Diagnosing LCD fault

[Astral]

I bought an LCD monitor yesterday second hand that when plugged into both my SAM and PC laptop, will display a bright picture for about 1-2 seconds before all the brightness goes away. The image is still in the background VERY faintly.

I then found another LCD display in a roadside rubbish dump that displays the same symptoms.

I have never used an LCD monitor before. After playing with settings (what I can see with a near black picture) I believe the monitors to be faulty. Is it likely to be an easy fix for them? Is this a common fault for LCD monitors? I don't wish to get too involved, as I'll just chuck them if it's too much hassle.

[spirantho]

I don't know about TFT screens but I know on laptops they use a power inverter circuit to power the back light which often goes kaput. You might want to scout around and see if you can find one (eBay probably your best bet). You might just get 2 working LCD monitors for very little!

[Stedy]

Hi,

Farnell (http://www.farnell.com) stock a range of CCFL Backlight Inverter modules for LCD panels.
Be warned, these inverters output upto 2000V.
Normally the connection to the Cold Cathode FLuorescent (CCFL) lamps uses a common plug and pinout so you should be able to interchange easily.

You need to look in the back of the monitor and see how the connectors are arranged, some boards have the two outputs at the top and bottom of the PCB, others have them in one place.

The inverter boards also have a low voltage interface that supplied power and a brightness control. Search for any information on your existing panel/inverter to locate a pinout. Then compare the pinout and connector type with the new candidate part.

Good luck.

Ian

[CodePoet]

Hello,

I work at a service centre that repairs Sony LCD TVs and BenQ/Mitsubishi monitors. As others here have stated, it could be an inverter issue - but the problems you're experiencing points more toward a faulty panel (or specifically the CCFL tubes that reside within it)

In cases like yours, one of the CCFL tubes (or the high-tension wiring attached to it) becomes leaky. In the case of the wiring, part of the insulation fails and a corona (or in extreme cases, an ARC) forms around the damaged area and shorts to ground (via the rear of the LCD panel, as it's a grounded shield); The inverter/PSU powers up for two seconds, the display illuminates, but the control/logic realises too much current is being drawn by the inverter circuitry, and shuts down

In most cases it's a write-off, but if you've got the time, you can completely dismantle the panel itself, remove the CCFL tubes, and run them outside of the chasis to see if they remain lit...

Hope this helps!