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How can I tell if my SMD disk head is crashing?

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  • c f
    I ve been working for a while on reviving/rehabilitating an old CDC 9762 disk drive (each disk is a stack of 5 14 platters, with the middle 3 having 5 data
    Message 1 of 14 , Aug 11, 2011
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      I've been working for a while on reviving/rehabilitating an old CDC 9762 disk drive (each disk is a stack of 5 14" platters, with the middle 3 having 5 data surfaces and 1 servo surfaces - the drive has 6 read heads). I finally got to the point where the drive was cleaned up, so I spun up a disk pack and manually loaded the heads by just disconnecting the servo coil and moving it with my hand (the manual says this is okay for testing).

      When I loaded it, everything was fine for a minute or so, but then I began to notice a high-pitched whining noise coming out of the drive. I retracted the head assembly, stopped the disk, and attempted to inspect it and the head assembly. Everything looked fine as far as I can tell (the disk is a bit difficult to examine, as you need to look at it through the tinted plastic of its cover). I then retried the same procedure, and the high pitched whining noise started again right away when I loaded the heads.

      Does anyone know if that noise means one or more of the read heads is contacting the disk? Or could it just be a whistling noise produced by the head being close to the surface? The disk cabinet had been lined with a thick layer of noise-deadening foam that I had to remove, and I've never really worked with one of these before, so I'm not sure what it's supposed to sound like. Any advice would be appreciated.


      -Chris
    • Dave
      When these disks were in common use I seem to remember that the Customer Engineer had a way to remove the dust cover and had some kind of arrangement with
      Message 2 of 14 , Aug 11, 2011
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        When these disks were in common use I seem to remember that the Customer Engineer had a way to remove the dust cover and had some kind of arrangement with mirrors to check the pack. However its been a long time since I worked with these.
         
        However I do seem to think a high pitched squeal meant head contact.
         
        It was far to easy to wipe out several drivers with a bad pack......
         
        ... or by sitting a drive next to a closed off chimney so it sucked all the soot from the chimney in. 
         
        Dave 
        -----Original Message-----
        From: midatlanticretro@yahoogroups.com [mailto:midatlanticretro@yahoogroups.com] On Behalf Of c f
        Sent: 12 August 2011 04:36
        To: midatlanticretro@yahoogroups.com
        Subject: [midatlanticretro] How can I tell if my SMD disk head is crashing?

        I've been working for a while on reviving/rehabilitating an old CDC 9762 disk drive (each disk is a stack of 5 14" platters, with the middle 3 having 5 data surfaces and 1 servo surfaces - the drive has 6 read heads). I finally got to the point where the drive was cleaned up, so I spun up a disk pack and manually loaded the heads by just disconnecting the servo coil and moving it with my hand (the manual says this is okay for testing).

        When I loaded it, everything was fine for a minute or so, but then I began to notice a high-pitched whining noise coming out of the drive. I retracted the head assembly, stopped the disk, and attempted to inspect it and the head assembly. Everything looked fine as far as I can tell (the disk is a bit difficult to examine, as you need to look at it through the tinted plastic of its cover). I then retried the same procedure, and the high pitched whining noise started again right away when I loaded the heads.

        Does anyone know if that noise means one or more of the read heads is contacting the disk? Or could it just be a whistling noise produced by the head being close to the surface? The disk cabinet had been lined with a thick layer of noise-deadening foam that I had to remove, and I've never really worked with one of these before, so I'm not sure what it's supposed to sound like. Any advice would be appreciated.


        -Chris
      • Mr Ian Primus
        ... Eek. That sure does sound like a head crash... ... You can remove the dust cover to get a better look. I m not sure about the smaller packs, but on the
        Message 3 of 14 , Aug 12, 2011
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          --- On Thu, 8/11/11, c f <christopher.h.fenton@...> wrote:

          > When I loaded it, everything was fine for a minute or so, but then I
          > began to notice a high-pitched whining noise coming out of the drive.

