Opening HP-9825 ROM Cartridges


If you are wondering whats inside, here is a picture

more info on how to open them at



Looks like these cartridges can be hacked quite easily if one wanted to add more ROM to them. The solder pads are already there!


Sure, except that it's not an industry-standard ROM chip. It's a strange HP 16-bit wide ROM with multiplexed address and data, a built in address latch, decoder, and non-TTL signal levels. So you can't just add an EPROM or Flash chip; you'd need a daughter card with level shifters, and address latch, a decoder, and possibly some timing circuitry.

Edited: 18 June 2006, 4:48 p.m.


That's how I open them too (and for that matter, 9810, 9820 and 9830 cartridges come apart in the same way). Melting a little solder onto the head of the 'nail' improves heat transfer and makes it easier to get them apart. The 'nails' are an aluminium alloy, and solder doesn't stick to them.

To put them back together, I normally use countersunk self-tapping screws. Not original, but it sure makes it easier to take them apart again.

There are at least 2 types of HP9825 cartridge. One uses the HP custom ROM as you've discovered. The other uses a normal ROM chip, and a little TTL (address latch, address decoder). Note that the PCB in one type is fitted components-up, in the other type it's fitted components-down. This is somewhere in the schematics you have.

Possibly Related Threads…
Thread Author Replies Views Last Post
  opening hp 15c for repair FORTIN Pascal 4 2,012 10-12-2013, 10:35 AM
Last Post: FORTIN Pascal
  9815 data cartridge drive (also 9825 / 9845 / 85 / 87, and who knows what else) John Ioannidis 2 1,313 06-12-2013, 07:20 PM
Last Post: Craig Ruff
  Printing HP 9825 data Norman Pillsbury 3 1,558 06-01-2013, 10:08 PM
Last Post: David Ramsey
  98228A 9885/9895 ROM for 9825? Craig Ruff 4 1,594 05-15-2013, 07:18 PM
Last Post: Craig Ruff
  HP85 Programmable ROM cardtridge 82929A-service ROM not working- inaki 2 1,884 04-25-2013, 08:08 AM
Last Post: inaki
  shelf life time of a ROM, EEPROM, EPROM vs Mask Rom Guido (Canada) 6 2,982 01-11-2013, 04:09 PM
Last Post: Thomas Falk
  Big ROM - 41 System DEMO ROM Ángel Martin 5 2,567 10-16-2012, 05:28 AM
Last Post: Ángel Martin
  TI CC40 cartridges ... names of programs on them? Gene Wright 3 1,367 04-08-2012, 10:49 PM
Last Post: Palmer O. Hanson, Jr.
  opening HP 30B Harald 6 2,183 02-26-2012, 09:07 AM
Last Post: Marcus von Cube, Germany
  Opening a 100LX David Ramsey 4 1,510 11-29-2011, 12:34 PM
Last Post: Hubert Weikert

Forum Jump: