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Thread: Successful MFM Hard Drive Repair

  1. #1

    Default Successful MFM Hard Drive Repair

    I just thought I'd share my anecdote with you guys. I managed to get an IBM 5170 a while back in pretty clean condition around a year ago (and just found the original matching keyboard a few weeks ago, though it's missing half the numpad), and when I initially got it, it was occasionally booting. Often times, though, it would report a 17XX hard drive error. Eventually, it was constantly reporting 1701 at startup, with the drive spinning up, knocking the actuator against the stops a few times, and then shutting down the spindle motor.

    Just a couple of weeks ago, someone rekindled my interest in the computers, so I figured I'd get the 5170 set up again. Just as before, it fails to boot from the drive. I had the cover off the drive once before, just to see if I could spot anything visibly wrong. I could not.

    Since the drive now wasn't doing me any good in its current state, I figured, what the heck; I'll try to fix it. Being an early CDC drive (Magnetic Peripherals 94155, type 11) with the voice coil armature, I figured the armature bearings might possibly be bad, considering when I took the top cover off, the armature was not moved towards the spindle, but rather stuck in the middle of the cylinders. Not stuck as in stiction, but just not where it was supposed to. Again, the disk would come up to speed just fine, and the platters were very easy to turn. But moving the armature manually was rather difficult, and worst of all, there were rough spots in the travel.

    I carefully removed the armature assembly from the case and slid the heads out from the platters. This was a very delicate operation, and despite being careful, I popped a head off. Bummer... I didn't let that stop me though. I figured, what the heck...why not try gluing it back on? Not wanting to get fumes everywhere, I used nail polish instead of superglue, and managed to get the head back on seemingly without any issues.

    I then took the armature assembly entirely apart, flexible circuit board, heads and all. My goal was to get the bearings out and see about replacing them. I was able to tap the top bearing out without any difficulty. It turns out that the two bearings sandwich a spring inside. The axle itself has two grooves for holding the top bearing in with some snap rings. Thus, tapping on the bottom bearing forced the top bearing to come loose, leaving the bottom one in position. The bearings are .25" ID, .5" OD, for the curious.

    Lucky for me, it was the top bearing that was bad. Even luckier, just one surface of the bearing was bad. To make matters even better, the spring can push against the bearing to force the good bearing surface to be used, after turning the bearing over. Easy fix, right?

    So back in it went, this time, flipped over. I added some penetrating oil and 3-in-1 oil along the way for good measure, as I didn't want to leave the good surface unlubricated. Putting it back in was as easy as tapping it in with a small hammer, or in my case, a crescent wrench. I realigned the axle such that it was fairly centered.

    I reassembled the actuator assembly, and then came the tricky part (as if removing the heads from the assembly wasn't bad enough!): getting the heads over the platters. I had some fine tweezers that exerted enough pressure outwards to spread the arms apart, but I only had one pair. Plus, I only have two hands, and there are three sets of two heads. Then I engineered what I thought was a clever solution: wedge something in between the arms, rotate the armature into the platters, and the platters will push the wedges out. Once the wedges dislodge, they will spring towards the surface of the platters. So, that's exactly what I did, with some appropriately sized nuts from my parts bin.

    After maybe 20 screws later, the drive was all back together. Into the computer it went, and with the flick of the power switch, I nervously waited for the error codes. I would've waited a while, because...they never came! It went straight to GW-BASIC without any problems. The drive was loudly "flying" away (I would agree that they do sound like jet airplanes taking off) with the faint whirring of the actuator after the drive reached operating speeds. Of course, I didn't expect it to boot from disk, as I had no doubt messed with the alignment of the one head in relation to the others from gluing it on, as well as the armature in relation to the platters. Had it done that, I think I would have walked to my car, driven to GA, bought some lottery tickets, and patiently await some more good fortune.

    After getting the Advanced Diagnostics Disk for the AT, I low-level formatted the disk. A few bad spots popped up, but that was to be expected, of course. Partitioning it with FDISK and FORMAT came next, and they too reported some bad allocation units. But all in all, it went very well. MS-DOS 4.01 was next to install, and that went without any issues.

    Next thing you know, I have a booting 5170 from the original CORE International ATplus hard disk!

    I hope this was at least somewhat informational, despite the lack of pictures. To be perfectly honest, I expected to take it apart, screw something up terribly, put it back together to make it look good, and put the machine back in the closet. To have a booting machine (still no problems yet, too!) was the cake, and the icing on it, so to speak. All this to say, I didn't want to waste my time taking pictures during the repairs. Looking back, big mistake; some pictures would have certainly helped explain the spring and bearing situation inside the armature.

    Here is a not-so-good picture of the machine playing Tetris (I found that copy at the thrift store for a couple of bucks...brand new!).

    Let me know if you need any clarification on my process. Thanks for reading!


  2. #2


    Very impressive... did you take any photos along the way?

  3. #3
    Join Date
    Aug 2009
    Oslo, Norway
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    Well done!

  4. #4


    Wow. That's amazing. I am sad to see such a good repair done only for u to give it DOS 4.01. What a waste!
    Last edited by marcoguy; May 6th, 2012 at 05:34 PM.

  5. #5


    Quote Originally Posted by pearce_jj View Post
    Very impressive... did you take any photos along the way?
    Thanks! Again, I did not think to take pictures because I was not at all confident that it would work. Sorry!

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