          Eek. That sure does sound like a head crash...

          > I retracted the head assembly, stopped the disk, and attempted to
          > inspect it and the head assembly. Everything looked fine as far as I can
          > tell (the disk is a bit difficult to examine, as you need to look at it
          > through the tinted plastic of its cover).

          You can remove the dust cover to get a better look. I'm not sure about the smaller packs, but on the 300mb disks, look inside the center spindle - there will be a round hole in the center. By inserting something into that hole (like a pen), you can disengage the ball bearing catches that hold the top cover on, and lift off the dust cover. From there, use a flashlight to check for scratches on the disk surface.

          > I then retried the same procedure, and the high pitched whining noise
          > started again right away when I loaded the heads.

          That sure seems to point to a head crash, since it only whines when the heads are loaded. You should also be able to inspect the heads themselves. Look for any oxide scrapings or buildup. Did you clean the heads before you tried loading them?

          It's possible you're hearing something else... but a head crash should sound like metal on metal. A real terrible head crash would result in lots of brown oxide dust. Examine the pack for any trauma.

          Even if it did crash, all is not lost - heads do turn up. I know a guy that might have some. I've never done a head replacement though - but it is documented in the manual (and it's a lot of work...).

          -Ian
        • c f
          Darn, I was hoping the heads might just make some kind of whistling noise when loaded or something. I didn t notice any kind of oxide flakes/chunks/powder
          Message 4 of 14 , Aug 12, 2011
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            Darn, I was hoping the heads might just make some kind of whistling noise when loaded or something.


            I didn't notice any kind of oxide flakes/chunks/powder inside the dust cavity when I removed the pack (although I have not tried wiping the inside with a clean white cloth to check for really fine particles yet). I will look for a way to remove the dust cover - I haven't been able to figure out how to get around the interlock thing yet (although I haven't tried much).

            If you lift up the drive's main shell, there is a little window that lets you look into the drive cavity and see both the disk platters and the head assembly if you shine a light into it, although it was impossible to determine if a head was making contact or floating just by looking.

            I do actually have a 2nd drive (in pretty bad condition) that happens to have a full set of heads, as well as 1 spare head still in a box. I'm not sure if the 'servo' head is identical to all of the others, but I believe it is. I also have a tester with head alignment card, as well as the little head adjustment tool thing, and a CE pack for calibrating things. Unfortunately I'm also pretty pressed for time.

            One final comment - I reconnected the voice coil and attempted to let it go through its automatic startup process. The drive powers up, gets up to speed, and then attempts to do a 'load seek' operation, where the coil drives the head assembly forward about 2 inches or so, and then retracts quickly and triggers the 'fault' light. No whining noise or anything, though. I think this means that the servo head is failing to detect the dibit pattern on the out



            -Chris

            On Fri, Aug 12, 2011 at 7:31 AM, Mr Ian Primus <ian_primus@...> wrote:
             


            --- On Thu, 8/11/11, c f <christopher.h.fenton@...> wrote:

            > When I loaded it, everything was fine for a minute or so, but then I
            > began to notice a high-pitched whining noise coming out of the drive.

            Eek. That sure does sound like a head crash...


            > I retracted the head assembly, stopped the disk, and attempted to
            > inspect it and the head assembly. Everything looked fine as far as I can
            > tell (the disk is a bit difficult to examine, as you need to look at it
            > through the tinted plastic of its cover).

            You can remove the dust cover to get a better look. I'm not sure about the smaller packs, but on the 300mb disks, look inside the center spindle - there will be a round hole in the center. By inserting something into that hole (like a pen), you can disengage the ball bearing catches that hold the top cover on, and lift off the dust cover. From there, use a flashlight to check for scratches on the disk surface.


            > I then retried the same procedure, and the high pitched whining noise
            > started again right away when I loaded the heads.

            That sure seems to point to a head crash, since it only whines when the heads are loaded. You should also be able to inspect the heads themselves. Look for any oxide scrapings or buildup. Did you clean the heads before you tried loading them?

