Subject: Re: scsi question with sparcstation.
To: Brett Lymn <blymn@baesystems.com.au>
From: Christian Smith <csmith@thewrongchristian.org.uk>
List: port-sparc
Date: 06/23/2006 11:09:20
Brett Lymn uttered:

> On Tue, Jun 20, 2006 at 05:07:35PM +0100, Christian Smith wrote:
>>
>> Except I've experienced a SS20 that had to have the main board replaced
>> due to an unterminated bus. The unterminated SCSI signals caused some
>> hardware failure, though I'm not sure of the details.
>>
>
> Ummm I find that diagnosis _extremely_ unlikely.  The scsi bus is,
> technically, an open collector bus.  If it is unterminated then there
> is supposed to be no voltages on it - this does not preclude the bus
> voltages just floating about and happening to make things work.  The
> "old" style terminators were just a resistor network that held each of
> the bus lines at the right voltage, the scsi devices would then sink
> current to pull the line down.  Modern terminators use an active
> device to do the same thing in a more precise manner.
>
> An open scsi bus would not fail, it may or may not work with devices
> on it but it should be perfectly safe, from an electrical point of
> view, to leave it unterminated.  I suspect something else caused your
> failure.


It was explained to me that the resulting RF from the antenna^Wscsi cable 
borked the main board. I was only young at the time, and didn't a) 
understand and b) care enough to get more details. But I think it was more 
than the SCSI bus and controller that was damaged.

It could of course just been some wacky engineer from Sun putting one over 
us to force us to replace the mainboard. We didn't care, because it was 
Reuters' machine anyway.

Christian


--
     /"\
     \ /    ASCII RIBBON CAMPAIGN - AGAINST HTML MAIL
      X                           - AGAINST MS ATTACHMENTS
     / \