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Omnibook display, again

Discussion in 'Hardware' started by Tony Moore, Nov 19, 2005.

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  1. Tony Moore

    Tony Moore Thread Starter

    Joined:
    Nov 17, 2005
    Messages:
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    The following concerns an HP Omnibook XE3 GF Notebook, running Windows
    XP Pro.

    Occasionally the screen blanks (completely black) as though the
    machine were in standby mode. This may happen soon after booting or
    after several hour's use. It may happen more than once on one day, or
    maybe it doesn't happen for a couple of weeks.

    After power-switch off, or hardware-reset, to shut down the machine,
    the standby button re-boots it, but the display is _not_ restored.

    However, the display _can_ be restored by: power-switch off, unplug
    the power cord, remove the battery, wait a couple of minutes, replace
    battery and power cord, press standby button to re-boot.

    Having removed/replaced the battery, following a screen blank, Windows
    insists on performing a consistency check on the FAT32 hard drive, at
    next boot. The last time this happened two errors were found:

    Windows will now check the disk.
    Volume Serial Number is 2C77-3ED5
    \WINDOWS\Prefetch\LOGONUI.EXE-0AF22957.pf first allocation unit is
    not valid. The entry will be truncated.
    \WINDOWS\Prefetch\NTOSBOOT-B00DFAAD.pf first allocation unit is
    not valid. The entry will be truncated.
    Convert lost chains to files (Y/N)? Yes
    336 KB in 2 recovered files.
    Windows has made corrections to the file system.

    If the screen did not blank, removing/replacing the battery doesn't
    cause Windows to perform the hard drive check, at next boot.

    I should be grateful for advice as to

    why the screen blanks,

    why Windows performs a consistency check on the hard drive after
    removal and replacement of the battery, following a screen blank,

    how can these problems be fixed,

    what needs to be done about the files listed in the error log?

    Tony
     
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  3. JohnWill

    JohnWill Retired Moderator

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    Well, I'm guessing the two problems are only slightly related. The consistency check is most likely due to killing the power when the machine is in the middle of booting.

    The display blanking sounds like it may be the inverter that powers the back-light getting flaky. Can you see a dim shadow of the displayed data when the screen goes dark?
     
  4. Tony Moore

    Tony Moore Thread Starter

    Joined:
    Nov 17, 2005
    Messages:
    8
    JohnWill wrote

    > Well, I'm guessing the two problems are only slightly related. The
    > consistency check is most likely due to killing the power when the
    > machine is in the middle of booting.

    The consistency check occurs _only_ after the display has blanked. At
    all other times the machine boots normally.

    As far as I know, the power has never been killed during booting.
    Further, when I have used the power-switch or reset button to shut
    down the machine, I have always been careful to wait for the drive
    activity light to extinguish first.

    > The display blanking sounds like it may be the inverter that powers
    > the back-light getting flaky. Can you see a dim shadow of the
    > displayed data when the screen goes dark?

    I understand what you mean by 'dim shadow' because it happened to this
    machine a few months ago. That has been fixed, and hasn't recurred. I
    can use the machine for eight hours and still the screen is bright
    but, when the screen blanks, it is completely black, as though the
    machine were in standby mode.

    When the machine enters standby mode, presumably the video circuitry
    is instructed to interrupt the data flow to the display. Could this
    happen, without pressing the standby button? Is a flag set to indicate
    this condition, and could it be held in volatile memory so that, when
    the battery is removed, the flag is re-set, thus allowing data flow to
    the display again?

    Tony
     
  5. JohnWill

    JohnWill Retired Moderator

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    OK, then the two issues may be related. If the machine completely and suddenly shuts down, it would blank the screen and obviously interrupt any other activity that was happening.

    As far as the details of how standby mode works on the laptop, I can't really say. This does sound like the machine is shutting down totally, I think I'll change my guess to the on-board P/S that is driven from the battery to produce the various voltages required.

    Can you predict when the machine will blank the screen, or is it random?
     
  6. Tony Moore

    Tony Moore Thread Starter

    Joined:
    Nov 17, 2005
    Messages:
    8
    JohnWill wrote:

    > OK, then the two issues may be related. If the machine completely
    > and suddenly shuts down, it would blank the screen and obviously
    > interrupt any other activity that was happening.

    True, but when the screen blanks, the machine _doesn't_ shut down.
    Applications continue to run, which is why I take care, when I do shut
    down the machine, that the hard drive activity light is off.

    > As far as the details of how standby mode works on the laptop, I
    > can't really say.

    I'm mystified as to why, after a screen blackout, removing/replacing
    the battery should make any difference to the way in which the machine
    boots, or why this should trigger Windows to chkdsk.

    Clearly removing/replacing the battery has no effect on the BIOS
    settings held in CMOS RAM. However, I wonder if the HP software which
    controls the machine, makes use of volatile RAM, powered from the
    battery, to hold settings relating to standby, etc. When the battery
    is removed/replaced, these are reset, and the screen is turned on.
    Possible, or nonsense?

    > This does sound like the machine is shutting down totally

    No, please see above.

    > I think I'll change my guess to the on-board P/S that is driven from
    > the battery to produce the various voltages required.

    I don't know if the display inverter takes its power direct from the
    battery but, if there was no power to the inverter, certainly there
    would be no displayed image. Could there be an overload cutout in the
    feed to the inverter, which is reset when power is removed?

    > Can you predict when the machine will blank the screen, or is it
    > random?

    Totally unpredictable. Sometimes twice in one day, sometimes I don't
    see it for a couple of weeks. I've no idea how to induce it.

    Tony
     
  7. JohnWill

    JohnWill Retired Moderator

    Joined:
    Oct 19, 2002
    Messages:
    106,418
    I'm at a loss. I'm 90% certain this is a hardware failure, but without actually seeing it, it's pretty hard to say what exactly is happening.

    The fact that it has to do the consistency check of the filesystem still leads me to believe that it's not a normal standby or shutdown. Obviously, you're running the FAT32 filesystem, since NTFS normally doesn't have to do that check after an abnormal shutdown.
     
  8. Tony Moore

    Tony Moore Thread Starter

    Joined:
    Nov 17, 2005
    Messages:
    8
    On 20 Nov 2005, JohnWill wrote:

    > I'm at a loss. I'm 90% certain this is a hardware failure, but
    > without actually seeing it, it's pretty hard to say what exactly is
    > happening.

    I've noticed that page 121 of the HP Reference Guide, contains the
    following advice:

    : Startup problems
    :
    : If the computer doesn't respond when you turn it on
    :
    : [snip]
    :
    : If you get no response, remove the battery and AC adapter, remove
    : any PC cards, and undock the computer. Then plug in the AC adapter,
    : reset the computer using the system-off switch, and turn it on by
    : pressing the standby button.

    From which, it would seem that removing/replacing the battery does
    have some significance.

    Anyway, JohnWill, I think that we should leave it here, since I've
    already taken too much of your time on this problem. When (if!) I find
    the answer, I'll post it back here.

    Many thanks for your prompt responses, which have certainly given me
    much to think about!

    Tony
     
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