Xerox 820/II 8/16 Prom/Eproms ( Masters ) on e-bay

[Mark G Thomas]

Hi Tom,

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).

> 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):
> 
> http://bitsavers.org/pdf/xerox/820-II/firmware/

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.

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.

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.

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 
for $75.

Mark

-- 
Mark G. Thomas <Mark at Misty.com>, KC3DRE