Classic mac fun (and some questions)

Curtis H. Wilbar Jr. rescue at
Fri Jul 10 06:27:47 CDT 2009

Teo Zenios wrote:
> ----- Original Message ----- From: <trag at>
> To: <undisclosed-recipients:>
> Sent: Thursday, July 09, 2009 4:05 PM
> Subject: Re: Classic mac fun (and some questions)
>>     (continued...again...)
>> From: "Jeff Walther" <trag at>
>> To: cctech at
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>>> Date: Thu, 9 Jul 2009 12:00:48 -0400
>>> From: Ethan Dicks <ethan.dicks at>
>>> I tried to look that up and found it easy to see that the IIfx needed
>>> something odd (I couldn't find specifics), so well done there.  It
>>> would be interesting to get the details to see where Apple went off
>>> the rails from the SCSI spec.
>> IIRC, it's a matter of adding a capacitor and maybe a resistor to a
>> regular terminator.  There's an Apple Technical Note or similar 
>> available
>> somewhere.  I probably have a copy squirreled away on my hard drive at
>> home.   And I think I remember that they use a somewhat higher value
>> capacitor (so add a smaller one in parallel on an existing 
>> terminator) and
>> a lower resistance (so again, add a resistor in parallel).   But I could
>> be misremembering.
>> Again, IIRC, the IIfx's SCSI was too noise sensitive.  But I've also
>> heard/read that that was only true for the early production run and that
>> the later built machines did not need the funny terminator.
> Neither of my IIfx systems need that terminator to work.

I wonder if using an active terminator would work as a substitute for the
special Apple terminator ?

Anyone know a way to check a terminator to see if it is the special one ?  I
have one black one that was given to me as a believed IIfx terminator, 
but it is
not an Apple one.... so I don't want to trust what it is merely because 
it is black.

Anyone know how to ID which IIfx systems need the black one, and which 
ones are
of later rev that don't need it ?

-- Curt

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