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

Tom Uban tom at
Wed Aug 11 11:05:59 CDT 2021

On 8/11/21 10:18 AM, Mark G Thomas wrote:
> 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).
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) only had
two PROMs.
>> 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 PC?
> 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.
The Lotharek 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 
> for $75.
> Mark
It sounds like you had a good time, which in my opinion is the main goal!


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