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 Post subject: Deformation of dishes?
PostPosted: December 5th, 2018, 16:33 
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Many times HDDs encounters with bad sectors in certain areas of the HDD, and once the reading of the data was finished I was able to recover the bad sectors that were still applying vibrations to the HDD.
In none of these cases there were scratches on the HDD, so I assumed that it is due to deformations in the dishes.
I open this topic in case anyone can shed some light on this topic.
Right now I am recovering a HDD WD that has suffered a fall and the heads have it well but I get this problem. When I finish reading the HDD I will try to investigate more about this problem and expose it.

Greetings.

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 Post subject: Re: Deformation of dishes?
PostPosted: December 5th, 2018, 18:16 
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It is probably eccentricity issue.

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 Post subject: Re: Deformation of dishes?
PostPosted: December 5th, 2018, 18:22 
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labtech wrote:
It is probably eccentricity issue.

Is there a way to solve the problem?

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 Post subject: Re: Deformation of dishes?
PostPosted: December 5th, 2018, 18:25 
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Outside the scope of my experience, but I would say, at advanced level, you can test signal quality with oscilloscope while adjusting platter(s). Obviously can run into other issues with platter sync [depending on model] and so on.

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 Post subject: Re: Deformation of dishes?
PostPosted: December 5th, 2018, 18:30 
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Thank you very much for your interest.
Do you know or does anyone know a thread explaining the concept of eccentricity in HDD?

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 Post subject: Re: Deformation of dishes?
PostPosted: December 5th, 2018, 18:50 
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This is what happens when I submit the HDD to vibrations.
Attached video.


Attachments:
Nuevo Archivo WinRAR.rar [1.24 MiB]
Downloaded 17 times

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 Post subject: Re: Deformation of dishes?
PostPosted: December 5th, 2018, 21:07 
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Could you please explain what you do to "submit the HDD to vibrations."

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 Post subject: Re: Deformation of dishes?
PostPosted: December 5th, 2018, 21:50 
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labtech wrote:
Outside the scope of my experience, but I would say, at advanced level, you can test signal quality with oscilloscope while adjusting platter(s). Obviously can run into other issues with platter sync [depending on model] and so on.

Here's a handy guide. :shock:

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 Post subject: Re: Deformation of dishes?
PostPosted: December 6th, 2018, 3:53 
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Eccentricity in hard drives is more commonly referred to as "repeatable runout" (RRO). This can be due to tolerances in the track writing process. When the head tries to follow a track that is off-centre, the head wobbles.

"Non-repeatable runout" (NRRO) is the type of wobble induced by vibration in the server chassis, or an impact, or maybe even a worn bearing.

The following document describes how WD's enterprise drives handle rotational vibration:

Rotational Vibration Cancellation Technology in WD Enterprise Hard Drives:
http://www.wdc.com/wdproducts/library/other/2579-001079.pdf

Unfortunately the diagram in that document does not correctly illustrate RAFF.

Here is what it should look like:

Attachment:
WD_RAFF.gif
WD_RAFF.gif [ 42.98 KiB | Viewed 396 times ]

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 Post subject: Re: Deformation of dishes?
PostPosted: December 6th, 2018, 5:18 
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Thank you very much for the guides.
LarrySabo wrote:
Could you please explain what you do to "submit the HDD to vibrations."


What I do to make vibrations is to put 3 lower screws and tap them with the finger in the corners. I will try new methods.

I know it's very unorthodox, but when there are a few sectors left to read and I know it's not a scratch on the plate I do it and I get good results.

Must take into account:
1. It is a process that can damage the HDD.
2. I do it when I no longer have access to those few remaining sectors.

Surely there is some way to do it correctly, but I do not know it.

This is something that I am sure you know many and some of you have tried, but I can not recommend it to anyone.

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 Post subject: Re: Deformation of dishes?
PostPosted: December 6th, 2018, 9:23 
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mhp666 wrote:
Thank you very much for the guides.
LarrySabo wrote:
Could you please explain what you do to "submit the HDD to vibrations."

What I do to make vibrations is to put 3 lower screws and tap them with the finger in the corners.
I know it's very unorthodox, but when there are a few sectors left to read and I know it's not a scratch on the plate I do it and I get good results.

Must take into account:
1. It is a process that can damage the HDD.
2. I do it when I no longer have access to those few remaining sectors.

From a technological design perspective, the "tapping technique" does not make much sense in theory.
If this method was perceived to have worked on a Toshiba laptop HDD, which I vaguely believe you may have posted about on the forum somewhat recently, it worked more than likely because the bad sectors have "become healthy, therefore readable" due to an "inner ECC method" existent on some Toshiba drives.

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 Post subject: Re: Deformation of dishes?
PostPosted: December 6th, 2018, 14:44 
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FYI, the TOSHIBA MK8034GSX SMART report includes a "Disk Shift" attribute.

According to the following web page, Disk Shift is the "distance the disk has shifted relative to the spindle (usually due to shock or temperature). Unit of measure is unknown."

http://en.wikipedia.org/wiki/S.M.A.R.T.

The fact that the drive can measure its own disk shift (RRO) would suggest that it should be able to recalibrate its track servo to account for it.

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 Post subject: Re: Deformation of dishes?
PostPosted: December 6th, 2018, 16:43 
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I'm testing it continuously with this 2.0 TB WD, and I'm sure it's because of the vibrations. I come as soon as I stop giving vibrations stop reading well and leave many sectors unread and if I give it vibrations it reads it almost 100% and what it does not read in the next pass reads it to me if I give it vibrations.
mhp666 wrote:
From a technological design perspective, the "tapping technique" does not make much sense in theory.
If this method was perceived to have worked on a Toshiba laptop HDD, which I vaguely believe you may have posted about on the forum somewhat recently, it worked more than likely because the bad sectors have "become healthy, therefore readable" due to an "inner ECC method" existent on some Toshiba drives.

