Mega-floppies with mini-capacity
If you've been around personal computers for a few decades, you'll remember when floppy disks were, well, floppy. The dual 5.25-inch drives in the Osborne 1 used those flexible, black-sleeved disks, the decendants of earlier 8-inch floppies.
That oh-so-convenient port below the drive could house extra floppies (click to enlarge)
The original machine accepted only single-density disks with the amazingly miniscule capacity of 92KB. A double-density, factory-installable optional card, however could just about double that capacity, bringing it up to 182KB.
Trust me, if you want an Osborne 1, you want this optional double-density card (click to enlarge)
According to Oldcomputers.net, the double-density option allowed the floppy drives to also read disks formatted as Xerox 820 single density (82KB), Cromemco single density (80KB), IBM Personal Computer (156KB in the CP/M-86 format), and DEC VT-180 (171KB).
Here are a few views of the full-height 5.25-inch drives in the Osborne 1:
The front of the drive (click to enlarge)
The back (click to enlarge)
The bottom, complete with belt drive (click to enlarge)
Looking into the drive from the top, with floppy inserted (click to enlarge)
As large as these floppy drives now appear, they were compact when compared to the 8-inch drives in my teardown of an S-100 system that I built oh, so many years ago.
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COMMENTS
caps
I made that mistake twice myself but it was on the same day. I was examining a power supply with a really big al-elec 200V cap. It discharged on me. After I picked myself up I made the stupid assumption that now that it had kicked my ass it must be fully discharged. It wasn't.
The really amazing fact was....
...that the OS fitted on a single density 5.25 inch disk! What happened? Oh ya M$ happened, now you need >1Tb disk just to get started.
Fond memories
Owned the Rev A myself. And did have the external monitor as well as the 300 baud Osborne pulse dialing modem that fit into the floppy holder slot by the port. The Rev A had double density single sided drives where the original had single density. So everyone cut the notch in their floppies so we could turn them over and use the backside. My Osborne I ran: Turbo Pascal, COBOL, LISP, C, Z80 Macro Assembler in addition to the normal package and the plethora of add ons through the many BBS CP/M sites. At school, armed with a 300 baud modem, I did my mainframe work via Wordstar and uploaded it to save valuable "dollar" allotments on the school's mainframe. I was the envy of my dorm since 128 scrollable display is good enough to display the majority of mainframe output which was formatted for a maximum 132 character line printer. I made my own modifications to OSWYLBUR to handle the strange Osborne I modem... and many of us replace the CP/M shell with ZCPR, a command replacement with more features. I even hacked in a pulse dialing modem routine in place of the built in DIR command, since most people used a directory listing program from disk instead. I also programmed a game using the Software Toolworks C compiler where you flew around the screen and turned asterisks into boxes. The asterisks would kill you if you ran into them and the boxes were like walls, so as you played your ability to move about the screen decreased. What fun! I also wrote a mainframe 370 assembler in macro Z80 assembler. This allowed me to do a lot of my labs without using valuable compute time... just had to upload the final product. In high school, I developed a text adventure game (ala Infocom) where you had to solve chemistry problems to get through obstacles. In my junior year of college I wrote a small BBS in assembler for my Technical Writing class.
Great machine... I wish I had never given it away. It was very useful. It was fun keeping my dorm mates up all night as they listen to my TTX 1014 daisy wheel printer typing away....
It's Easy To Fix
Because, as you have a vertical line, you must have EHT for the CRT which comes from the line output transformer. This means the line output stage is working, its just the line scan coils that are disconnected, that will almost certainly be a dry joint on the PCB where the scan yoke leads connect or possibly at the scan coupling capacitor or line linearity coil. It can't really be much else other than an o/c scan coupling capacitor.
How do I know this? well, the college I worked for had lots of Osbornes and I used to repair them when they broke down. Most common fault was the extension card for the double density floppies working loose (these things were carried between rooms regularly which probably explains that), next was the display which could fail to work due to dry joints at the line output transistor connections or by the vertical line due to joints as described earlier.
Once I had to make a new system rom for one (by copying a good one from another machine) as the suspect one was partly corrupt (would boot to the Osborne startup screen but would intermittantly fail to load the o/s from disk) -- that took a while to diagnose.
One other task I had to do was calibrate all the floppy drives so that disks were interchangeable between all machines -- there were quite a few that would not reliably read disks from other machines until this was done.
Most of our Osbornes worked with external monitors (to ease eyestrain on the students).
When carrying machines between rooms I always carried two at a time, that way both arms stretched by the same amount :-) happy days indeed.
