lcd screen not showing desktop but it lights up (dimmed)

Hi,

I am having difficulties with the laptop.

The problem i am facing is: i had a broken screen of my laptop. i recently purchased a new one (of the same model) and installed the screen. however when i power up the laptop, the motherboard lights and everything was working but laptop screen will not show up desktop...it lights up and remains black. i can tell that the screen is ok because there was little light showing but there is nothing else...only dimmed light and that was it.

When i connect the laptop to the external screen via the VGA, everything was showing ok. So i am thinking there is something wrong with the LCD cable.

I wouldnt take the LCD screen because its a brand new one. Also, the motherboard is ok as everything shows up via the external monitor but leaves the internal LCD screen dimmed black.

My only solution here is to get and replace the LCD cable screen which runs from the motherboard to the internal lcd.

Anybody have any inputs.

Please find attached the lcd cable connected to the internal lcd
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BakakaAsked:
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andreasSystem AdminCommented:
Just a dim light from the display does not mean that the display is ok. It could very well be, that the panel will not work due to several problems.

-Panel itself (but unlikely, usually you will see some distorted images or see the damage as its caused by force)
-The panel logic board which addresses and drives the pixel of the panel according to the image to be shown and delivered by the laptop
-The connection cable from Mainboard to screen or the connector on the mainboard.

All you can do is to reseat the cable, optically inspect the sockets and plugs for bend pins loose holding clips, loose soldering points and to wigle the cable around a little bit wilst operating.

Be careful some laptops have the inverter that supplies the CCFL tubes of the backlight on the mainboard so some of the connectors/cables may have a high voltage of round about 1500V.
Quite painful at least if you make accidential contact, and it might fry your laptop if it arcs to somewhere where it soudlnt be.

So dont plug unplug any screen cables when on. dont touch the contacts and solderpoints of the inverter circuit.

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BakakaAuthor Commented:
- panel is brand new.

I am suspecting the connection cable from maiboard to panel.

I have inspected the onboard solder ports of plugs, connected to mainboard, and everything is fine too.  there aren't any loose soldering points from reviewing, and have also reseated the cable connection from mainboard to lcd.

i never do "and to wigle the cable around a little bit wilst operating."

i am aware of these:
Be careful some laptops have the inverter that supplies the CCFL tubes of the backlight on the mainboard so some of the connectors/cables may have a high voltage of round about 1500V.
Quite painful at least if you make accidential contact, and it might fry your laptop if it arcs to somewhere where it soudlnt be.

So dont plug unplug any screen cables when on. dont touch the contacts and solderpoints of the inverter circuit.


if i attempt the option you mention "to wigle the cable around a little bit wilst operating." and nothing comes up, then its gotta be the connection cable from mainboard to lcd.

this is very rear problem as i never come across them.
andreasSystem AdminCommented:
what was the reason that made you think your old panel was defective? Did it cracked or showed strange pixels? Or was ist just black with dim light too?

Maybe the laptop doesnt supply an image at the TFT connector anymore so the panel doesnt get anything to display? So only the external monitor port is still functional.
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BakakaAuthor Commented:
yes, the old panel was cracked. half the side was cracked and the other was ok, but the display is still the same...only dim light too, so i thought it was the panel but after purchasing the new panel, i was able to see all the dim-lights but nothing showing up (ie, desktop, documents, files, etc).

The external monitor port is still functional as i was able to see desktop, documents, files, etc.

its gotta be the cable from mainboard to panel.
andreasSystem AdminCommented:
Could also be the cable, but this should be detectable by wiggling, if image does flicker up when wiggle it its cable (or maybe connector).

Im not sure if all wires of the cable are used, if we assume yes you can use a multimeter to check if all single wires of the cable go thorough.
But if for some reason not all wires are used they may not be connected on one or both sides. is it all a ribbon cable until it goes into the mainboard? Or is is somewhere converted to normal wires when going thorough the hinge into the case of the laptop?
If cable is changing from ribbon to wires on the other end it might be not all wires are going throug or there might be a strange sonncetion (e.g. some wires split up and and up 2 times on the other side, e.g. ground)
BakakaAuthor Commented:
thanks andreas for that. i will check tomorrow and will get back to you. so really the only options are the followings:

(1) wiggle the cable to see if there is anything coming on and off via the screen..if it is then its the cable

(2) then what would it be if the wires of the cable are used and working thorough?
_Commented:
Before you do all that, have you tried toggling the Fn key that swaps between Internal, External, and Both monitors?
It might be 'defaulted' to External. On my laptop, it is Fn+F5

Also check in the BIOS. That might have a setting for which one to use.
BakakaAuthor Commented:
True Coral, I never thought of that. I must try that first too. Will post back once done.
andreasSystem AdminCommented:
But usually when its the Fn trick, the backlight of the TFT isnt on. But it seems its turning on. But of course its well worth a try.
nobusCommented:
it can also be a bad contact in the video connector (onboard)
you said "Also, the motherboard is ok as everything shows up via the external monitor but leaves the internal LCD screen dimmed black.  "  that is not 100% true, it leaves still the video connector, or video chip output that can have a problem
BakakaAuthor Commented:
ok, i think the problems here we can take is,

ill first try and wiggle the connector cable (from mainboard to panel) then if things appears and disappears via the panel then definitely the cable....and if not then

ill test the output from the connector (with multimeter) if all cables are used thorough (both ends, port from mainboard to port lcd connected)...

in this case if the cables are all used, what would it be then or next step then?
andreasSystem AdminCommented:
With multimeter you only can test the cable itself, not the output of the connector a the mainboard. Even you measure something, its not sure if its a valid image signal.

If you cannot surely rule out the calbe as the culprit, I'm afraid you need to change mainboard. Or your new Panel isnt operational (dead on arival).

If you have no 2nd laptop of the same kind, where you can test the panel you cannot find out if its the panel or mainboard. If you cannot get a known good mainboard for cheap, I wouldnt continue to repair the device.

The risk of a 2nd bad buy would be to high for me. Especially as new Notebooks are not that expensive anymore.
BakakaAuthor Commented:
Thanks andreas
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