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 . . .