I remember the case you told me and that thanks to the vibrations I made an exact copy of the HDD.

Or it is because of the eccentricity or it could be that the heads take with the vibrations an optimal distance to the plate. For the moment I am leaning towards eccentricity.
Until I discover another method to gain access to these sectors that I can not read, I will continue using this method, although I do not like anything.

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 Post subject: Re: Deformation of dishes?
PostPosted: December 6th, 2018, 16:52 
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Does the WD PCB have 3 shock sensors or just the one? What is the PCB part number?

Does the drive have a dual stage actuator? What is the model number?

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 Post subject: Re: Deformation of dishes?
PostPosted: December 6th, 2018, 16:59 
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fzabkar wrote:
Does the WD PCB have 3 shock sensors or just the one? What is the PCB part number?

pcb : 2060-771960-000 REV. A
fzabkar wrote:
Does the drive have a dual stage actuator? What is the model number?

THE HDD is a WD20NMVW-11AV3S0, I do not know what a double stage actuator is. I have not opened the HDD.

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 Post subject: Re: Deformation of dishes?
PostPosted: December 6th, 2018, 17:12 
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https://sep.yimg.com/ay/yhst-14437584971410/91710951-6.gif

There are two shock sensors at the top left (SK4) and bottom right (SK3) corners of the above PCB, so it would appear that the drive supports Vibration Control Technology (VCT) or RAFF. I confess that I don't understand the difference, assuming there is any.

Since you appear to be in the mood for experimentation, it might be interesting to see how the drive responds to induced vibrations in the absence of one or both of these sensors. You might also like to test the drive's behaviour in the presence of a regular vibration, eg an electric toothbrush or shaver. :-)

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 Post subject: Re: Deformation of dishes?
PostPosted: December 6th, 2018, 17:25 
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fzabkar wrote:
Since you appear to be in the mood for experimentation, it might be interesting to see how the drive responds to induced vibrations in the absence of one or both of these sensors. You might also like to test the drive's behaviour in the presence of a regular vibration, eg an electric toothbrush or shaver.

I'm going to try it this weekend and I'll comment on the results.
Like I make a base with an unbalanced fan to produce vibrations and so I can control the vibrations easily.

Greetings.

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 Post subject: Re: Deformation of dishes?
PostPosted: December 9th, 2018, 16:28 
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In the end I made a vibrating table with a fan with a single blade.

In the end in one of the blows the heads have stuck to the plates (as expected, that or something worse).

I have asked for some vibrators to make a vibrating base, which I can control in frequency and impact.

If I remove all the impact sensors the HDD is not able to read nor the SA. In total it takes three, if I remove the one next to the engine alone, the HDD reads without problems.

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 Post subject: Re: Deformation of dishes?
PostPosted: December 9th, 2018, 16:59 
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FYI, here is the corresponding circuit from a Samsung HD204UI:

Code:
                    Vref  (bias voltage from
                     +     motor controller)
                     |                               opamps = MC33501
             .-------+                               HDD = Samsung HD204UI
             |       |             VCC
             |     .-+-.            +
             |     |   |            |
             |     |  .-.     .-----+                            abridged
             |    --- | | 2M7 |     |                            circuit #2
            ---   --- | |     |    ---
  shock     ---    |  '-'     |    ---                          .---------.
  sensor #1  |     |   |      |     |                           | amp #2  |
   .---.     |     '-+-'      |    ===           summing        |         |  .---.
   |   |     |       |     3|\|2   GND           junction       |    /|   |  |   |
  _|_  '-----)-------+------|+\ 1         ||   ___     ___   || |   /+|------'  _|_
  XXX        |       amp #1 |  >-------+--||--|___|-+-|___|--||-|--<  |   |     XXX
  -+-  .-----)-------+------|-/5       |  ||        |        || |   \-|------.  -+-
   |   |     |       |     4|/|        |            |           |    \|   |  |   |
   '---'     |       |        |        |            +-------.   |         |  '---'
             |     .-+-.     ===       |            |       |   '---------'  shock
            .-.    |   |     GND       |          .-+-.  .--|---------.      sensor
        15K | |    |  .-.              |          |   |  |  |         |       #2
            | |   --- | | 2M7          |         .-.  |  |  | |\|     |
            '-'   --- | |              |         | | --- |  '-|-\     |
             |     |  '-'     1M       |     2M7 | | --- |    |  >--. |
             |     |   |      ___      |         '-'  |  |   -|+/   | |
             |     '-+-'  .--|___|--.  |          |   |  |    |/|   | |
             |       |    |         |  |          '-+-'  |          | |
             '-------+----+         +--'            |    |  summing | |
                          |   ||    |               |    |   amp    | |
                          '---||----'               '----|----------' |  motor
                              ||                         |            | controller
                                                         '------------'

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 Post subject: Re: Deformation of dishes?
PostPosted: December 9th, 2018, 17:25 
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fzabkar wrote:
Para su información, aquí está el circuito correspondiente de un Samsung HD204UI:

Thanks for the scheme, when I have the base I will continue to test the vibrations theme.
The pity is that I do not have another HDD at this time that has that problem, anyway as I have many hard drives to test, I will submit to any of them to see how they affect these. Personally I am very interested in this topic.

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