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): >> >> 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. 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!
--tom
