HP41 Circuit Diagram


I have three RIP full-nut HP41 (2 CV and 1 C). I believe at least one of them can be revived (Frankenstein way). I have found the HP41C circuit diagram, but the circuit boards I have are somewhat different: they have ILE/ILF series ROM/RAM IC´s not mentioned on the diagram I have. Can anyone help identifying these fellas? Can they be combined some way? Will I burn something if mixed them the wrong way?

Thanks in advance.


HP used higher density memory chips (both ROM and RAM) in later HP41s. That's essentially how they packed first the CV and then the CX into the same size case as the C.
At the logic board level, though, all boards have the same pinout (well, assuming they're not halfnut, since those machines don't have a separate logic board ;-)). You can swap them about without problems.
There is one caveat concerning the display driver, and a capacitor on the logic board (early display drivers need a different value), but if the display hybrid (at the top of the keyboard PCB) looks the same (the common one has 2 round black blobs of epoxy over the chips), then it'll be fine.
Later HP41 service manuals give half-a-dozen different versions of the logic board schematic using different types of ROM and RAM.


I have found there are at least 10 different versions of the CPU card for the 41C/CV/CX series. Different layouts, different chip combinations, etc. They all seem to be compatible. I have swapped the three chip piggybacks into six chip CPU's without any problem, etc.

Beware of the boards with the 1/4 watt resistor that lays on its side in the lower corner of the board (with the lead folded back along its length). These boards are thinner than the others and NEED those washers to maintain the proper pressure on the zebra connector. Standard boards were 0.065 thick. The thinner ones around 0.045. It is interesting that the standard HP washers are less than 0.010 thick... I have fixed several flakey machines by using thicker washers (0.020).


Hey, thank you guys. About the diagram and the ILE/ILF series IC´s: is there any address I would find reference for them OR, at least, the C/CV (full-nut, all right) schematics? I have lost my 41C schematics...


If you send me an e-mail message with a list of the chips you're interested in, I'll see if I can find at least pinouts for them.

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