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Monday, May 17, 2021
CONTINUITY: HP 9825 Repair Part 8: It Boots Again!
After digging into the tangled logic of the RAM board, simulating it with Logisim Evolution, the problem is narrowed down to an Intel 3242 dynamic RAM controller chip. This was was a single chip solution which handled multiplexing of row and column addresses as well as the refresh address to an array of dynamic RAM chips, and automatically kept track of the refresh address. This eliminated a handful of MSI chips in a memory board design. I used one in my 1979 M9900 64K RAM board.
Replacing the chip and…it boots!
Posted at May 17, 2021 12:23