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From: Kapffer@UAIMZA.MATHEMATIK.UNI-MAINZ.DE
Newsgroups: comp.sys.apple2
Subject: Apple DMA SCSI & Quantum HD: HELP !
Message-ID: <9101242221.AA00311@UAIMZA.Mathematik.Uni-Mainz.DE>
Date: 24 Jan 91 22:21:21 GMT
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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.DE