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.
Paul.
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
