Opening HP 71B ROM modules



Does anyone know if there's a trick to open HP 71B ROM modules (the edge-shaped modules for the front module ports)? Is it possible without destoying the case?

What do they contain? Any user-servicable (*g*) parts inside? What ICs do they hold? Has anyone experimented with creating (programming and replacing the EPROM with his own) modules? Is there a tutorial anywhere?

Thanks in advance.


There's not really a trick. They're ultrasonically welded together, so you have to slice them open. Whether that destroys them depends on what you mean by "destroy", and how careful you are.

There are no user-serviceable parts inside. There are anywhere from one through four actual ROM chips, but they're mounted chip-on-board and covered with epoxy, similar to 41 modules.

EPROM modules were sold by third parties. They used an EPROM in a windowed leadless ceramic chip carrier, and the module package was designed to leave the window exposed. There must have been a Saturn interface chip in the module as well, but I've never taken one apart.

HP had an interface chip to allow the use of bytewide memory chips on the Saturn bus. The third party card reader port memory modules use this chip in a rectangular plastic quad flat pack. The packaged part was too large for a front-port 71B module, but possibly the third-party RAM and EPROM modules may have used the HP chip as a bare die mounted chip-on-board.


You can force them open using a similar technique to that used to open HP-41 modules (

You won't find much inside though, they contain a small PCB with a custom HP ROM chip. Here is a picture from CHHU Chronicles V1N1 (Oct 84).


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