> X-Sender: hotzmail@hotzsun.jpl.nasa.gov
> Date: Tue, 10 Mar 1998 12:48:12 -0800
> From: "Henry B. Hotz" <hotz@jpl.nasa.gov>
> Cc: gregdunn@indy.net, port-mac68k@NetBSD.ORG
> Precedence: list
> Delivered-To: port-mac68k@NetBSD.ORG
> 
> At 1:02 AM -0800 3/10/98, cruller@unicom.net wrote:
> >> > The Q800 has an extra scsi plug on the internal cable, 1 for cd, 1for
> >> > 1/2 height rack & 2 for full height rack.  I've got the usr drive on the
> >> > last scsi plug.  I'll try the second to last plug, maybe that will help.
> >> > :-)  Thanks!
> >
> >^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^!THIS WORKED!^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> 
[snip]
> pretty short.  My experience is that you can get things to work by breaking
> the rules sometimes, but if you do then the fix may not hold as humidity,
> age, whatever change.  In this case the rule is: both *ends* of the chain
> must be terminated.
> 
> I have seen internal plug terminaters at Fry's sometimes.  If you are
> running with the last plug empty I would suggest you get one, put it in the
> last plug, and disable termation on the relevant internal drive.
> 
> I know this has been an ongoing thread.  Appologies if I duplicated other
> postings.
> 
> Signature failed Preliminary Design Review.
> Feasibility of a new signature is currently being evaluated.
> h.b.hotz@jpl.nasa.gov, or hbhotz@oxy.edu
> 
> 
> 

There is another podssibility that hasn't been mentioned yet that I
have seen more than once on older equipment....

Bad contacts.

Most connectors are IDC (insulation displacemaent connectors) and get
crimped on to a ribbon cable.  As the ribbon ages it goes a bit harder
and then when you bend and unbend it fitting new drives and moving
stuff around, one or more contacts make poor or nonexistent
connections either all the time or at certain degrees of bend and
stress on the ribbon (i.e. moving the cable, flexing it next to the
connector etc will make it either work or fail).  This can also happen
on new SCSI ribbons that are cheaply made.  THere's a lot of contacts
on a SCSI and just one crucial failure can kill it or corrupt data.

Basically if it works leave it alone.  Playing with connection
positions only helps if it won't work - if a connector on a ribbon
won't work with a drive try a different position on the ribbon and
remember which one didn't work - but only after you have got your
terminations sorted.  And if you are handy buy a new IDC connector and
fit it to the ribbon just where you want it - they aren't very
expensive and with care and a vice (vise) are easy enough to fit.

Russell. 



Russell Gasser
Development Technology Unit (DTU)
Engineering Department
University of Warwick
Coventry CV4-7AL
England

Tel/Voicemail +44 (0) 1203 522339
FAX +44 (0) 1203 418922
E-MAIL  esrpo@eng.warwick.ac.uk

Opinins expressed are personal and not the official position of the
DTU or the University of Warwick.