On 04/05/2022 21:40, 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?
CuriousMarc did a crowbar on youtube:
https://www.youtube.com/watch?v=gIfJ30fPAOw.
The circuit is available on his website:
https://www.curiousmarc.com/computing/hp-9825-scientific-computer#h.xrov16yr03br
The whole series was fun to watch (even though I don't have an HP9825)
Antonio
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Antonio Carlini
anto...@acarlini.com
