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Thread: Fixing Commodore 1541 drives

  1. #1

    Default Fixing Commodore 1541 drives

    Heh,

    sometimes I wonder if I'm out of my mind. I ordered six failed commodore 1541 drives
    yesterday from ebay from one seller. And that's not all, from previous six I ordered, half
    are still not fixed. And they're not free either... well, if you like fixing things, that's probably
    what you will (try) to do!

    But, since I'm now eager to get my hands on the new drives to fix, I had a look at no#4 of
    the previous set. It is fairly early model I guess, serial number is 002279 and the board also
    looks early one. In fact, the early drives had bug from the factory, and this one has been bug fixed
    at some point of its life.

    First look at the drive: It seems to boot (but way too quick, the red light comes on and goes out very quick
    to what you would expect to). However, drive mechanics were not moving at all during the boot sequence.
    Seller had also mentioned bad smell of the drive.

    That is a good hint, the smell. Tantalum cap C15 is usual suspect and sure enough, the cap also looked
    externaly fried at closer inspection. I cut one leg of that C15 and it did have effect! Now the drive mechanics
    came alive, when the drive is turned on!

    Load attempt will now result 'Device not present' -error. The UB4 rom has been replaced. Maybe some version of speed dos or jiffy ?
    How would either of these behave during boot up - as mentioned above, this drive boots really really quick. The red light turns
    on for just very short and also spindle starts and stops much faster than standard drive.

    Anyway - as it was obvious that this is modded, I tried by replacing original 901229-05 rom and now the drive boots up normally.
    I could perhaps still use that modded rom, if I knew what it was. Of course, I would need to upgrade C64 as well to match it.

    Now I got the drive to respond to load command, but it got stuck at 'Searching for...' step.
    Very familiar fault and UA1 (7414) chip is the likely suspect. I have had several drives with this issue fixed by changing this chip to a working one.

    A closer inspection revealed to me, that UA1 chip had already been replaced some time of the drives life, but the replacement had been
    soldered directly to the pcb. I had to remove the chip again. I always do it by using solder wick and solder paste, it gets mostly all of the
    solder away and I can remove the chip without cutting its legs. And hopefully I do not damage the pcb in the process.

    I removed then the 7414 chip and tried to clean the pcb. The old solder had some brownish goo almost like rust or glue in the pcb surface.
    I tried to carefully cratch it away from there. I suspect some of the contacts had been damaged in the earlier chip removal and found out
    that at least one trace was broken between UA1 and UB1. Had to put extra jump wire there to fix broken trace after soldering back the new
    socket. it makes no sense to solder new chips the the pcb, sockets are so cheap.

    Installed new 7414 chip and drive is back to life ! Also test loaded Uridium and it did load just fine.
    In the end, I cleaned the drive head and greased the rails. Head was not stuck, but a little stiff and the
    bicycle grease made it very smooth and light to move around. I have to still find tantalum cap, I should have
    some spares to fix up C15 and then I can finally close the cover for the drive and call #4 drive fixed .

    To sum up, this drive was an easy fix. It is not always like that. Sometimes the faults
    lead to wrong direction and I end up banging my head against the wall. I hope to be able to fix up
    more than one of the coming six drives, but one is better than none. I might keep writing here
    the progress and my struggle with them, when I have received them.

    0.jpg1.jpg2.jpg3.jpg

    5.jpg
    6.jpg
    7.jpg

  2. #2
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    I've edited your 7.png to show the shaft where I add Blue Loctite to prevent the Collar
    from moving on the Shaft. That should help keep it from moving. I used a small screw
    driver to hold the drop until I got it positioned at the intersection of collar and shaft.

    The RED area is the Stepper Shaft.

    Larry


    7.jpg
    Last edited by ldkraemer; January 28th, 2020 at 06:34 AM. Reason: typo

  3. #3

    Default

    Thank you Idkraemer! I will note that on my service from now on.

