HP 9915A

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. 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