๐บ๐ธ Osborne 1: Part 3 (Gotek Install) [TCE #0507]
28Gave the keyboard a good clean ... shout-out to "Jenny" who assembled my keyboard on Monday 27-Sep-1982. I also replaced the three RIFA safety capacitors in the power supply.
I ordered some Gotek adaptor PCBs from PCBWAY and they arrived pretty quickly (there are other designs, see below).
The Osborne's floppy interface includes 5V and 12V on some of the odd-pins (normally all ground) which means [a] a separate power connection isn't required, and [b] an adaptor is required.
Interestingly, the left-hand drive (Drive A:) is at the end of the floppy cable and thus has the termination-resistor array and works on DS1 signal. This means that the right-hand drive (Drive B:) is in the middle of the cable and works on DS0. I couldn't see anywhere on the drive's motherboard where DSx setting was made.
I ended up replacing the RHS Drive B: and so I had to ensure my Gotek was jumpered for DS0, and also that the Osborne IMG.CFG file was installed on the USB drive.
https://github.com/keirf/flashfloppy/...
Finally, after finding some single-density disk images (ImageDisk IMD format) and converting them to HFE format for the Gotek, I was able to boot my Osborne 1!
Remember: you can switch Drive B: to become Drive A: and boot from it by holding [SHIFT]["].
Dave Dunfield's site with numerous disk images:
http://dunfield.classiccmp.org/index.htm
HxC Utility:
https://hxc2001.com/
I have collated some information here:
https://github.com/0ddjob/Osborne_1/
And, of course ... Flash Floppy:
https://github.com/keirf/flashfloppy
In Part 4 I'm planning on upgrading the BIOS from v1.4 to 1.44 and also adding in the 3rd party OZROM 1E.
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From Part 1:
Let's have a quick look at this Osborne OCC1 computer from 1981, a luggable Z80-based machine with 64KBytes of RAM, dual 5ยผ" floppy drives and a built-in 5" monochrome screen.
It only runs on mains power - as this one has come from the US but its power supply is very easily switchable from 120V to 240V.
It has an interesting array of ports on the front - full featured really: an external battery (DE9 socket), video output (edge connector), IEEE488 port, RS232 serial (DB25) and a modem port ... with modem.
That "EXT VIDEO" video output edge connector is very important - you either need a shunt to connect the top PCB signals to bottom, or a video output connector (with RCA socket) to allow video output on a larger screen. Without either, you will not get any video displayed on the internal screen!
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From Part 2:
None of the three disks I have will boot - I suspect that the CP/M system files aren't included on them so I need an actual CP/M 2.2 boot disk for the OCC1. You can switch to booting from Drive B: by holding [SHIFT]["].
The disks are labelled as "DD" ... double density ... but this requires an additional daughterboard inside the machine ... mine has none. So it appears to be "SD" or single density only.
I pulled the machine apart - wasn't too difficult, although you do need some space. It's definitely a lot easier than the IBM Portable PC to pull apart!
The 5ยผ" floppy drives are Siemens model "FDD 100-5" and use belts.
It came as no surprise that the power supply had a few RIFA capacitors used as class X safety filters ... and one had blown up. So I'll replace those whilst I have it apart: the main 0.1ยตF (100nF) that had blown and two smaller 0.01ยตF (10nF) that were starting to look a little iffy.
I know it's possible to buy a set of disks, but I should also be able to make my own images with the tools I have. I might try to get it running off a Gotek/Flash Floppy in the interim.
For that, this small PCB looks useful:
https://www.pcbway.com/project/sharep...
... or ...
https://github.com/WayneVisser/Osborn...
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https://karlcasey.bandcamp.com
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