Kapffer@UAIMZA.MATHEMATIK.UNI-MAINZ.DE (01/25/91)
I'm stuck with the following problem:
A friend has assembled a hard disk based on a Quantum 80 Meg 5.25" SCSI
drive, including the soldering of an appropriate cable between the drive
and an Apple SCSI card. The setup works fine when connected to an Rev C
(non-DMA) SCSI card, but fails with the newer DMA card.
The only notable reaction of the drive is when the DMA SCSI card gets
initialized (while booting ProDOS 8 or GS/OS); it goes through the same
head calibration sequence which can be heared after turning on the drive.
None of the supplied utilities (nor ProDOS 8 itself) can see any device on
the bus (the drive is the only one connected).
I've tried to change any parameter I could think of (and easily carry out),
but nothing made a difference: Turning of DMA, changing the SCSI ID of the
drive, removing and re-installing the termination resistors on the drive.
The SCSI DMA card itself works fine with a Rodime drive (as does the Rev C
card); it's also _no_ DMA problem - the RAM card is a fully populated Apple
card (and, as already said, turning of the DMA option didn't change
anything).
I'm beginning to suspect that it could be a problem of missing termination
power (there's also a troubleshooting entry in the manual pointing in this
direction).
So, my specific questions are: What are the differences between the Rev C
and the DMA card (as seen from the hardware interface) which can make a
drive fail as described - is there a difference in the way termination
power is supplied ? (I always thought the Rev C card doesn't supply the
power either.) If it is the problem, what would could be done to fix it ?
Can anobody think of another reason ?
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M a t t h i a s K a p f f e r
email: Kapffer@uaimza.Mathematik.Uni-Mainz.DEericmcg@pnet91.cts.com (Eric Mcgillicuddy) (01/26/91)
>A friend has assembled a hard disk based on a Quantum 80 Meg 5.25" SCSI >drive, including the soldering of an appropriate cable between the drive >and an Apple SCSI card. The setup works fine when connected to an Rev C >(non-DMA) SCSI card, but fails with the newer DMA card. Was this formerly an internal drive that had a power supply and case added on? The DMA SCSI card terminates its end of the chain, does your hard drive terminate its end? Signal reflections from the unterminated end can easily screw up the communications signals. UUCP: bkj386!pnet91!ericmcg INET: ericmcg@pnet91.cts.com