    Tonight has been spent on other duties besides Commodores, but I did
    have a chance to put new tantalum cap on the drive mentioned in my previous post.

    Also gave a good wash to the drive cover. Who knows where many of these old drives
    have spent last few decades! Many that have come to me are outright filthy. But, a good
    wash makes miracles.

  4. #4
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    VintageVic,
    Sure No problem. If some day in the future, you prove some of the TIPS to be
    100% true, be sure to drop me a PM. I'd be glad to know they also helped you
    in your C-64 repairs.

    One other thing, I just thought of. I used to use Ghostbusters as my test loading
    software for the Floppy Drives. If a Drive I worked on loaded and ran Ghostbusters
    I declared the Drive as good. That was good enough for me, and the Drives owner.


    Larry

  5. #5
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    Do you only buy the Alps-mech based drives to rescue? I've found that almost all Mitsumi-mech based 1541's have dead heads. Out of a dozen that I own, 10 have dead heads.

  6. #6

    Default

    Quote Originally Posted by rittwage View Post
    Do you only buy the Alps-mech based drives to rescue? I've found that almost all Mitsumi-mech based 1541's have dead heads. Out of a dozen that I own, 10 have dead heads.
    I have found the exact same issue with Mitsumi mechanics drives. And yes, I only buy
    alps drives. Mitsumi drives would be good as spares for the case and pcb, but sellers
    don't make difference, they price the drives just the same with Alps models. Therefore,
    I prefer Alps mech drives.

    Once I got lucky, I accidentally bought Mitsumi drive. I was almost certain
    that I ended up buying drive with bad head, but in that case it was not head issue after all.

    I agree with that statistics of yours, most of Mitsumi headed drives it is the head that is open.

  7. #7

    Default

    UB4 ROM (901229-03 or 901229-05) failure is pretty common on 1541 drives.
    Replacements have often been made to EPROM chips, but I found that EEPROM
    works better for me. No need for UV lights for erasure or special power supplies or
    expensive (>20€ for a programmer feels expensive to me) eprom programmers for EEPROMs.

    What you need is Arduino nano (I got mine from less that 2€ from China), and
    needed couple of logic chips and ic sockets to build EEPROM programmer all cost peanuts also.
    Project was moderately challenging, not an easy one, but not impossible either, eventhough
    I had never used arduino before. Schematics for EEPROM programmer was freely available
    on internet but the programmer code did not work for me (or I did not know how to use it).
    Editing the example made it possible to write ROM dump to EEPROM chip, atmel at28C64
    in this case. It can hold 8kB roms. I found the project very satisfying to learn about
    shift registers and about how RAM/ROM chips actually work.

    There were steps along the way, where I did mistakes, but yesterday I had finally finished
    all the bugs and got it right. 1541 accepts the new EEPROM chips with 28 -> 24pin socket adapter.
    Ultimately, I wanted a cheap source of spareparts for frequently failing ROM chips.
    You can get 10x atmel EEPROM chips for around 5$ (china / ebay). I'd say that
    the goal is reached =).

    Furhermore, there is very short step forward from here to trying out jiffydos.
    Me likey !

    eeprom.jpg
    a.jpg
    b.jpg

  8. #8
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  9. #9
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    Default

    Quote Originally Posted by ldkraemer View Post
    I've edited your 7.png to show the shaft where I add Blue Loctite to prevent the Collar
    from moving on the Shaft. That should help keep it from moving. I used a small screw
    driver to hold the drop until I got it positioned at the intersection of collar and shaft.

    The RED area is the Stepper Shaft.

    Larry


    7.jpg
    I guess that you find the blue loc-tite holds? We always used to drill and pin these at the shop. I would think the constant track 0 rattle would knock loc-tite out after a little while...

  10. #10
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    Of the many 1541's I did back in the day, I never got one back that had the Blue Locktite.
    Maybe I was just lucky. But, there were enough being used in schools that I'd think at
    least one would have come back.


    Larry

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