HP9815 (was Re : prn plotters)

Brent Hilpert hilpert at cs.ubc.ca
Fri Feb 16 01:45:11 CST 2007

Tony Duell wrote:
> There are 2 versions of the HP9815 processor board. The original one uses
> 2112 RAMs (256*4), and 2Kbyte ROM chips. It's laid out for 8 such chips,
> only 7 are fitted (so 14K of ROM). This board can take a RAM expansion
> board that mounts on the track side (top) of the PCB at the rear edge.

I opened it up and the 7 ROM chips are pretty obvious, I must have
seen them before. The 6800 is marked only with HP's house number, so I'm
guessing I read something somewhere that told me it was a 6800 and left me 
with the impression there was only 2K of ROM.
14K of firmware code certainly makes more sense.

> I've had my 9815 totally apart, of course. If you're tempted to do the
> same, can I recmend against dismantling the keyboard. For one thing the
> PCB is held down by around 100 timy screws. And when you get the PCB off,
> the keycpas fall out and are a right pain to get back. Don't ask....

On the unit I have ~ 9 of every 10 of those tiny screws is instead a push-pin
inserted into the plastic, so the keyboard isn't about to come apart without a
high likelihood of breaking things. I'd rather have the screws, for cleaning
and potential repairs.

> Suffice it to day I had to send a panic e-mail to a couple of lists
> asking for the order of keycaps in part of the keyboard...

(.. or power it up, press the keys and find out what they do..)

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