My exhibit at HOPE:
I took an Osborne 1b ROM rev 1.4 to the 2600 magazine "The Last HOPE"
convention on July 19th, as part of a vintage computer demo. I originally
planned to exhibit an "original" version of the Osborne 1 (with the tan
chassis, also model rev v. 1.4), but that one had a bad A drive. "Insert
Disk in drive A and press RETURN" is as far as I could get.
Prior to the event I did attempt to replace the drive. First I had to see
what was going on inside of the machine. It takes about 10 minutes to
completely disassemble an Osborne 1, if you have a longish phillips-head
screwdriver. There are only three types of screws and clearly this machine
was made for field repairs.
Anyway.. once I got the system completely apart so that I could get to the
disk drives I learned that the drive gets it's 5v and 12v power from the
data cable, and there is no separate power connector like your
run-of-the-mill IBM PC drive. The drive's controller card had special
electronics for drawing voltage through certain pins in the dataline, etc.
In short, one cannot simply swap out an Osborne 1 disk drive and replace
with the drive from a Kaypro II or IBM PC. My choices appeared to be
either sacrifice a working drive and swap the electronics from the bad
Osborne drive, or simply find a replacement drive.
It was 11 PM, I had to be up by 6AM, and so I decided to take the Model 1b
Now here is why all of that trouble was worth it. At The Last Hope, I ran
into a guy who used to be an Osborne service tech. I got into discussing
the system I left at home with the bad A drive. He told me that a special
key combination, when pressed upon boot, would cause the system to boot
from the "B" drive. CP/M needs to boot from A, so A becomes B, B becomes A
when this bypass is activated. He tried for quite a while, but could not
find the key combo. But now I knew it was possible.
After he left I found the answer on http://vintage-computer.com/vcform/
...when pressed upon boot will cause the system to swap the drives.
The B drive (now "A") DOES boot, and now I can use the system with one
drive at least.
This is just one good reason to exhibit at VCF E this year. If you exhibit
you invariably run into someone with a tidbit of knowledge useful to your
projects, and visa versa.