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Laptop backlight won't turn on sometimes (Asus F8SP)

By Karmashock ยท 7 replies
Jan 22, 2009
  1. Sometimes the backlight won't turn on in the laptop. I don't think it's a connection issue. Sometimes either the laptop's hardware or the video card is just not turning the backlight on. I can see that the display is on by the way... just so faint as to not be recognizable unless in the sun or a flash light is shined on the screen.

    I've come to this conclusion because the only way to fix the issue when it happens is to plug an external monitor into the laptop, set it as the primary display, and then reboot. The laptop backlight then comes on and will work find if I disconnect the external monitor. The backlight only seems to go off sometime immediately after boot. That is WHILE the laptop is posting. It shows the American trends bios screen for about 1 second and then the backlight turns off.

    I've called Asus about this a few times and they always start by talking about an "electrical reset" which apparently accomplished on this unit by leaving the battery out for 10 minutes and then booting the machine with ONLY the battery connected. This has frequently caused the backlight to stay on a half second longer but beyond that no result.

    Anyone have an idea about this thing? It's very frustrating because it makes the laptop less mobile. It means that at any time on the road it could be almost entirely unusable... since the only way to fix it is to plug an external monitor into it.
  2. Karmashock

    Karmashock TS Rookie Topic Starter Posts: 223

    they're pretty clueless...

    Every time I talk to them they ask me my model number and serial number... then ask me to do things that aren't possible on this model laptop... I explain that... and then they say "oh, F8's must not have that feature"... Which begs the question of why I bother telling them the model if they're not going to give me model specific tech support?

    The problem is weird... I think there's a circuit board that isn't part of the motherboard or video card that's screwed up. I don't mind the problem so long as there's a quick way to fix it on the go that doesn't require a spare monitor.
  3. pyromaster114

    pyromaster114 TS Guru Posts: 243

    From my experience with most laptop hardware, the backlight is usually governed by the little inverter board that powers it.
    The backlight needs a higher voltage from what I understand, so there's a small circuit board, usually located right under the display panel itself, that raises the voltage from what the battery is putting out.
    This circuit board usually also has a self-test feature. If it detects something it thinks isn't quite right, it shuts it off the power to the backlight. This circuit, or something in the backlight itself, could be malfunctioning, and triggering the safety shutoff on the board.

    Now, I'm not familiar with your model, but from the description of the problem, it sounds like a problem related to this.

    It also could possibly be a short in the switch that is involved with turning off the backlight when you shut the laptop. It definitely sounds like a hardware malfunction though, so it's most likely something that will require new parts.

    I don't think the video card actually has much to do with the backlight, as it's job is just to render the image and put it out to the screen. It's also very odd that plugging in the external monitor fixes it. That shouldn't have anything to do with turning on the backlight really... it's almost as if your laptop's BIOS is messed up.
    Have you tried resetting it? (There should be a 'reset to factory defaults' option somewhere in the settings... try that and see. If not, I'm out of ideas that don't involve hardware replacements.)

    Does the laptop give you any error during the POST?
    If there is a hardware problem (which it does seem like there would be...) I'd check the inverter board first. (Can't think of a way to really test it though, less you happen to have a spare one and could install it and check.)
  4. Karmashock

    Karmashock TS Rookie Topic Starter Posts: 223

    I've taken apart a few laptops and have seen similar boards. It was my guess as well that it was the problem.

    I'd like not to have to send it back to them if possible... This is what I hate about laptops... impossible just to maintain on your own. :(

    I've reset the bios a few times. That has no effect. Leaving the battery out which doesn't reset the bios has more of an effect... though only for about 1 second.

    Well, what I was thinking is that the laptop can turn the monitor OFF when you shift to an external display.

    Somehow turning the monitor off and then rebooting the laptop seems to fix it. When the laptop reboots the laptop monitor turns right on backlight and all... and stays on. It does sound like there is something wrong with the inverter... or some other related component But so far the issue is ALMOST managable.

    I'm really looking for a way to fix it on the go. Perhaps a way to change monitor settings, auto confirm, and then reboot the machine? Does anyone know how to script that? The problem doesn't happen while the machine is being used but AT boot. So if I could map a correction script to a hotkey... that would mean that the worst I'd have to deal with would be a quick reboot after the problem happens.
  5. pyromaster114

    pyromaster114 TS Guru Posts: 243

    Other than hitting the hotkey shortcut for the monitor switch, I don't see any way of trying to change the monitor settings without the external monitor connected... on account of that windows usually won't allow you to enable the external monitor usually unless it confirms that it's connected.

    If the laptop is new, or still under warranty, I recommend that you do send it back to them and get it fixed, cause it sucks having to use workarounds, and such a problem like this could be an indication of further problems.

    If I find anything out I'll let you know, but I seem to be about as clueless as you are at the moment about how to solve this.
    You're saying that the backlight turns off before it even gets to windows... so it still sounds like a hardware problem or problem with the BIOS / CMOS settings... although for some reason you're able to get it to turn on with the external monitor connected, so theoretically the physical hardware is good.
  6. Karmashock

    Karmashock TS Rookie Topic Starter Posts: 223

    a minor update:
    After setting it back to the old settings it's not causing any more problems. There is clearly something wrong with the hardware because if it were just drivers it wouldn't cause problems in the bios. But for whatever reason if I'm careful to keep the primary display ON in ALL configurations there are no problems.

    All I have to avoid disabling the built in display... because it will not always turn back on.
  7. jimjoe

    jimjoe TS Rookie

    got it

    i have had this problem for days now but i just fixed it....
    mine was a ground fault on the graphics card....
    a screw was loose and not making a connection along that screw
    now the continuity of that ciruit which i am guessing was a ground, is working!!!!!1 yeah!
    check the screws in your graphics card maybe you have the same problem ....
    i had a asus w3j.... damn this is bitchin i am so happy its working again...
  8. Karmashock

    Karmashock TS Rookie Topic Starter Posts: 223

    my issue was a bios problem. The work around is to never disable the built in display.
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