Modifying the 4101

FPQ-6 Radar

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Contributed by Peter Main by email to PD, 20 September 2005

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At one stage, perhaps late 1964, there appeared an FCO for a wiring change to the RCA 4101 computer within the Q-6 radar. It involved perhaps ten wires on the backplane to be added, removed, or rerouted. The intention was to speed up the computer by removing a redundant timing cycle from some part of its operation, but after studying the documentation for the change (before implementing it) it became apparent to me that as written it made no sense. Further, it was not a matter of a simple typographical error - several of the specified wiring changes were clearly wrong. However, the intention behind the changes was clear, so it was possible to figure out what they should have been.

Monte Sala was at the Q-6 at the time. Monte was normally assigned to the DCS in those days, so I don't recall why he was up at the radar on that occasion. Perhaps it was for cross-training. Anyway, I discussed the FCO with Monte and he confirmed my suspicions about it. After some soul-searching, and a lot of encouragement from Monte, I decided to go ahead with what I believed the changes should have been. After all, if it didn't work I could always go back to the previous condition and simply tell NASA that their ECO was erroneous.

As it happened, the change worked just fine, and Monte and I congratulated each other. The computer did run slightly faster, just enough to be noticeable, though I doubt that it meant anything in terms of operations. I suppose I should have told NASA what I'd done, but I don't recall that I ever did.

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