            It's possible you're hearing something else... but a head crash should sound like metal on metal. A real terrible head crash would result in lots of brown oxide dust. Examine the pack for any trauma.

            Even if it did crash, all is not lost - heads do turn up. I know a guy that might have some. I've never done a head replacement though - but it is documented in the manual (and it's a lot of work...).

            -Ian


          • c f
            Last sentence should read ...outer edge of the disk surface.
            Message 5 of 14 , Aug 12, 2011
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              Last sentence should read "...outer edge of the disk surface."

              On Fri, Aug 12, 2011 at 8:36 AM, c f <christopher.h.fenton@...> wrote:
              Darn, I was hoping the heads might just make some kind of whistling noise when loaded or something.


              I didn't notice any kind of oxide flakes/chunks/powder inside the dust cavity when I removed the pack (although I have not tried wiping the inside with a clean white cloth to check for really fine particles yet). I will look for a way to remove the dust cover - I haven't been able to figure out how to get around the interlock thing yet (although I haven't tried much).

              If you lift up the drive's main shell, there is a little window that lets you look into the drive cavity and see both the disk platters and the head assembly if you shine a light into it, although it was impossible to determine if a head was making contact or floating just by looking.

              I do actually have a 2nd drive (in pretty bad condition) that happens to have a full set of heads, as well as 1 spare head still in a box. I'm not sure if the 'servo' head is identical to all of the others, but I believe it is. I also have a tester with head alignment card, as well as the little head adjustment tool thing, and a CE pack for calibrating things. Unfortunately I'm also pretty pressed for time.

              One final comment - I reconnected the voice coil and attempted to let it go through its automatic startup process. The drive powers up, gets up to speed, and then attempts to do a 'load seek' operation, where the coil drives the head assembly forward about 2 inches or so, and then retracts quickly and triggers the 'fault' light. No whining noise or anything, though. I think this means that the servo head is failing to detect the dibit pattern on the out



              -Chris


              On Fri, Aug 12, 2011 at 7:31 AM, Mr Ian Primus <ian_primus@...> wrote:
               


              --- On Thu, 8/11/11, c f <christopher.h.fenton@...> wrote:

              > When I loaded it, everything was fine for a minute or so, but then I
              > began to notice a high-pitched whining noise coming out of the drive.

              Eek. That sure does sound like a head crash...


              > I retracted the head assembly, stopped the disk, and attempted to
              > inspect it and the head assembly. Everything looked fine as far as I can
              > tell (the disk is a bit difficult to examine, as you need to look at it
              > through the tinted plastic of its cover).

              You can remove the dust cover to get a better look. I'm not sure about the smaller packs, but on the 300mb disks, look inside the center spindle - there will be a round hole in the center. By inserting something into that hole (like a pen), you can disengage the ball bearing catches that hold the top cover on, and lift off the dust cover. From there, use a flashlight to check for scratches on the disk surface.


              > I then retried the same procedure, and the high pitched whining noise
              > started again right away when I loaded the heads.

              That sure seems to point to a head crash, since it only whines when the heads are loaded. You should also be able to inspect the heads themselves. Look for any oxide scrapings or buildup. Did you clean the heads before you tried loading them?

              It's possible you're hearing something else... but a head crash should sound like metal on metal. A real terrible head crash would result in lots of brown oxide dust. Examine the pack for any trauma.

              Even if it did crash, all is not lost - heads do turn up. I know a guy that might have some. I've never done a head replacement though - but it is documented in the manual (and it's a lot of work...).

              -Ian



            • Mike Loewen
              ... So, how many of us have actually done head replacements? I used to replace heads on HP 7920/7925/7933/7935 drives. The 7920/25s required an external disk
              Message 6 of 14 , Aug 15, 2011
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                On Fri, 12 Aug 2011, Mr Ian Primus wrote:

                > Even if it did crash, all is not lost - heads do turn up. I know a guy
                > that might have some. I've never done a head replacement though - but it
                > is documented in the manual (and it's a lot of work...).

