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From: gareth@vcn.bc.ca (Gareth Jones)
Newsgroups: comp.sys.apple2
Subject: Re: Zip drive not working with High-Speed SCSI. Help!
Date: 20 Feb 1997 16:20:31 GMT
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ToasterKing (toastjuice@aol.com) wrote:
: hard drive to the end of the SCSI chain. I've heard there is a simple
: modification I can do to my HS SCSI card to make it supply termination
: power. It requires soldering a jumper wire from a +5V source on the card
: (or anywhere in the GS, for that matter) to one of the SCSI pins. If
: anyone has seen this mod or could tell me which SCSI pin to solder the
: jumper to, I'd appreciate it if you'd let me know.
:
:
: Thanks!!
:
You can find the picture of the mod on http://ground.isca.uiowa.edu/apple2
somewhere (in the documentation folder, I believe). It has a name
something like HS.SCSI.GIF, although that may not be exactly right. The
following article from _Apples B.C. News_ will supplement, not replace,
the GIF.
-Gareth
Apple II Caf� (October 96): Modifying Your Apple II High Speed SCSI Card
to Supply Termination Power.
Al Crout
For a SCSI system to work properly, termination power must be
supplied by one device in the SCSI chain. With a minor modification, the
Apple II High Speed SCSI card can be adapted to supply termination power.
Supposing you have just purchased a new, larger (bigger, better,
faster) hard drive thinking: "At last, I can get rid of all these small
drives I have accumulated!". However, after a few hours of preparation,
you discover that your new hard drive is not recognized by system software
unless...one of your old drives is part of the SCSI chain. AAARRGH!
According the the High Speed SCSI Card Owners Guide, the problem
is:"A drive won't work by itself but it will work when connected to
another drive" and the solution is: "The hard drive may not supply
termination power, in which case it can never be used alone...". Well, the
manual fails to mention that the High Speed SCSI card is itself a SCSI
device and it, too, fails to supply termination power. You can easily
verify the problem by connecting your new drive to a friend's Sequential
Systems RAMfast SCSI card, which does supply termination power, and
observing how well your new drive works on its own.
Modifying the Apple II card is easy and inexpensive. In fact, a
diagram of the mod was recently circulating in one of the Apple II
internet newsgroups and should be easily obtained (it's also available
from our IIGS disk library).
After carefully removing the SCSI card from your Apple II and
familiarizing yourself with the diagram and the main components of the
SCSI card, all that is necessary is to obtain a 1N914 diode (readily
available from an electronic parts store), clip its leads and solder it to
two points on the back of the High Speed SCSI card while observing the
normal precautions when dealing with heat-sensitive components like
diodes, IC's and fingers.
Re-inserting your High Speed SCSI card and reassembling your SCSI
system should give you the desired results: your new hard drive should now
be recognized on its own by the system software.
By the way, you may find a gizmo called the "SCSI Sniffer" helpful in
diagnosing SCSI problems. The SCSI Sniffer attaches to the end of the SCSI
chain, providing termination. The feature that sets it apart from other
terminators is the addition of seven LEDs (Light Emitting Diodes) which
indicate various SCSI activities including, termination power, I/O, ACK,
REQ, etc. The MAC Station, in Maple Ridge, sells this item at a discounted
price.