Here are instructions for replacing screen inverter in IBM ThinkPad T40, T40p, T41, T41p, T42, T42p series laptops. All these models are identical and share the same disassembly steps.

What is the screen inverter in a laptop computer? Why would you want to replace the inverter?

The screen inverter is a small circuit board witch is located inside the laptop display panel, you’ll find it below the LCD screen. The screen inverter provides high voltage AC power for the backlight bulb (CCFL) and because of that the image on the screen is bright. If the inverter board fails, the LCD screen remains dark after the laptop is turned on and the image on the screen is very dark, almost invisible. You still should see the image on the screen under a bright light but without backlight the laptop is unusable.

How to fix this problem? Disassemble the display panel and replace the inverter.
Will it fix your problem? Most likely yes.
Why did I say most likely? Because this problem also can be related to the backlight bulb witch is located inside the LCD screen. If you have a faulty backlight bulb, replacing the inverter board will not fix the problem. You’ll have to replace the LCD screen or the backlight bulb inside the LCD screen.

Most common symptoms of a faulty screen inverter:
1. The laptop start as usual but after some times the screen goes black. The image is still on the screen but it’s very dark.
2. The laptop turns on but the LCD screen is dark all the time. The image is still on the screen but it’s very dark. The laptop works fine with an external monitor.

Not sure witch inverter to buy? Find the inverter part number on the page 190 in the service manual.