Help Appreciated Identifying Unusual HP-41 ROMS


About 10 years ago I bought a large lot of HP-41 stuff on Ebay. Included were some unusual ROMs. They've been sitting in a box for years and I am going through all my stuff trying to catalog it.

I have two ROMS that I suspect are HP-41 Diagnostic ROMS. I also have one keyboard overlay that appears to be for a Diagnostic ROM. The two ROMS behave a little differently when inserted in the HP-41.

Both ROMs are blank except for hand written sticky labels. The first one is labeled with a sticker 'P. Diag' on the bottom, and a small round sticker '3/' on the top. When inserted in an HP-41, and the -41 turned on, it immediately beeps 3 quick beeps "Dah-dit dit", and "SELECT TEST" flashes continuously on the display. Most keys don't seem to do anything, but pressing 9 gives "SRV MOD TEST" for a few seconds and then "SM-2B OK". 8 gives "GEN ROM TEST" and then "TM-2C OK" apparently testing the Timer ROM (-41CX). 2 gives "STS REC 0000", USER give "PRESS R/S", and when you do, "Printer TEST", which errors out (no printer connected). 3 gives "EOL TEST" and it too errors out. PRGM and ALPHA give "<AUTO>", but I don't know what it is doing.

The second one is labled "Diag ROM" on a sticker that is where a normal branded label goes, and it has a small red round sticker with a D on it and a small white retangular sticker with "BW" on it, both handwritten. When it is inserted, it beeps the same as the other one, but says "CPU OK" before blinking "SELECT TEST". Many more of the keys do things, and the 9 key gives "SRV MOD TEST" for a few seconds, and then "SM-1:C". There are some others, but these are the ones that have my attention right now.

Did HP release multiple Service ROMS? What are these? Any help graciously accepted.

Dan Grelinger


HP didn't "release" any service modules, but they did produce several. The ones you have are described in the service manual, which is on the MoHPC DVD or CD set.


I have recently received my copy of the HP Museum DVD's. I checked the HP-41 Service Manual, and the "Diag Rom" that I have behaves almost exactly as the ET-11966 is described. It appears to be a later version of the Diagnostic ROM, and the keyboard overlay that I have almost exactly matches the one illustrated, but mine has a few additional keys defined.

The second ROM "P Diag" performs much differently. It seems to only have General ROM, Service ROM and Printer Tests available to it. The other keys don't respond or execute the other tests.

It appears that the overlay has functions for both of the ROMs, the Diag ROM and the Printer Diag. I'll have to dig out my printer and test it!




Hi Dan,

Please reffer to this Article regarding different service ROM's.

In short, the first ROM you've described is an ET-11968 Printer Diagnostic (SM-2:B stands for Service Module version 2B). I know it quite well since I extracted its .ROM image file a few days ago. (details here, by the bottom of the post.

The second module is the ET-11966 HP41-C Service Module. If you can show a scan from the related overlay, it will be easy to determine which module is it intended for.

Best regards from the Canary Islands.



Here is the overlay.

It appears that it was created to support both the standard service module, and the printer service module, having key labels for both. Thanks for the link it was helpful!


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