11 Aug
2021
11 Aug
'21
9:05 a.m.
On 8/11/21 10:18 AM, Mark G Thomas wrote:
What do you use to connect an 8" drive to a
PC?
Hi Tom,
On Wed, Aug 11, 2021 at 09:37:24AM -0500, Tom Uban wrote:
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.
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.
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