HP-42S -- Memory Upgrade?


I just opened two HP-42S and fixed one (See "Re: HP-42s How To Open", elsewhere). I found pads for what looks like a spot for another surface-mount RAM or ROM chip on the PCB. It's two rows of 14, so another 28-pin chip could be placed there.

Does anyone know if this is for RAM? Does anyone know how to jumper it so it'll work? (There are several spots where interlaced traces allow for intentional solder bridge "jumpers" to be set.) Does anyone know the maximum RAM/ROM capacity of an HP-42S?

Heck, if I could install, say, 32K on a -42S, I'd be in some weird calculator Nirdvana . . .


In case anyone's interested, I tried a 32K chip in the "extra" memory location on my HP-42S circuit board. No combination of jumpers would make it recognize anything other than the ~6K of memory available normally. (I was able to break it temporarily, but fortunately I didn't seem to harm it permanently . . .) I'd guess the extra pads are for an alternate-source ROM and/or a different model calculator. (-17B or -27S, perhaps?)


Makes sense to have only a few PCB's with which one can make a whole range of models. Just swap ROMs and put in a bit of RAM, and hey presto! a new model is born!


Did you make photos of the opening of the calculator ? Just curious, how it looks like in the interior.


I've offered photos to David Hicks for inclusion in the Pioneer "Technology and Packaging" secion of the MoHPC. He's expressed interest, so (perhaps next week) I'll be taking a few shots of the Pioneers I have opened, and sending them along. You'll see 'em in the MoHPC "one of these days".

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