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Old 10-18-2007, 04:06 PM
Cappellanus Cappellanus is offline
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Join Date: Jul 2007
Posts: 24
Default IC-99 Mystery (modification)

I see talk about IC-99 (the un-used chip) getting hot. There is a bit of a mystery regarding this, but I really think the original machines *DID NOT* have a chip in this place.

I think the original Kenbak-1's, produced both by John Blankenbaker and CTI just left this extra spot empty, no chip at all. My evidence? Look at the below board (online) at the Nova-Scotia computer museum. See
This is actually a CTI labeled machine (so one of the later produced ones) and it clearly shows an empty spot where IC-99 goes.

But Eric Klein's machine at
(which I think was where much of Grant's information came from) has an IC placed in this spot. Now look closely: On the back of Eric's machine, there are some cut traces, and jumper wires placed between the extra IC and the rest of the circuit. Notice that these jumper wires are slightly different looking than the original power and switch/light wires, suggesting later modification.

I tried to follow this, but it appears that Eric's machine had some sort of modification. Has anyone tried to schematic this out, to see what his modification does? It appears to me that some extra function is made to start or stop the machine, as this modifies the start/stop flip-flip state circuitry.

Anyone have any ideas what they were trying to do here? You can see the modified machine wiring really well on Eric Klein's web site. I think it would be quite reasonable to just leave this chip out of the kit.
Attached Images
File Type: jpg temp3.jpg (38.0 KB, 561 views)
File Type: jpg temp5.jpg (43.2 KB, 561 views)

Last edited by Grant Stockly; 09-10-2012 at 09:17 PM.
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