Re: New member with early HP computers

Paul Berger

On 2019-08-25 3:09 p.m., silverray.russia@... wrote:

Thank You!
Unfortunately I have no any working parts for substitution.
Sure I reassembled the entire device and cleared slots by ethanol.
Is there a circuit  for memory module with signal check points?
I checked up the signals on internal slot (I think it's a part of 9825A model with system ROM module) and saw some signal activity on it.



I have spare parts but I am a long way away from you.

The B model has the OS ROMs along with most of the option ROMs and system RAM on one board (A24).  The T model has a second board (A25) with just RAM and a state machine that allows some of the RAM to overlay ROM.  This second board if present can be disconnected for trouble shooting.

The long ROM slot towards the right side of the machine is the slot for the 9825A OS ROM on the same circuit board along the front there are 4 slots for option ROMs.  Since most of the option ROMs are built into a B/T, only the Mass Storage, and Matrix ROMs will work all others will be ignored.


The only schematics that I know of are Tony Duell's hand drawn schematics found at but they do not have labeled test points you need to figure that out for yourself from the logic.

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