On 8/11/21 10:18 AM, Mark G Thomas wrote:
On Wed, Aug 11, 2021 at 09:37:24AM -0500, Tom Uban wrote:
I have a Xerox 820. I don't know how to tell
if it is a -II or not. It is marked as U05-013264 September 1984.
You have an
820-II; the original 820 only has two ROMs (U63, U64).
Ok, I was going by the
appearance of my case being the older style. I had not considered the number
of PROMs, but now that you mention it, my old Ferguson Big Board (which was an 820 clone)
It powers on
and boots the monitor. Looking at the PROMs, they are labeled:
U33 5.0, U34 5.0, U35 5.0, U36 5.0, U37 4.01, U38 4.01
At least some of the ROMs appear to be available
here (along with other info):
I must have worked on mine right
before someone put those files on bitsavers.
I vaguely remember some alternate ROM version that supported a newer style
keyboard, and was incompatible with my older setup, but I do not remember
specifics. Labels in the e-bay photos also support that.
At some point, I need to ask someone to make me
bootable 8" floppies, but I suppose I need to
determine if it is 820 or 820-II first...
I can able to help you with floppies.
The floppies are standard
IBM 3740 Single Density and easy to write with Imagedisk software
and a PC-connected 8" drive.
What do you use to connect an 8" drive to a
My 820-II currently boots and runs from disk images on
SD cards, via
a Lotharek HXC floppy emulator, with appropriate cable wiring. I used
images found on the internet, and some I created from very old floppies
of mine using Imagedisk on a PC with an 8" floppy connected. I highly
recommend the Lotharek HXC floppy emulators. My only wish is the
display on the floppy-form-factor version were easier to read.
emulators look nice, but I am partial to the real floppy drives.
Both the swithing supply in my 820-II and it's
external 8" drive box
had failed. I replaced the supply in the 820-II case with a modern
switching supply that easily fit. The HV bleeder resister for my CRT
was arcing, so I replaced that. I replaced all the electrolytics on
the monitor board. I also replaced the sockets for my ROMs, as some
of their contacts "sprung" when I replaced the chips, but I do not
recommend doing this unless it is absolutely necessary and you have
good tools and practice.
I had not turned on my box for a number of years, but when
you posted, I decided to try it and it
worked perfectly, which I suppose is just lucky. I do have the tools and skills to work on
it if it
were to fail, but won't likely make changes unless it does.
The 820-II restoration was a fun and rewarding
project. It is well
documented, easy to work on. It was also my first ever CP/M computer.
When I was in high school, the 820 motherboards were readily available
It sounds like you had a good time, which in my opinion is the main goal!