once you're sure the
drive is not already terminated.
It is also possible that the drive itself has stopped working, which
would be a nice opportunity to upgrade the enclosure with a larger
drive.
I hope that this helps.
- Andy.
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