How to test laptop screen inverter with a multimeter
Is it possible to test laptop screen inverters with a regular multimeter? I was asking myself exactly the same question many times before until I found this article published by Morris Rosenthal. Apparently, you can test inverters with a multimeter but you have to have the right one, with frequency rated at least 50KHz.
my $20 meter failed to register anything! So I borrowed a better meter from my neighbor, a Fluke 110 true RMS meter. The Fluke specs show it’s rated to 50KHz, which turned out to be critical in the inverter test application.
I’m not sure how accurate this test is, so I will probably find a Fluke multimeter and try it myself. If this test works 100%, it will be very helpful to me.
By the way, some of you may ask what a screen inverter is and where it’s located inside a laptop? I’ll try to answer in a few words. The inverter board is a power supply for the LCD screen and it powers up the backlight lamp (CCFL) inside the LCD screen. When inverter fails, the LCD screen remains dark even after your turn on the laptop. You still can use the laptop with an external monitor attached to the VGA port but not with the internal screen. The image on the laptop screen will be very dark, almost invisible. The inverter board is located inside the display panel and in most laptops you’ll find the inverter board located right below the LCD screen.
The image below explains how the inverter board is connected to other components inside your laptop. You’ll find more information in this article.
Topics: Video problems, Screen problems, LCD screen, Backlight, Screen inverter |
October 2nd, 2008 at 2:45 pm
my hp screen is half dark, still workable but 50% darker than new. Is it backlight or inverter problem?
October 2nd, 2008 at 9:56 pm
Kris Kozlowski,
If the screen is still workable, most likely there is nothing wrong with the backlight or inverter. Probably you’ll have to adjust the screen brightness settings.
On some laptops you can change brightness using shortcut keys on the keyboard. Here are some examples.
IBM ThinkPad. Use Fn+Home (to increase) and Fn+End keys (to decrease).
Toshiba. Use Fn+F6, Fn+F7.
HP Pavilion. Fn+F7, Fn+F8.
November 1st, 2008 at 11:48 am
Kris,
Do you have a large laptop? (Screen size). It is possible that your screen uses TWO backlights, and one is bad.
Robert
November 7th, 2008 at 11:14 am
I can see in my LCD screen the back Light, but can’t see any image.. This is a trouble with the Flex Video Card??
November 7th, 2008 at 11:24 am
Lein,
You’ll have to test your laptop with an external monitor. If there is no video on the external monitor, probably it’s bad video card.
If the external monitor works fine, that’s could be:
1. Loose connection between the video cable and video card (motherboard). Try reconnecting the cable.
2. Bad video cable.
3. Bad LCD screen.
4. Video card (motherboard) problem.
November 10th, 2008 at 4:50 am
Hi, thanks again for such an informative site!
If you have a moment for advice, I would greatly appreciate it. My Acer aspire 5100 has had intermittent days when it starts up but with no display at all. Now its looking like its gone permanently. I tested it on an external monitor and all is fine there. System is working ok.
Had it into acer to repair the issue under warranty 6 mnths back, and they replaced the mainboard, but didnt solve the problem.
Im suspecting the inverter, and am happy to replace it but Im confused since I frequently hear that without the inverter/backlight, I should still be able to see a very faint image on the screen. I cannot. When Im in the system on an external monitor, it doesnt show the ‘default monitor’ as being active, as if its disconnected. Should I be looking at the display cable into the board (twisting damage etc) and if so, how do I get in there (above or below)?
Also, does the intermittent nature of the problem sound like the inverter or cabling? Used to be most common after travel (especially by air)
Many thanks in advance!
November 10th, 2008 at 8:34 am
Topher,
That’s right. When inverter board goes bad it stops powering up the backlight lamp but the data signal still coming to the LCD screen.
Could be:
1. Loose connection between the video cable and LCD screen. Try reconnecting the cable.
2. Defective video cable. Try replacing the cable.
3. Defective LCD screen. You’ll have to replace the LCD screen.
Here are instructions for taking apart the display assembly on an Acer Aspire 5100 laptop.