Xref: utzoo comp.sys.mac.hardware:3824 comp.periphs.scsi:618
Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!snorkelwacker!apple!coherent!dplatt
From: dplatt@coherent.com (Dave Platt)
Newsgroups: comp.sys.mac.hardware,comp.periphs.scsi
Subject: Re: Why can't I turn off my tape drive?
Message-ID: <59970@coherent.coherent.com>
Date: 8 Jun 90 20:48:44 GMT
References: <10567@spool.cs.wisc.edu> <1990Jun8.150226.22946@Neon.Stanford.EDU>
Reply-To: dplatt@coherent.com (Dave Platt)
Followup-To: comp.sys.mac.hardware
Organization: Coherent Thought Inc., Palo Alto CA
Lines: 34

In article <1990Jun8.150226.22946@Neon.Stanford.EDU> kaufman@Neon.Stanford.EDU (Marc T. Kaufman) writes:

> Au contraire.  It is definitely a SCSI termination problem.  SCSI terminators
> require power.  Generally, with internal termination, that power is provided
> by the device (and only a very few devices will also allow the ternimators
> to be powered from the bus).

The Teac is one of these devices... its internal terminators will accept
power from the bus if the Teac is powered off.  It's a good design
(diode and fuse to +5, provides power to the bus, will accept power from
the bus, and if you manage to short pin 25 to ground you'll blow the
fuse but won't lose power to the internal terminators as long as the
device is powered up).  I wish all SCSI implementors used circuitry of
this sort.

It's entirely possible to boot a Mac and use the SCSI bus if you have a
powered-down Teac N50 attached to the bus, as long as you're using the
Teac's internal terminators and have some other device (such as the Mac)
providing power to the bus.  Trust me... I do it all the time.

> The answer is to remove the internal termination from the Teac, and add an
> external terminator (which will take power from the Mac II).

I really doubt that this will make a difference.  I'm using a hardware
setup almost identical to Tony's, and its terminators are perfectly
happy.



-- 
Dave Platt                                             VOICE: (415) 493-8805
  UUCP: ...!{ames,apple,uunet}!coherent!dplatt   DOMAIN: dplatt@coherent.com
  INTERNET:       coherent!dplatt@ames.arpa,  ...@uunet.uu.net 
  USNAIL: Coherent Thought Inc.  3350 West Bayshore #205  Palo Alto CA 94303