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Thread: Commodore 900 restoration

  1. #1
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    Default Commodore 900 restoration

    I've had a bit of an adventure lately and I'm not done yet. After acquiring a Commodore 900 last year I finally had the time to look into it. Being that it was originally from Germany, the power supplies were supposed to be 240v but the previous owner did some work on them and thought the computer power supply was 120v but the monitor was 240v. As it turns out, the PC power supply had issues that were not easily diagnosed (it blew fuses) so I found a replacement in the Commodore PC10-II which worked. I had no idea until someone pointed that out to me. I then had issues with the monitor power supply so I found a replacement with the same specs (24VDC at 2.7A) and that worked like a charm.

    The ongoing issue has been the Miniscribe 3425 20MB MFM hard drive. It had a terrible squeak on start up and shut down and the stepper motor was locked up so I freed up the stepper motor and lubed both motors. The issue I have at present is that I am trying to archive off the data as it contains several demos and what appears to be the Coherent 0.7.3 source code that the C900 runs off of but the hard drive spins down after about 40 minutes or so. The drive light stays solid. The last time today it spun up again but the light stayed solid and that was it. I had to power it down.

    I ordered and MFM Emulator board from David Gesswein and I am hoping I can image the hard drive and reimage another Miniscribe 3425. I am unsure if it will be able to emulate the hard drive exactly as the Western Digital based controller (WD1003-CMD) is custom made for this computer and I believe it uses SASI commands to talk the MFM drive. Oh and to top it off, you cannot format a hard drive because there is no utility to do it. There is a ROM monitor program that I think may do it but I don't have that version.

    The floppy drive is working but it is a quad-density drive that might be talking GCR. I believe it's 96tpi but some have said it may be 100tpi. Long story short, nothing but a C900 can read those disks so even a backup won't help.

    So, suffice is to say, it's a project. It has Kermit at 9600 bps but by the time I can send stuff to a PC, the hard drive spins down.

    Regardless of the issues, I have been able to record some "hi-res" graphic demos that were used in the 1985 Hannover Fair CeBit in Germany. You can see some pictures and the videos are link at http://vintagecomputer.ca/commodore-900/

    While I am aware that I need to get the data off of this drive ASAP, I haven't found why the drive spins down with no errors and a solid drive light. Has anyone else seen this? I thought it might be heat related but I ran this with and without the computer cover and it still lasts about the same amount of time. The MFM emulator will come soon but I was just curious if anyone has seen this and has been able to fix it.

  2. #2
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    Honestly given how rare this data is and how fragile the drive is you should send it to a forensic agency that specializes in recovering data from the platters themselves. For example, secure data recovery.com

    I am sure Canada has similar services.

    If it costs too much, then do a go fund me. Tons of us would chip in to preserve this.

    The more you mess around with it yourself, the less recoverable it may become.

  3. #3
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    Floppy disks are floppy disks; it might be possible to archive those somehow, even if only flux transitions for analysis later. What make/model is the floppy drive? Any chance it uses the same format as an 8050/8250?

    Is there a full model number for that 3425 drive? If by chance it's a 'standard' model, maybe replacing the PCB might be an option to try.

    m

  4. #4
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    Quote Originally Posted by rpiguy2 View Post
    Honestly given how rare this data is and how fragile the drive is you should send it to a forensic agency that specializes in recovering data from the platters themselves. For example, secure data recovery.com

    The more you mess around with it yourself, the less recoverable it may become.
    Thanks for the reply. I have stopped touching it until I get the MFM emulator. I also acquired two more Miniscribe 3425 drives which I will try to use as duplicates of the hard drive once I am able to image the hard drive and hopefully re-image the newly acquired ones. I purchased two in case they are old and sound worse than this one. The original drive actually sounds pretty good. It's just this shutdown at around 45 minutes that is killing me.

    If David's MFM emulator doesn't work (I think it will), then I'll move onto the DREM. If that doesn't work then I'll talk to one of those places. The Coherent file system has issues. I tried to run a "check -s" against it and it reported some errors. I am also not able to run "tar" properly so I can't tar more than a few files and given the time limit I have, I am just stopping for now.

    What I was able to do was to run a "du" command and get a list of files, then Kermit them over. The list of files on this hard drive are here: http://vintagecomputer.ca/files/Comm...0/CONTENTS.TXT There is full source code for the operating system on his hard drive along with those demos. Some files I cannot get to because of file system errors but once I am able to clone the hard drive, I'll work on fixing the file systems. There is no "fsck" in the delivered version of Coherent 0.7.3 but the engineer had compiled a copy. I will only try this on a copy of the hard drive.

    Anyway, for now I wait for supplies before I touch it again.

  5. #5
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    Quote Originally Posted by MikeS View Post
    Floppy disks are floppy disks; it might be possible to archive those somehow, even if only flux transitions for analysis later. What make/model is the floppy drive? Any chance it uses the same format as an 8050/8250?
    There is a slight chance as it is GCR format but the 8250 has drives that are 100tpi. The computer had an 8250 floppy in the drive but I was not able to mount it. I did format several 96tpi floppies and they seemed okay. I have an 8250 and a 2031LP that I might try but for now, the hard drive re-imaging is the best option as it's fairly quick and I think the MFM emulator can do it within the 45 minutes or so.

    Quote Originally Posted by MikeS View Post
    Is there a full model number for that 3425 drive? If by chance it's a 'standard' model, maybe replacing the PCB might be an option to try.
    That is the full model number but I haven't checked the drive board to see if it's any different than a stock 3425. I don't think it is as the WD controller it connects to is completely custom. As I mentioned, I acquired two 3425 drives. One so I have a backup and the second to try to replace the board on the original drive. If that doesn't work, i'll just make a second copy.

    We'll see how it goes.

  6. #6
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    Interesting machine, story and videos! Thanks for sharing, and please keep us updated on any progress and / or further exploration.
    Torfinn

  7. #7
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    A status update:

    David Gesswein's MFM emulator saved the day. Not only did it successfully read/image my hard drive but I was also able to make an emulation file and ran the C900 on the MFM emulator for further exploration without the threat of imminent hard disk failure. To top this all off, I also used an "experimental" mfm_write tool to make two backups of my C900 hard drive on two identical Miniscribe 3425 hard drives I was able to procure!

    Unfortunately, my file system is a little messed up with some legitimate bad blocks but the MFM emulator was able to clean up many read errors with CRC error checking and correction. I still have to fix a small part of my hard drive but the loss of this is only source code and does not affect the computer running at all.

    Through further exploration, I was able to find and finally run a demo Windowing Manager that allows multiple windows to run. I have a picture of it here. Now I am really sad that the Commodore 900 didn't go any further but I am glad that with the MFM emulator's help, the hard disk is archived and backed up.

    C900 HRconsole.jpg

  8. #8

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    That is awesome. I've never seen a 900 in graphic mode, but it clearly lives up to its reputation.
    I use my C128 because I am an ornery, stubborn, retro grouch. -- Bob Masse
    Various projects and oddities: http://oldvcr.blogspot.com/
    Machine room: http://www.floodgap.com/etc/machines.html

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