Zenith Z90

From: Jeff Kaneko <Jeff.Kaneko_at_ifrsys.com>
Date: Tue May 5 17:46:22 1998

<SNIP>

> Plugged into the CPU board is a 16K RAM expansion card (obvious), a
> triple RS232 port card (3 8250's) and a pair of disk controllers. One is
> a hard-sectored controller using a sync serial chip and the other is a
> double-density controller using a 1797. I've not figured out how they
> connect to the single internal drive and the 2 external drives.

The single internal drive plugs into the hard-sectored controller
board. There should be a short ribbon cable from the drive to the
board. The external drives should plug into a socket on the rear
apron of the machine (unless they didn't install the plug; then
you'll have to route the cable directly to the double-density
controller board).

I own an '89 myself, and they're pretty similar. It's been so long,
I'm straining my synapses to remember the keypress to boot off of the
external floppies. There is one keystroke that will cause the thing
to boot from the internal drive.

Make sure the fan blows really good, these suckers tend to overheat
(I knew a guy who ran it with the cover off, with a *BIG* muffin fan
pointed at the PSU). They also prefer filtered power-- we used to
screw up alot of floppies before we got a SOLA . . . .

Funny, you know last nite I was seriously thinking about resurrecting
the 'ol H-89, now that I have the space to do so. . . .

> That's pretty tight already, but there's more. There's a 3rd party
> graphics board fitted on top of the CRT (seriously). It links into the
> PSU/video cableform from the Terminal logic board to the monitor, and
> also into 8 of the RAM chip sockets on the CPU board. The RAMs you pull
> to plug in the cables go into the graphics board, which contains
> _another_ 16K of RAM as a bitmapped display buffer.

I dunno about this display board. There were a few graphix cards
built for these. I have some old magazines that may yield a clue . .
 
> I got some manuals with it. The most useful is a hardware reference
> manual for the basic computer - schematics/parts lists/circuit
> descriptions. Alas sheet 2 of the schematic is missing (it would show the
> terminal logic board and keyboard, I guess), but the circuit description
> is so complete that I could almost draw out the schematic from that
> alone. No schematics of the disk controllers either. There's also a CP/M
> manual/ disks and an HDOS manual set with disks. HDOS looks to be a
> little like RT11 :-). Oh, volume 2 of the HDOS set contains ROM sources
> for the H8, H88, H90, etc computers :-).

I may be able to help with the FDC print, assuming it's H/Z standard
issue (that's what I have). There were at least two other third-party
DS/DD FDC's for it. Zenith docs are good, but configuring CP/M to
work with the external 80-track drives can be a royal pain, unless
Zenith was nice enough to supply a pre-configured floppy (mine was a
Heathkit, so we had to do everything from scratch).

Unfortunately, I know almost nothing about H-DOS, but I think I have
some software for it hanging around here someplace. . . .

Jeff
Received on Tue May 05 1998 - 17:46:22 BST