HP 9915A

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Sat Jul 17 17:18:56 2004

>
> I recently aquired an HP 9915A computer/calculator which is the industrial
> version of the HP85.

I know it well. There are a few differences from the 85, of course. No
built-in printer, only 3 I/O slots, but a ROM drawer is built in (there
are 6 spaces for the HP ROM modules on the mainboard under the I/O cage).
There's also some kind of built-in EPROM module (a little daughterboard
with 8 sockets for 2716s (or 2732s if you move the soldered links), hung
off a microcontroller.

I assume you have the tape drive (this is technically an option) and the
frontpanel buttons (which are connected in parallel with the programmable
function keys on the keyboatd). The blue (IIRC) key is equivalent to shift.

> If any one has the keyboard and would like to sell it or trade for it email
> me.

Keyboards are much rarer than machines. Fortunately, the keyboard is just
an array of swtiches, the keyboard controller (same as in the 85) is on
the mainboard. Many of the 'chips' on the I/O card are diode arrays to
protect the keyboard controller from ESD damage.

I have a pinout of the DB25 for the keyboard (heck, I have a hand-drawn
schematic of the machine). Most of the keys are in a 8*10 matrix. Shift,
Control, and CapsLock (the last being a latching switch) have their own
inputs, the other side of those swtiches goes to ground. I can probably
find a keyboard matrix diagram somewhere (if only in the HP85 service
manual, it's the same layout).

The DA15 conenctor bascially carries the LED drive lines that are used
for the front panel indicators.

And the BNC connector is conventioal composite video at US TV rates
(RS170-like)

I refuse to tell you what the IEC 'kettle plug' is for :-). Note that
lovely bit of HP design where a flange on the cover fits round this plug,
so you have to pull the socket out before removing the cover. Neat.

Oh yes, the tape drive sufferes from the same gummy wheel problem as
other HP tape drives. You can strip it down like an HP85 tape drive, but
note that the tachometer lamp leads are soldered to the PCB (or at least
they are in my machine), not pushed into little sockets. Not a real problem.

-tony
Received on Sat Jul 17 2004 - 17:18:56 BST