Laptop Monitor went Dead

[haklesup]

Last week my laptop's monitor went dark. It worked fine a couple weeks ago and just sat on my desk charging in the mean time. Anyway it wouldn't seem to boot so I connected to the external VGA port and I get video there. Next, I tried pressing [Fn]-F10 and the external monitor flickered like it tried to switch back to internal but it always returns to external. I even tried forcing it from BIOS but it too returns to "simultanious" after each reboot.

Clearly there is a fault associated with the built in LCD monitor but I don't know if it is in the video driver output, digital monitor inputs or the power supply to the display. It would be nice to know, it might be repairable.

To wit, I want to hear some ideas for a test procedure to narrow it down. In particular, if I could simply show DC power to the display or CCFL that would be a significant step. Below are two photos of the electrical connections to the monitor. On the left it seems like a DVI type of interface. Not sure if DC supply is in this bundle. On the right are two coax cables. I initially thought they were power but why in a coax wire. Measuring the exposed metal gets me 0V in any direction. Haven't probed the inside conductor yet.

Anyone have a good idea what the two wires on the right are? no guesses, I already did.

[Bigglez]

(Images deleted)

Please limit your images to 600 pixels (or smaller) - larger
PIX distort the forum pages for many of us.

[MrAl]

Hi Hackle,


You probably thought of this already but the light inside the monitor probably uses AC to power it because
they dont want to use DC or the tube gets blackened on one end way too fast. The AC would be some
frequency probably 5kHz to 100kHz and may have an unusual wave shape.
Just to note really.

If push comes to shove you might end up opening the top panel, in which case you might try
shining some light from behind the panel to see if you can light it up manually while the computer
is running and booted up. If you can see the desktop, it's most likely the tube that is bad or
something associated with it like the power supply for it.

Sorry i dont know much about the electronics inside a laptop so i cant say too much more.

[haklesup]

Please limit your images to 600 pixels (or smaller) - larger
PIX distort the forum pages for many of us.

Just as soon as I get my "upload Image to Post" button back. I'll try in the meantime, I was a bit surprised at the size too but it was a pain in the A** to upload, I didn't want to do it over. The main problem with hosting my own pix is that if I ever decide to use that webspace for something else or change ISP, those pix are gone forever from this board.

Front lighting and looking at the pixels with magnification, they didn't appear to be doing anything. I pulled the coax connectors and found 0VDC WRT shield and WRT each other but duh, I didn't look at AC. Maybe tonight.

I would think that if it were just the backlight, the monitor would still switch when I push [Fn]-F10 unless there is a power good signal for the backlight that also needs to be present.

Next step is to pull the display shell (harder to do, might be welded or hard to unfasten clips, it dosen't just pop open when the screws were removed.

If no luck, I will remove the display and mount it on the wall next to my LCD TV and use it as a MultiMedia browser or TV web browser

[Bob Scott]

Please limit your images to 600 pixels (or smaller) - larger
PIX distort the forum pages for many of us.

Bigglez, just use this control. It works for me!

[Bigglez]

Bigglez, just use this control. It works for me!

Easier said than done. At 75% the PIX is now screen width,
but the text is too small to read...

I'll wait for the right-sided version, thanks!

[haklesup]

I opened the display shell, it was trickier than I expected (to not break it) even after I found the screws behind the bumbers at the top.

The two coax wires were of course, the antenna for the WiFi. Easily confirmed when they were removed and the WiFi signal level dropped from 5 bars(full strength) to 1 bar and the router is only 3 feet away. Duh, I should have got that.

The display had a long thin PCB next to it with the CCFL power supply on it. Its input has ground, +20V and three other pins, one of which has 5V on it. Not sure what these are yet, need to reverse engineer the CCFL P/S to know. Could be Enable input and power good output or something like that. Power is getting to the board but I didn't measure the output. I need a better guess as to the voltage before I blow out my DMM if its too high (750VAC, 1kVDC max). Any Comments?

[Janitor Tzap]

Hi Hackles,

I've taken a part several Laptops that have had dead LCD's.

I would start at the cabling.
These see a lot of mechanical stress.
Thus, the wiring can pull lose from the sockets on the back of the LCD screen.

If by re-seating the wiring connectors restores the screen.
Take some hot glue to the cabling, and glue them down, so they don't pull loose again.
Other than that, check the solder joint's on the connector, and connectors to the back light inverter.


Signed: Janitor Tzap

[Externet]

Shining a flashlight very close range against the front of the screen is the first step; does not need to be from its back. If you see faint signs of desktop images, the trouble is the backlight or its driving circuit.

Miguel

[haklesup]

Shining a flashlight very close range against the front of the screen is the first step; does not need to be from its back. If you see faint signs of desktop images, the trouble is the backlight or its driving circuit.

I tried that before I took it apart, I saw nothing to indicate activity. I didn't expect any either since pressing [Fn]F10 should have been able to turn off the external VGA and stay that way. It always switches back to external, indicating the hardware knows the internal VGA port is bad and therefor never enables the backlight.

I looked up the chip (datasheet) on the CCFL P/S, I should be able to enable it manually and light the display without video if I am lucky. That would indicate the display may be good but video chip in the PC is broken. Can't proove it unless I can determine the wiring to the display and make my own VGA or DVI adapter cable.

[Janitor Tzap]

haklesup,

Since your getting video by connecting an external monitor to the laptop.
That indicates that the on-board video card is working.

I would concentrate on the LCD Monitor of the Laptop.
Checking the wiring first.
Then the voltages on the LCD monitor.
Or the voltages coming from the main body of the laptop to the LCD monitor.

If voltages are missing start back tracking, following back it to voltage regulators.


Signed:Janitor Tzap

[jayson2009]

Laptop still boots up as you can faintly see monitor working. First up I connected an ordinary monitor, booted to the XP boot up window and then nothing. I did a system restore and it then booted up no problems.



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