                So, how many of us have actually done head replacements? I used to
                replace heads on HP 7920/7925/7933/7935 drives. The 7920/25s required an
                external disk exerciser and alignment pack:

                http://www.hpmuseum.net/images/7925-40.jpg
                http://sturgeon.css.psu.edu/~mloewen/Oldtech/Media/Diskpack1L.jpg
                http://www.hpmuseum.net/images/13354-60005-42.jpg
                http://www.hpmuseum.net/images/13354A-40.jpg

                The 7933/35s had an internal microprocessor for diagnostics:

                http://www.hpmuseum.net/images/7935-40.jpg
                http://sturgeon.css.psu.edu/~mloewen/Oldtech/Media/Diskpack2-1L.jpg
                http://en.wikipedia.org/wiki/File:HP7935_disc_drive_heads_circa_1983.png


                Mike Loewen mloewen@...
                Old Technology http://sturgeon.css.psu.edu/~mloewen/Oldtech/
              • c f
                I actually have a field test unit (exerciser) and alignment pack for this drive, as well as a whole set of heads sitting in another drive (and one spare one
                Message 7 of 14 , Aug 15, 2011
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                  I actually have a field test unit (exerciser) and alignment pack for this drive, as well as a whole set of heads sitting in another drive (and one spare one still in a box), but I'm not really sure about the procedure for doing alignment.

                  -Chris

                  On Mon, Aug 15, 2011 at 9:39 AM, Mike Loewen <mloewen@...> wrote:
                   

                  On Fri, 12 Aug 2011, Mr Ian Primus wrote:

                  > Even if it did crash, all is not lost - heads do turn up. I know a guy
                  > that might have some. I've never done a head replacement though - but it
                  > is documented in the manual (and it's a lot of work...).

                  So, how many of us have actually done head replacements? I used to
                  replace heads on HP 7920/7925/7933/7935 drives. The 7920/25s required an
                  external disk exerciser and alignment pack:

                  http://www.hpmuseum.net/images/7925-40.jpg
                  http://sturgeon.css.psu.edu/~mloewen/Oldtech/Media/Diskpack1L.jpg
                  http://www.hpmuseum.net/images/13354-60005-42.jpg
                  http://www.hpmuseum.net/images/13354A-40.jpg

                  The 7933/35s had an internal microprocessor for diagnostics:

                  http://www.hpmuseum.net/images/7935-40.jpg
                  http://sturgeon.css.psu.edu/~mloewen/Oldtech/Media/Diskpack2-1L.jpg
                  http://en.wikipedia.org/wiki/File:HP7935_disc_drive_heads_circa_1983.png

                  Mike Loewen mloewen@...
                  Old Technology http://sturgeon.css.psu.edu/~mloewen/Oldtech/

                • Dave McGuire
                  ... I ve done it on DEC RL01/RL02 and RK05 drives. -Dave -- Dave McGuire Port Charlotte, FL
                  Message 8 of 14 , Aug 15, 2011
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                    On 8/15/11 9:39 AM, Mike Loewen wrote:
                    > So, how many of us have actually done head replacements? I used to
                    > replace heads on HP 7920/7925/7933/7935 drives. The 7920/25s required an
                    > external disk exerciser and alignment pack:

                    I've done it on DEC RL01/RL02 and RK05 drives.

                    -Dave

                    --
                    Dave McGuire
                    Port Charlotte, FL
                  • jack99rubin
                    I suppose that s better than doing it _with_ DEC RL01/RL02 and RK05 drives. A certain cheesy picture comes to mind - I m sure you know which one I mean. : )
                    Message 9 of 14 , Aug 15, 2011
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                      I suppose that's better than doing it _with_ DEC RL01/RL02 and RK05 drives. A certain cheesy picture comes to mind - I'm sure you know which one I mean. :>)

                      [Sorry, slow day in the office while I wait for servers to smoke.]

