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Thread: Macintosh 512k 400k disk drive not reading/formatting

  1. #1

    Question Macintosh 512k 400k disk drive not reading/formatting

    I picked up a 512 with an external drive and some other goodies a few days ago. Great find!
    Predictably, both the internal and external drive had jammed ejector mechanisms.
    I carefully cleaned and lubricated them, and now both eject disks just fine. The external drive also reads and writes disks normally.
    However, the internal drive won't read or format disks.

    I've done a lot of debugging on this, and here are the current symptoms:
    - The internal drive won't boot off a known good disk. It runs two cycles of trying three speeds, and then ejects.
    - When inserting a disk while booted, the internal drive will fail to format the disk. The disk just spins up, and is ejected right away with an erase failed dialog.

    I checked the following:
    - The read head stepper rotates and the head moves accordingly, it's not jammed.
    - The optical alignment sensor works (No click of death)
    - I spent about 30 minutes adjusting the optical alignment sensor (radial alignment)
    My thinking is, if the radial alignment was off, it would still be able to format disks and use them, just that those disks wouldn't work on other drives.
    Since it refuses to even try formatting a disk, I'm thinking something else is wrong.
    I've googled for an hour and couldn't find anything else. Ideas?

  2. Default

    Are you trying to debug the internal drive with the shield between the floppy and the CRT removed?

    -Mike Willegal

    Quote Originally Posted by Mac View Post
    I picked up a 512 with an external drive and some other goodies a few days ago. Great find!
    Predictably, both the internal and external drive had jammed ejector mechanisms.
    I carefully cleaned and lubricated them, and now both eject disks just fine. The external drive also reads and writes disks normally.
    However, the internal drive won't read or format disks.

    I've done a lot of debugging on this, and here are the current symptoms:
    - The internal drive won't boot off a known good disk. It runs two cycles of trying three speeds, and then ejects.
    - When inserting a disk while booted, the internal drive will fail to format the disk. The disk just spins up, and is ejected right away with an erase failed dialog.

    I checked the following:
    - The read head stepper rotates and the head moves accordingly, it's not jammed.
    - The optical alignment sensor works (No click of death)
    - I spent about 30 minutes adjusting the optical alignment sensor (radial alignment)
    My thinking is, if the radial alignment was off, it would still be able to format disks and use them, just that those disks wouldn't work on other drives.
    Since it refuses to even try formatting a disk, I'm thinking something else is wrong.
    I've googled for an hour and couldn't find anything else. Ideas?

  3. #3

    Default

    The disk drive is outside the machine, to the right of it when looking from the front. As far as the internal drive cable will reach.

  4. #4
    Join Date
    Jan 2014
    Location
    Northfield, MN USA
    Posts
    194

    Default

    Well, you could swap the external mechanism into the machine and declare partial victory

    Is the felt pressure pad missing from the non-working drive?

  5. #5

    Default

    Felt pad is present and looks fine on the defective drive.

  6. #6
    Join Date
    Apr 2018
    Location
    Los Angeles, CA
    Posts
    645

    Default

    So I just had this problem and it ended up being the internal floppy cable was bad. A thought is to remove the working external drive and plug it in to the internal cable to confirm that it's the drive and not anything else.
    -- Brian

    Systems: Amstad PCW 8256, Apple IIe/II+/Mac+/Mac 512k, Atari 800/520STFM, Commodore 64/Amiga 3000/PET 4032/SX-64, IBM PS/1 2121-B82, Kaypro II, Osborne 1, Tandy 1000 SX, TI-99/4A, TRS-80 Model 4 GA

  7. #7

    Default

    I did just that, I got a happy mac (more than with the dead drive) and then a sad mac with the code 0F0064.
    Fiddling around with the dead drive using the external drive cable, I got nowhere.

  8. #8
    Join Date
    Apr 2018
    Location
    Los Angeles, CA
    Posts
    645

    Default

    Quote Originally Posted by Mac View Post
    I did just that, I got a happy mac (more than with the dead drive) and then a sad mac with the code 0F0064.
    Fiddling around with the dead drive using the external drive cable, I got nowhere.
    So I think i'm reading this correctly:

    1) With the Internal drive hooked up, both internally and externally, it won't read a disk/boot up.
    2) with your external drive hooked up externally you can read and write disks properly to it.
    3) (this is the part i'm confused on)... with the external drive hooked up internally, it will read the disk but then fail with a 040064 Error.

    So based on a lot of things I was reading lately to get my 512k working these are the things I ran across. I don't know if any of these help or not.

    1) Internal floppy cable might be bad. If all of the above is true, this sounds like one of your issues but I guess check the continuity of the pinouts on the cable to confirm.
    2) Which ROM's are in your MAC+ and model number of your drives. 'A' roms only work with certain models of drives.
    3) On the external floppy connection, confirm all the voltages of the system are in-line. From top left to right, Pin 6 should be +5v, 7 & 8 should be +12v. Confirm those are in range (not too low or too high) and adjust accordingly.

    The end result is that the 'good' external drive should work as an external drive or an internal drive. If that isn't the case, something else is wrong. If that is the case, then it's the internal drive. It could be both as well (bad internal drive and something else as well).
    -- Brian

    Systems: Amstad PCW 8256, Apple IIe/II+/Mac+/Mac 512k, Atari 800/520STFM, Commodore 64/Amiga 3000/PET 4032/SX-64, IBM PS/1 2121-B82, Kaypro II, Osborne 1, Tandy 1000 SX, TI-99/4A, TRS-80 Model 4 GA

  9. #9

    Default

    Update:

    I decided to put the working external drive into the 512. Turns out, it works fine in there if it's properly connected and has a solid ground (which I didn't have before when quickly testing.)

    After about an hour of fiddling with the radial alignment on the defective drive, I finally got it to boot a few times. It's still very finicky. Formats fail most of the time, and it still randomly has occasional failures reading known good disks.
    I don't have the tools to properly perform a radial calibration, so I'm just tweaking it blindly and hoping for the best.
    I think another problem is that I am testing with newer HD Sony 1.44MB PC diskettes. I know those can be tricky with some drives, and it probably doesn't make this any easier.
    For what it's worth, I've used 1.44 meg disks perfectly fine on my other 800k macs, and the 1.44 meg disk works fine in the good 400k drive as well.
    I have 1.44 meg disks I formatted to 800k 9 years ago and they still read fine. From what I understand the concern is that the older read/write heads have trouble magnetising the higher density flux on the newer disks.

    There is a local hacklab that has several oscilloscopes. How big of a project would it be to hook one up to this to do the calibration? Any literature available on doing that?

  10. Default

    Unless it is completely off, radial alignment shouldn't greatly affect formatting a floppy. It should only affect drive to drive compatibility. Since it sometimes works, you might still have a slightly sticky mechanism, which could prevent the head from getting properly positioned when seeking. Rotational speed could be a bit slow, which would prevent a track's worth of data from properly fitting. I can't remember if there is any adjustment for that. Since it sometimes works, a lower probability is some kind of problem in the electronics.

    regards,
    Mike Willegal

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