ard at p850ug1.demon.co.uk
Wed Jun 9 15:47:38 CDT 2010
> Ok, I found it on EBay, but I consider it a rescue. :)
> This is an HP 9836 Model 200, a machine I've been looking to find for
> quite some time. It's a Motorola 68k-based workstation that was
> targeted (I believe) at the scientific market. It runs a proprietary
> OS and has several languages available for it. My next goal is to try
> and generate diskettes for it, which is not going to be easy until I
> finish getting my IBM PC set up for use at home.
They are nice machines. I have 2 of them (a 9836A and a 9836CU) along
with the closely-related 9826. And a couple of other machines in the
range -- the 9816 (built into the monitor case) and the 9817 (a 'shoebox').
Anyway, back to the 9836. To get inside, there are 4 large screws on the
underside. The top cover then lifts off. There's a motherboard flat in he
bvottom of the case, which as well as connectors for the other boards,
contains trhe HPIB, keyboard controller and some of the address decoder
circuitry. Plugged into the motherboard are the expansion backplane (8
DIO slots), the CPU board, the floppy controller and the PSU regulator.
There are 2 more PCBs under the left-hand disk drive which are the video
display circuitry (the top board is for the graphics display, the lower
board for the text display).
Several CPU boards have been used in these machines. Most of them contain
a 68000 CPU and some RAM (which is auto-addressed . And the boot ROMs.
If at all possible, get a machine with boot ROM 3.0 or later. Those can
boot from any device (internal drives, HPIB drives, SRM network, even
bubble mmemory (!)) whereas older versions of the ROM can only boot from
the internal drive. I believe there is a boot disk (it's part of the SRM
system) that allows older machines to boot from anything, though. And
note that alas the later ROMs are larger than the older ones, so it's not
simply a matter of getting the images and burning a couple of EPROMs to
upgrade an older machine.
 In these machines, RAM starts at the top of the address space and
builds down. The expansion RAM cards have to be addressed by DIP
switches. At part of the power-on self-test, the machine scans down
throught the RAM. When it fails to get a DTACK/, then hardware on the CPU
board automatically sets the address of the RAM on the CPU board to fit
immediatately below all the RAM it's found.
The latest CPU board contains no RAM, but it does have a 68010 processor
and an MMU circuit. This is fitted to the -U machines (U == Unix, these
machines can run HP-UX). If you have this board, you need at least one
expansion RAM card.
The floppy cotnroller uses a Western Digital IC. A couple of points.
Firstly, there are spearate cables from each drive to the controller
board. The drives have their MX jumpers fitted, so the outputs are always
enabled. The controller monitors things like the WrProt signal from each
drive to detect disk changes. The cable for drive 0 is soldered to the
board, the one for drive 1 is plugged in. This is because the same
cotnroller is used in most single-drive 9826s, whereupon the drive 1
cable is not fitted. There is a 256 byte sector buffer on the disk
controller board. It's a pair of either 2112s or 2114s (with 2 address
pins grounds). I mention this becvuase if you hve the latter RAM and have
internal disk problems, you know where to look :-) (Yes, I did have this
problem on my 9836CU).
The power supply is quite friendly in some ways, but a paiu to test on
dummy load. The basic design is that there's a transformer, a little PCB
at the back containing the voltage selector switches and a rectifier (the
TO3 can is a double diode, nothing more), and a smoothing capacitor. This
gives about 30VDC to the regulator board which contains swithcing
regulators to produce +5V, +12V and -12V.
The problem comes in testing it. The regualtor board has 2 sets of edge
figners. One plugs into a chassis-mounted connector carrying the DC input
from the smoothing capacitor. The other plugs into the motherboard and
carries the outputs. Now, since the mothrboard contains considerable
circuitry, including a programmed 8041 microcontroller (for the keyboard
interface), you don't want to use that as a dummy load.
What I did was make up a test box. A die-cast box with a couple fo edge
connectors on top, load resistors, lapms and voltage test sockets on all
the outputs and a pair of input sockets to power it from my bench supply.
Then I can just plug the PSU regualtor board in that and run it out of
the machine. But hten I have 3 of these machines to maintain. It's
probably too much work to do if you only have one.
A few comments now on the 9826 in case anyone has one. It's very similar
inside. Early models had a floppy controller that could only handle one
drive and a lower-current PSU, but I have never seen these. Most of them
have the same boards as are used in the 9836. The video system is very
different, of course, (a monitor PCB -- which contains just the
horizontal and video amplifier cirucits, the vertical circuit is on the
text video PCB) mounted in the base of the machine in front of the
motherboard, a text video PCB standing vertically behind the CRT and a
graphics board on top of that, screwed to the top of the CRT cage.
A word of warning. The CRT in the 9826 is _not_ rimbanded (the ones in
all 9836s are). If you have to work on the CRT area of the machine, take
great care, an impolosion is likely to be unpleasant.
As for expansion, there are 8 DIO slots. These uise the same connectors
as the S100 bus, but different signals (obviously) and smaller PCBs. The
signals are essentially the 68K bus with a few extras. 4 of the slots can
take boards with external connectors (interfaces, etc), the 4 between
them can take things like RAM, ROM, bubble memory, DMA controller, etc.
These machines have a built-in HPIB interface, but nothing else. I think
an RS232 interface (HP98626 or even better HP98628, which is
Z80-controller and does intenral buffering) is almost essential. An
HP98622 GPIO card (16 bit parallel in and out) is useful too. There are
many other interfaces and add-ons, inclduing ROM boards containing BASIC
or HPL, more HPIB interfaces, and even a bubble memory board.
> There's more information available at
> http://www.hpmuseum.net/display_item.php?hw=3 and I have a photo
There's an HP serivce manual which is a boardswapper guide, but is
probably worth reading. The only thing I really disafgree with in it
(other than boardswapping :-)) is the procedure fro removing the CRT from
a 9826. I find it a lot easier to remove the keyboard and then the bezele
assembly, then put the latter face down on the bench, remove the CRT
mounting band, and lift the CRT out. It takes alittle longer than the HP
method, but it's much less likely to damage the CRT.
There's also a set of unofficial schematics which may be useful if you
have to fix the thing.
You also want to read the manauls for the language you are using
(probably HP BASIC 5.x). There are a lot of interesting features...
On Bitsavers, you want to look at the _pascal_ system manuals. Some them
cotnain a lot of low-level programming information. And the 'breadboard'
interface manual which describes the DIO bus.
As for software, be warned that he disk images on the Australian museum
site are geernally for 3.5" disks. You can't dump them to 5.25" disks for
the internal drives. If you have a HP9122 or similar (and boot ROM 3.0 or
later) then there's no problem, you can boot from that and transfer the
software to the interal drives later.
Do watch the power-on tests. The error messages are not always taht
clear, but they will pick up a lot of problems. If something eems 'not
right' then you need to debug the hardware.
Let me know if you need any help. I've done a bit with these machines.
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