                      Jack

                      --- In midatlanticretro@yahoogroups.com, Dave McGuire <Mcguire@...> wrote:
                      >
                      > On 8/15/11 9:39 AM, Mike Loewen wrote:
                      > > So, how many of us have actually done head replacements? I used to
                      > > replace heads on HP 7920/7925/7933/7935 drives. The 7920/25s required an
                      > > external disk exerciser and alignment pack:
                      >
                      > I've done it on DEC RL01/RL02 and RK05 drives.
                      >
                      > -Dave
                      >
                      > --
                      > Dave McGuire
                      > Port Charlotte, FL
                      >
                    • Dave McGuire
                      ... Heh...you ve heard the story about my old VAX 8700, haven t you? ;) (if not, no, I ain t gonna tell it here! ;)) -Dave -- Dave McGuire, AK4HZ New
                      Message 10 of 14 , Aug 15, 2011
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                        On 08/15/2011 04:39 PM, jack99rubin wrote:
                        > I suppose that's better than doing it _with_ DEC RL01/RL02 and RK05 drives. A certain cheesy picture comes to mind - I'm sure you know which one I mean. :>)
                        >
                        > [Sorry, slow day in the office while I wait for servers to smoke.]

                        Heh...you've heard the story about my old VAX 8700, haven't you? ;)

                        (if not, no, I ain't gonna tell it here! ;))

                        -Dave

                        --
                        Dave McGuire, AK4HZ
                        New Kensington, PA
                      • B Degnan
                        ... I am due for computer to pop....don t jinx me! Change subject, change subject!
                        Message 11 of 14 , Aug 15, 2011
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                          At 05:00 PM 8/15/2011, you wrote:
                          >On 08/15/2011 04:39 PM, jack99rubin wrote:
                          > > I suppose that's better than doing it _with_ DEC RL01/RL02 and
                          > RK05 drives. A certain cheesy picture comes to mind - I'm sure you
                          > know which one I mean. :>)
                          > >
                          > > [Sorry, slow day in the office while I wait for servers to smoke.]
                          >
                          > Heh...you've heard the story about my old VAX 8700, haven't you? ;)
                          >
                          > (if not, no, I ain't gonna tell it here! ;))
                          >
                          > -Dave

                          I am due for computer to pop....don't jinx me! Change subject, change subject!
                        • s100doctor
                          ... if a head had made physical contact with a platter, there would be some kind of circular trail on the platter. The heads are designed to float above the
                          Message 12 of 14 , Aug 30, 2011
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                            --- In midatlanticretro@yahoogroups.com, c f <christopher.h.fenton@...> wrote:
                            >
                            > I've been working for a while on reviving/rehabilitating an old CDC 9762
                            > disk drive [many platters and heads]

                            > When I loaded it, everything was fine for a minute or so, but then I began
                            > to notice a high-pitched whining noise coming out of the drive.

                            if a head had made physical contact with a platter, there would be some kind of circular trail on the platter. The heads are designed to float above the platter ALMOST like an airplane wing - hydrodynamic it's called, the air is dragged under the head and lifts it up. More like a surfboard on a wave.

                            It's possible what you are hearing is bearing noise - some bearing at speed, having lost its lubrication decades ago, is now whining.

                            So the diagnostics are

                            1) look very very carefully at the disk pack for any circular patterns. I'd photograph the hell out of it, then compare it after some use to see if there are changes. YOu might look for a lousy signal from one head, assume that's dragging, but that's tricky.

                            2) see if you can spin the platter at speed without loading the heads. The bearing should not care if the heads are there, I think. But it may make some difference in loading the motor. Hard to guess...

                            3) find someone who ran (or runs now) these suckers, see what they remember about noise. There's something about the whine of a hard drive with noisy bearings, versus the screech of a head as it scrapes across the platter until it's flung into orbit....(sigh) those were the days...

