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From: barry@primerd.prime.com
Newsgroups: comp.sys.mac.hardware
Subject: Removing Internal SCSI Termination
Message-ID: <226700004@primerd>
Date: 12 Mar 90 22:34:00 GMT
Lines: 36
Nf-ID: #N:primerd:226700004:000:1747
Nf-From: primerd.prime.com!barry    Mar 12 17:34:00 1990


There have been a few queries lately about removing internal termination
from a SCSI device.  The reason one would want to do this is that the
first and last device in SCSI chain must be terminated.  An internally
terminated device _must_ be at the end of the chain, which limits where
it can be used in a chain of more than one device.  Switching to the use
of an external terminator adds configuration flexibility at the cost of
the external terminator (about $30). 

Generic instructions:

An internal terminator is a set of three resistors that should be near
the internal 50-pin SCSI connector on the device.  This is not to be
confused with the 50-pin connector on the outside of the case containing
the device.  The internal connector on the device will have flat 50-pin
cable connecting it to the back of the external connector on the case.

Some devices have a jumper that controls whether or not the terminator
is power - you can remove termination on these devices by removing the
jumper ...  if you have a manual that identifies the jumpers.  You can
_always_ remove the internal termination by removing the three resistors
- these are likely to be a BLUE ceramic package with 8 pins.  You have
to remove all three of the resistors (with the device unplugged, of
course). 

When in doubt, leave it alone and seek an expert. 

Hope this helps,
			Barry

------------------------------------------------------------------------
Barry Wolman                      | barry@s66.prime.com
Principal Technical Consultant    | 500 Old Connecticut Path
Prime Computer                    | Framingham, MA 01701
                                  | 508/879-2960, ext. 4187
------------------------------------------------------------------------