HP9825 internal ROM?

[Gregory Beat]

Curious Marc has a complete set of YouTube videos on his restoration
of the HP 9825, due to Power Supply failure (no crowbar) damaging a number of ICs.

The Last video of the series shows fabricated of the PC Board for 
it’s missing Crowbar Circuit.
https://youtu.be/gIfJ30fPAOw

HP 9825 Crowbar Protection Circuit Project (Schematic, Parts, Gerbers, etc.
https://www.curiousmarc.com/computing/hp-9825-scientific-computer#h.xrov16yr03br

You can Order the PC Board from PCBWay
https://www.pcbway.com/project/shareproject/HP_09825_66552_Crowbar_Protecton_Circuit_for_the_HP_9825_Vintage_Calculator_a244bde6.html

greg
chicago
==
Date: Wed, 4 May 2022 16:40:13 -0400
From: Chris Zach
To: CCTalk mailing list
Subject: HP9825 internal ROM?

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