LCD backlight is on, but no characters

[GolferJohn]

Hi.

This is with my latitude LM P133

The problem started when I fried the motherboard flashing BIOS A06 (from A11).

I got a new MOBO (actually two) and now the system boots up normally, but the LCD shows no characters, however the backlight is on.(It seems a little dim, but I do not know how bright this should be with no data feed from the CPU).
I bought a new LCD on E-Bay, 'guaranteed' not DOA. I had to take apart the bezel, remove the LCD panel, and flex cable so that I could thread the flex cable through the narrow slot in the upper MOBO case, but I was very careful. NO JOY! the problem remained. I had no problem with flex cables or ZIFF connectors with other components. Are these really tricky with the LCD or?? Using an external monitor, I successfully installed my OS, so it seems to me that the problem lies with the LCD, not with the MOBO, screen memory. Is there any other component on the motherboard specifically for the LCD? Are both LCD panels dead? How likely is it that I killed the LCD panel flashing the BIOS?
Since the system is normal with an external monitor, I cannot see any problem with the MOBO (I have tried both motherboards). Both flex cables appear undamaged. Is it likely that the problem is with the inverter? What is the likelihood both of them are shot? Would the inverter become damaged when a motherboard is fried with a bad BIOS flash?

Any help would be much appreciated.

Thanks,

John

 

[IslandCustom]

Have you tried adjusting contrast? I've seen laptops that are completely blank when the contrast setting is completely down.

 

[GolferJohn]

Thanks, I actually had'nt thought of that, but no joy!
John

 

[IslandCustom]

It's possible that your video output is being directed to the external video connector instead of the LCD. Is there a "function" key on the keyboard that you use to switch between the LCD and an external monitor? My Latitude has one. I believe the key has (in blue printing) two rectangles -- one solid blue and one outlined in blue.

 

[GolferJohn]

yes tried that.
thanks,
John

 

[IslandCustom]

John, I'm runnin' out of ideas here...

 

[micker377]

Have you tried to plug in a standard monitor and switch over? This would tell you if it is the computer or LCD panel.

 

[IslandCustom]

His post said he installed the OS using a standard monitor, so I suppose it's either the LCD itself or a switch/setting somewhere. Do you know of any settings for the LCD in the BIOS?

 

[rclarke250]

Have you tried a new invertor card? most lcd panels are connected to another card to supply other voltages it needs.
But in my experiance this is a an lcd pannel issue.

 

[GolferJohn]

I wonder how likely it would be for both inverter boards (the one on my original LCD, and the one on the 'guaranteed not DOA' panel I purchased on E-Bay) to be bad.
The original was working until I fried the MOBO. Would a bad BIOS flash be likely to kill the inverter board?
The panel I bought was supposedly working, yet it too is blank. I guess I could have been had. I bought a new MOBO from a third party supplier that had been supposedly refurbished by DELL (it was in a DELL box), so the problem should be in the inverter board, or the LCD panel itself.
I guess my next step is to buy a new inverter board.I could get one fairly cheap ($10-15) on E-Bay as well, or elsewhere at considerable higher cost.
Maybe I need to buy a working LM just to use to test parts!!!
I am just looking for some expert advice before I sink any more money into this thing!
Thanks,
John