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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.
Here’s how you can test the inverter board using a spare backlight lamp.
Basically, you unplug the LCD screen from the inverter and plug in a known good backlight instead. If your test backlight lamp doesn’t light up, most likely there is a problem with the inverter board.
If you plat to test more than one LCD screen, you mgith consider buying this CCFL bulb and inverter tester designed by LCDParts.net. You can find this tester here.
Finally we have the LCD Screen Tester available (LST01 is including a 12V DC Adapter) after months of experiment with many different types of LCD screens. No more guess works! This custom built equipment can help you isolate problem between CCFL Backlight Lamp and Inverter in seconds.
January 5th, 2009 at 12:19 am
Ash,
Unfortunately, there is no simple answer. You mentioned the screen is reddish when it starts and that sounds like a problem with the backlight.
So, you’ve removed the backlight – the hardest part in the whole repair process. Why wouldn’t you buy a new backlight lamp for test and connect it to the same inverter? You can find a new backlight lamp for less than $10 here, it’s less expensive than a new inverter board.
January 4th, 2009 at 11:05 pm
* furthermore, after typing that last comment, it’s been running longer than ever. I find that only when I fiddle with the shorter pink wire (not the white) on the backlight does the light turn off while plugged into the inverter—but it could even simply be moving the light that causes it to burn out, i’m not sure.
However, now, left untouched it appears to be willing to stay on and white for a good while…that’s the problem, though. I would like to have it safe to move around—the metal around the lamp is pretty hot. Would it be safe to say it was a wiring problem afterall? I know these things are so hard to call on the net, honestly. I really just don’t know what’s faulty here—the technology or my logic. How baffling.
I’m tempted to just hook it back up and see how she’ll run, but i’d like to hear what advice there is for this machine.
–Thanks again!
Ash
January 4th, 2009 at 10:36 pm
Hi there! Hope all’s been well and dandy. I’m thoroughly pleased with the information on this site, as well as :
http://www.laptoprepair101.com/laptop/2007/12/09/replace-laptop-backlight-ccfl-lamp
and:
http://www.fonerbooks.com/laptop14.htm
However! I’m here because I have a question, and I feel confident in your ability to answer.
Here’s what my situation is.
1) I can see faint display on LCD (with no backlight–see #2).
2) CCFL tube turns on with startup, and chooses random points at which to turn off. Although, usually within a matter of minutes, and sometimes seconds. Starts out red (a sign of CCFL tube failure), but warms up to white before turning off.
3)Has no trouble repeating this process over and over. (Starting the light up, and then it turning off within minutes or seconds—I can’t really tell if it’s an inverter problem as it does continually supply power, I suppose it could be though.) I’ve been putting off repairing the display for quite some time, and have tested this many times over the course of a year.
4)I’ve taken out the backlight (boy that was fun) and hooked it directly to the inverter—free from any potential wiring errors. (I’m aware it’s hooked directly to the inverter in the first place XD, but I figured i’d have to do this anyway to replace a part). It still acts the same as if it were still in its original setting. Start up with light, off again soon enough.
5)I have not been able to have the tools to test either or, i’m just hoping you can call it as it is without having to test or order parts.
Is there a way to judge if it’s the CCFL tube or the inverter without testing externally at this point? — If it’s the inverter, would it still supply power to the backlight/get it to turn on?
I know my alternative is to run tests, but can you make a good judgment on it as is?
Hope to hear back from you soon! I’m really looking forward to finally getting this lovely piece of technology functioning at its best. : )
-Thanks for your time!
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.
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 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 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 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
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.
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?