S100 Buss extender boards

Randy McLaughlin cctalk at randy482.com
Sun Jun 5 15:36:36 CDT 2005

From: "Randy McLaughlin" <cctalk at randy482.com>
Sent: Sunday, June 05, 2005 3:06 PM

> From: "Richard A. Cini" <rcini at optonline.net>
> Sent: Sunday, June 05, 2005 2:46 PM
>> All:
>> Part of the goodies that came with my IMSAI was a buss extender
>> board which has a logic probe on it, which I definitely use for
>> troubleshooting this stuck bit problem. One of the transistors on the 
>> board
>> has a lead that's broken at the case.
>> The designation on the transistor is "F444". There's a second
>> transistor marked "F137" which also seems to have shakey leads.  The 
>> board
>> is manufactured by Mullen Computer Boards, model TB-1.
>> Can anyone cross these numbers to a current replacement? Googling
>> has come up with a possibility for the F444 but nothing for the F137.
>> Thanks.
>> Rich
>> Rich Cini
>> Collector of classic computers
>> Build Master for the Altair32 Emulation Project
>> Web site: http://highgate.comm.sfu.ca/~rcini/classiccmp/
>> /************************************************************/
> I have a couple, I'll see if they use different transistors.  It's a 
> simple probe and just saturates the transistors.  I would guess that they 
> can be replaced with any general purpose switching transistors as long as 
> you match up PNP or NPN (2n2222 & 2n2907 ar my favorites).
> If either of mine use different transistors I'll follow up.
> I like the fact that the power lines can be isolated so it's easy to test 
> for voltage/amperage etc.
> Randy
> www.s100-manuals.com

I just checked and mine are TB-2's with no transistors (four IC's instead).

I just use them as straight extenders with easy to access bus pins & power 
separation.  I have an HP logic probe that I like.

You might post on comp.os.cpm to see if anyone else has any TB-1's.


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