                            Herb Johnson
                            retrotechnology.com
                          • c f
                            It wound up being an actual head crash, and once I figured out how to get the dust cover off to look at it, I could see a ring scraped into the bottom-most
                            Message 13 of 14 , Aug 31, 2011
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                              It wound up being an actual head crash, and once I figured out how to get the dust cover off to look at it, I could see a ring scraped into the bottom-most data surface. I wound up being able to successfully clean the head and get it functioning again.

                              As for the disk drive - I'll do a longer write-up on my website at some point, but a quick summary:

                              -The control electronics were basically shot, and I didn't have schematics for the drive, so I wound up disconnecting everything but the analog read-amplifier/head-select board. I built a robot that clamped onto the positioning voice-coil and manually stepped the read-head assembly forward (at 5200 steps/inch, vs. 400 data tracks/inch), and built a simple ADC connected to an FPGA that buffered copies of the data tracks for every head on every step.

                              I now have a super high-resolution 'magnetic image' of the disk, and I'm going to try to do some signal processing to see if I can recover anything useful from it.

                              -Chris

                              On Tue, Aug 30, 2011 at 10:24 PM, s100doctor <hjohnson@...> wrote:
                               



                              --- In midatlanticretro@yahoogroups.com, c f <christopher.h.fenton@...> wrote:
                              >
                              > I've been working for a while on reviving/rehabilitating an old CDC 9762
                              > disk drive [many platters and heads]


                              > When I loaded it, everything was fine for a minute or so, but then I began
                              > to notice a high-pitched whining noise coming out of the drive.

                              if a head had made physical contact with a platter, there would be some kind of circular trail on the platter. The heads are designed to float above the platter ALMOST like an airplane wing - hydrodynamic it's called, the air is dragged under the head and lifts it up. More like a surfboard on a wave.

                              It's possible what you are hearing is bearing noise - some bearing at speed, having lost its lubrication decades ago, is now whining.

                              So the diagnostics are

                              1) look very very carefully at the disk pack for any circular patterns. I'd photograph the hell out of it, then compare it after some use to see if there are changes. YOu might look for a lousy signal from one head, assume that's dragging, but that's tricky.

                              2) see if you can spin the platter at speed without loading the heads. The bearing should not care if the heads are there, I think. But it may make some difference in loading the motor. Hard to guess...

                              3) find someone who ran (or runs now) these suckers, see what they remember about noise. There's something about the whine of a hard drive with noisy bearings, versus the screech of a head as it scrapes across the platter until it's flung into orbit....(sigh) those were the days...

                              Herb Johnson
                              retrotechnology.com


                            • s100doctor
                              ... That s VERY impressive work. Any chance you can put it up on a Web site and show it? If you put a few tracks of binary data up on the Web, some number of
                              Message 14 of 14 , Sep 1, 2011
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                                --- In midatlanticretro@yahoogroups.com, c f <christopher.h.fenton@...> wrote:
                                >

                                > -The control electronics were basically shot, and I didn't have schematics
                                > for the drive, so I wound up disconnecting everything but the analog
                                > read-amplifier/head-select board. I built a robot that clamped onto the
                                > positioning voice-coil and manually stepped the read-head assembly forward
                                > (at 5200 steps/inch, vs. 400 data tracks/inch), and built a simple ADC
                                > connected to an FPGA that buffered copies of the data tracks for every head
                                > on every step.
                                >
                                > I now have a super high-resolution 'magnetic image' of the disk, and I'm
                                > going to try to do some signal processing to see if I can recover anything
                                > useful from it.
                                >
                                > -Chris


                                That's VERY impressive work. Any chance you can put it up on a Web site and show it? If you put a few tracks of binary data up on the Web, some number of us might advise as to how to decode it. At that point it's an exercise in software, and some people do a LOT of that sort of decoding, just for fun. Certainly, more people that those who can jump-start a hard drive as you have. Congratulations!

                                Herb Johnson
                                retrotechnology.com
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