HP9825 internal ROM?

Paul Berger phb.hfx at gmail.com
Wed May 4 16:14:03 CDT 2022

The 9825B should have a board part number 09825-66524 with 16 DRAM chips 
and 10 24 pin ROM chips these ROM chips replace teh OS ROM module pluged 
into the right bottom of the machine and also most of the option ROMs.  
You may also have a second board with another 16 DRAMs a a lot of other 
logic that is the memory expansion.


On 2022-05-04 17:40, Chris Zach via cctalk wrote:
> Question for the group: I'm working on a HP9825B here. First thing I 
> did was take it apart, clean it, unplug all the power connections to 
> the board and test the power supply. Supply is good (values below) so 
> after checking the boards I put it together and powered it on.
> Note: I can see the lack of a crowbar circuit on the +5 line and would 
> be happy to install a crowbar circuit. Does anyone have a spare PCB 
> board as otherwise I'd need to order at least three of them to build one.
> Voltages are still good, however I get nothing on the display. The 
> CAPS LOCK does light up the caps lock light and it's cleared by 
> pressing Shift but that's about it.
> Question: Is there supposed to be a ROM board or cartridge inside the 
> unit by default? This one does not have one (the space between the 
> front of the CPU board and the 4 card edges on the front). Perhaps 
> that's the problem.
> If so is it possible to build a board that can contain a more modern 
> ROM with the system code on it?
> Thanks!
> Chris
> Appendix: Power supply voltages:
> Blue +25
> White -25
> Red +5
> yellow 11.97
> white/red -5
> white/yellow -12
> orange 7 volts

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