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Thread: Restoring a Micropolis SCSI-1 drive

  1. #11
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    Quote Originally Posted by mR_Slug View Post
    have you got sg_utils? it might be able to probe the drive and get some further info, though may just tell you it's not ready.
    I thought that only worked with /dev/sg* devices, but I see from the web page it now works with /dev/sd*. I'll have to give it a shot.

    The ability to send start unit, stop unit, and other commands might also be useful.

  2. #12

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    Quote Originally Posted by smbaker View Post
    I did order a same model "tested good" drive from ebay, and assuming that drive does indeed "test good" when I get it, I'll try a controller swap.
    I wouldn't hold my breath. Most of the so called eBay (say 99%) "TESTED" listings are pure BS. They are listing them and rolling the dice it will work long enough for you for it to be out of the money back guarantee period. Out of the other 1% a good majority were tested when the item/stock came in - 30 to 40 years ago. It has now sat in the back, somewhere, for a few decades until someone at the shop noticed that the price of SCSI drives have gone way up and it is up on the auction block.
    Last edited by Shadow Lord; June 27th, 2020 at 11:46 PM.
    Current Wish List: 1. IBM 7531 Industrial Series PC 2. NEC MultiSync XL (JC-2001) Monitor 3. MicroSolutions MatchPoint AND/OR UniDOS card 4. Compaq 14" VGA CRT Monitor (the one that came with the SystemPro). 5. Stacker HW CoProcessor Board MCA BUS. If you have any of the above for sale please PM me. Thank you!

  3. #13
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    Spent my lunch messing with old HDDs again. Some success and some fail.

    1) The "tested good" drive did indeed test good.

    2) Of the two "bad" drives I had, I started with the one I cared the least about. The controller made absolutely no difference. Following djg's advice, I popped the cover. The heads were not seeking and were all the way on the inward side of the drive. I gave the head assembly a helpful nudge and it took off and seeked to the outer edge of the platters. Imaged this drive just fine!

    3) Now, of the bad drive that I cared about, I figured I was in luck and the same procedure would work again. No joy. Swapping the controller made no difference. Popping the cover revealed the heads along the inward side of the drive (again). However, nudging the head accomplished nothing. They weren't stuck, I can freely move them back and forth. There were some set screws that adjusted an inside and an outside stop, which (despite caution urging me to leave them the F alone) I decided to mess with. No luck there either. I tried nudging the head back and forth in tiny increments, but the drive never takes notice. Drive spins fine but does not seek. It still does the occasional slow down / spin up that it's been doing all along.

    So I saved a drive I didn't care that much about, but failed to save the critical drive...

    I've replaced three boards (controller, motor drive, and something up in the nose of the drive by the heads). There's no electronics left that I can replace other than three small transistor-size devices inside the spindle motor. Spindle motor appears to not be removeable so I can't swap it. These three transistor-like devices appear to be hall sensors, UG-3040U ? I'll try to snap a picture.

    @djg any ideas? You're the wizard whose advice so far saved one of the two drives.
    Last edited by smbaker; June 29th, 2020 at 02:34 PM.

  4. #14

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    When I was working on my RD53 moving the heads a large distance didn't work. The .007" shim did. I think the servo for the initial fine speed control is only a narrow band. I can't remember what the drive did when I moved the heads manually. Do you have a scope? It may be possible to see what the servo is seeing. I may be able to play with my drive some more this weekend to see if I can figure out more suggestions for you. Don't know how close the drive behavior will be but probably best shot.

  5. #15
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    Quote Originally Posted by djg View Post
    When I was working on my RD53 moving the heads a large distance didn't work. The .007" shim did. I think the servo for the initial fine speed control is only a narrow band. I can't remember what the drive did when I moved the heads manually. Do you have a scope? It may be possible to see what the servo is seeing. I may be able to play with my drive some more this weekend to see if I can figure out more suggestions for you. Don't know how close the drive behavior will be but probably best shot.
    Yeah, I have a scope, but not a clue where to connect it (nor exactly what to look for). Help here would be much appreciated.

    I did try nudging the head ever so slightly under the assumption the drive would take off and seek out to track 0 once it was over the right spot, but it never did. Maybe the scope is indeed exactly what I need, then we'll know we are over the right spot.

  6. #16
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    Also, if it's any use, test points in the vicinity of the head connector on the main controller board include:

    * SX, SY ... right next to the connector
    * SS
    * REV
    * VF
    * PQ, PX
    * VR
    * IM
    * X, Y

    I could just take a wild guess and attach a probe to SS, but I think I'll wait for @djg.

  7. #17
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    Fooled with it some more tonight.

    It feels like my hard drive thread has collided with my tape drive thread. Just like the tape drive's capstan roller had turned into black goo with approximately the consistency of wet jbweld, so had the hard drive's rubber bumpers inside the head assembly. I think this allowed the heads to move far enough out of position that there was a head crash, or other damage.

    I transplanted in the head assembly from the drive I was able to resurrect earlier this week into this drive. It still doesn't come up clean, but it at least behaves differently. If I push the heads outward eventually it will do a little seek, like it noticed the head had moved and wanted to resync it. This suggests to me that maybe it's reading something now from the servo track (particularly when I move the heads outward) whereas it wasn't reading anything before.

    Given there was a head crash, there could be platter damage, and it could be the drive just isn't viable anymore. Djg if you do get the chance this weekend, please send me a scope picture of a good servo track and I'll compare it to mine.

  8. #18
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    It's been an educational, but ultimately not successful experience.

    1) I did find what I believe is the servo signal on the SS pin. The transplanted head assembly was outside of the servo signal.

    2) I designed a fine adjustment jig (picture attached; published at https://www.thingiverse.com/thing:4521574) to allow the head to be adjusted until the servo signal reads good. The jig worked pretty well.

    3) While a scope can be used to verify a good signal, I find that once you get close enough there's a good chance the drive will take off and run with it.

    4) The drive now seeks out to track 0 (just like the other one that I repaired!) but unfortunately it sits out there at track 0 re-seeking every ten seconds or so. Drive reports status 02/22h/00, which according to documentation is "illegal function".. That particular error doesn't make a whole lot of sense to me. From the behavior I would have expected it to report some kind of seek error. Regardless, it clearly has some kind of problem out there at track 0.

    Anyhow, I suppose I should be happy that I managed to salvage the data on one of the two drives. It's been an interesting learning experience, and I thank those here who gave me tips that pointed me in the right direction. Were it not for the head crash and the need to replace the head assembly maybe I could have salvaged this image too.

    micropolis_jig_1280.JPG

  9. #19
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    Nice jig! Thanks for sharing all this!
    Torfinn

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