HP Forum Archive 16

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Opening HP-9825 ROM Cartridges Message #1 Posted by Vassilis Prevelakis on 18 June 2006, 1:31 p.m. If you are wondering whats inside, here is a picture more info on how to open them at http://www.series80.org/HP9825 **vp

Re: Opening HP-9825 ROM Cartridges Message #2 Posted by Han on 18 June 2006, 1:56 p.m., in response to message #1 by Vassilis Prevelakis Looks like these cartridges can be hacked quite easily if one wanted to add more ROM to them. The solder pads are already there!

Re: Opening HP-9825 ROM Cartridges Message #3 Posted by Eric Smith on 18 June 2006, 4:45 p.m., in response to message #2 by Han 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.

Re: Opening HP-9825 ROM Cartridges Message #4 Posted by Tony Duell on 19 June 2006, 12:31 p.m., in response to message #1 by Vassilis Prevelakis 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.

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