Laptop screen: after some time the backlight leds turn off...

keropi

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Hiya!!!

a friend of mine gave me his old laptop, a 1.6ghz centrino/ddr2/intel950 gfx, for free... the catch is that after some 20-30mins, the screen's backlight just turns off , and although gfx are shown, you can't really see anything... a reset or power-cycle fixes that... strange eh?
So I think I will try to fix the screen, the way I figured it (without tech knowledge) is that there is some kind of part that controls the backlight leds, and this thing after some time it gets warm and just shuts off... could be a little cap AFAIK...
So I am thinking about opening the screen to take a look, does that "warm part that fails" theory sounds good?
Any pointers are welcome :D

ps. the laptop is a Fujitsu Siemens Amilo M1450G
 

jvdbossc

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strange, but...

strange, but...

You do not have a clear case, you do not know for sure if it is :

Software problem?
Hardware problem?

Do some tests with other os's like linux (live-cd's) and see if it happens there to while running. (if you do not wan't linux start xp install cd and do not install anything, leave it running)

I had some strange results :blink: with laptops running other os's:blink: It just could be a fault in acpi power management, whatever OS you are running.

The bios is also a suspect. (upgrade) Or somethimes Downgrade..

I know the modern os does not care much for the bios, but if hardware drivers are not done(or installed) properly (incomplete) etc it is still the one who regulates...

If you test it with linux before starting the kernel do acpi=off apm=off
 

imnogeek

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^ What he says as a first stop, it is worth trying on live CD first and there are posts around the web about Fujitsu power saving features causing siimilar effects.

if you still have problems then google amilio backlight and there are a few issues with faulty screen switches - read this one to give you an idea http://forum.ts.fujitsu.com/forum/viewtopic.php?f=98&t=35361

Gary
 

keropi

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I will see the link imnogeek suggested, it is a hardware issue for sure, it happened in the BIOS screen too ... already whiped the HDD and installed XP on top after formatting, it even happened in the last part of the installation...
 

SkydivinGirl

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There's a notebook here at work that does the same exact thing. I even left the machine sitting at the BIOS screen to make sure it was not a problem with Windows. Turn on the machine and it lights up just fine. Wait a little while and the backlight goes out but the LCD is still displaying the image... You just can't see it unless you hold it in a certain direction to get a little light on it.

I replaced the the small power board that is connected to the LCD but still have the same problem. I gave up on it at that point since the computer is old and not worth what it would cost to troubleshoot it further.

I hope you figure it out. Let us know if you do. :)

Heather
 

Merlin

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Have you tried disabling power management in the BIOS?
 

keropi

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sorry, I forgot to update the thread...
I concluded it is the lcd inverter overheating and eventually just shuts down... If the screen does not have it's bezel on, then the inverter gets air, thus it does not shut down easily... if you close the bezel, and put the machine in a cold enviroment it can last 5-6hrs fine... put it back in a heated room and in ~40-60mins you get the lights off...
 

SkydivinGirl

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That's the board I replaced in the one here, the Power Inverter. I did check the power saving settings and they were disabled. Oh well... :)

Heather
 

rkauer

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@Ker: what about you add a very small heatsink to the semiconductors on that tiny board?
 

keropi

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sadly there is no space for that rkauer... I have thought about making some ventilation holes in the bezel , but only if I could not find a replacement part... holes would be.... very... very.... g.... :LOL:

@sdg: yeah, power settings are irrelevant here too, I just guess 90% that it is the inverter overheating, ofcourse it could also be some other part too... I hope not!
 

UberFreak

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I fixed several LCD monitors recently, these are the possible faults for what you describe:

1) Bad caps or bad driver IC in the inverter circuit
2) Bad caps in the power-supply section that is driving the inverter (very common!)
3) Weak lamps in the LCD panel (if there is an inverter, its not LEDs but CFL - Compact Fluorescent Lamp).
Weak lamps require more power to reach the designated light output, which drives both the inverter & PSU harder, which might cause the protection circuit to power it off after awhile.
This problem is also very common!

My suggestion - first of all, check filter capacitors in the psu section driving the inverter.
Check with an in-circuit ESR meter & if possible, remove from circuit & measure their capacitance with the proper meter.
Also, you can take a panel from another laptop & only connect its lamp(s) to the inverter, see if it shows the same problem.
(each lamp has a two-wire connector to the inverter, there is no polarity).

I was able to fix quite a lot of LCD monitors that were given to recycling in this way.
Good luck!

*** Just an important warning: these CFL lamps work on very high voltage!! do NOT handle the inverter or lamps when they are powered on!!
 
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keropi

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thanks for the tips UberFreak , that was my next step: tear up the laptop and look for the caps that power the inverter... (I don't think the inverter is to blame, after all the 2nd new one behaves the same...)
 

SkydivinGirl

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@Keropi

The one I have did the same with a new inverter. I'd love to hear how you fix it. :)

Heather
 

UberFreak

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My bet is weak lamps causing all the trouble.
It could be bad caps due to heat, but this will happen again at some point with new caps, as long as the lamps require more current.

I've experienced it before more than once.
 
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