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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.
If you find this article useful, please consider making a donation to the author. Thank you!
May 31st, 2009 at 3:50 pm
Chris,
Maybe there is a problem with the power socket (DC-IN jack) and the laptop switches from the AC mode to battery mode? Can you reproduce the problem if you wiggle the power adapter tip inside the power socket?
Could be the backlight lamp failure.
Could be connection related problem. Maybe the LCD cable is not making good connection with the screen or inverter. Try reconnecting the cable.
May 31st, 2009 at 3:02 pm
Howdy,
I am having an issue with my HP DV6000 screen. At times the brightness will decrease on it’s own. Sometimes the brighness changes so quickly the screen appears to be blinking. It will then stop and stay darker than the brightness setting. At other times the left side of the screen will be darker than the right. Adjusting the brightness does not help. I have found that physically moving the screen will sometimes fix the problem and the brightness will return to 100%. Any ideas? Thanks
May 24th, 2009 at 10:04 pm
vinay,
Sounds like a problem with the LCD screen and I’ve seen it before many time. Unfortunately, you cannot fix this problem. You’ll have to replace the LCD screen.
May 24th, 2009 at 8:07 pm
hi
laptop tech, plz help with my display screen, plz give some solutions.
as my laptop screen works good but one part of the screen on the right hand side
does nt works like 80% of the screen working & 20% of the screen will be blank
if i press on right side of the screen with my fingers firmly it works if i leave,
it goes blank again is this can be corrected plz help me what can i do for these
May 12th, 2009 at 9:14 am
Hi Laptop Tech,
Thanks for the reply, i have checked out the close lid button and it all seems ok,
also since last time, i sent back the new inverter incase it was faulty, and got a new one..
but there is still no joy
ive tried the old screen and new screen with the new inverter, and its still the dark and barly readable screen.
Is there anything else you can think of?
is it possible it could be a software issue??
Thanks,
Kieran
April 19th, 2009 at 11:57 pm
Kieran,
Did you try the new inverter with the old screen?
Also, if you have the lid close button, make sure the button move freely. If the button is dirty, it might stuck inside the case and the laptop “thinks” the display is closed. As a result it cuts off power from the inverter.
April 17th, 2009 at 2:11 am
Hi there,
I am having a bit of a problem with my laptop, first off i could bearly see the screen, so took it it was the backlight, so bought a new screen,
now still have the same problem with new scree, so went and bought an inverter, but yet again same problem even with a new screen and inverter… totally lost here now, can you think of what it could be? thank you so much
April 12th, 2009 at 8:25 pm
alvin,
It’s hard to tell what’s going on. I assume as you can hear Windows booting, the motherboard is working properly.
I think your problem could be related to the video cable or LCD screen.
April 12th, 2009 at 8:23 pm
Michael,
First of all, you’ll have to find out if the laptop works with an external monitor when the internal screen fails. If the external video works fine, even though there is no image on the internal screen, your problem could be related to the LCD screen or video cable.
April 9th, 2009 at 9:12 pm
my hp pav dv6000 laptop screen is not functioning well anymore.,sometimes when i turn it on, the screen is blank or black..but only the screen coz i can hear windows op is doing its usual stuf until the password screen..since i cant see anything,i hv to press the power button to turn it off to restart..its not the brightness and contrast button i test dat already….sometimes there is light in the lcd lamps but no image..i have to connect it to my desktop monitor to see watz going on..im afraid i might corrupt my harddsk if this problem goes on…help anyone..peace out
March 16th, 2009 at 10:23 pm
I have a VAIO PCG-K33F with a problem I can’t seem to figure out, and I need help please. This laptop turns on and at first and sometimes, I get image and everything, then after a while, I restart the machine and the VAIO intro screen doesn’t appear but I can hear the system going into windows and initialize, there is light in the LCD lamps but there is no WINDOWS IMAGE coming on, can anyone here tell me what the problem might be? thank you so much
March 7th, 2009 at 1:04 pm
James,
Does it work like that right from the start up? When you turn on the laptop, the Compaq logo appears on the screen. Is it in the center of the screen or in the center of the left half of the screen?
I’m just trying to find out if the video works fine in the BIOS and the problem appears only when Windows loads.
March 6th, 2009 at 7:36 am
My Compaq presario v2000 displays the image in only the left half of the screen, while the right half is completely blank. Haven’t checked with the external monitor though. I suppose its the hinge wiring problem, just a guess. Its not that half the screen content is not displayed. Just that the complete content is displayed in the half portion.
Any idea on this problem?
Steve, did u get it fixed??
February 22nd, 2009 at 8:13 pm
MY COMPAQ PRESARIO V5000 LCD SCREEN SHOWS THE DESKTOP IN TRIPLICATE ON THE SCREEN ABOUT 1/3RD FROM THE LEFT THEN A 2 INCH BLACK STRIP TOP TO BOTTOM THEN STARTS OVER AGAIN. EVERYTHING WORKS FINE ON AN EXTERNAL MONITOR. I CAN USE THE LAPTOP IN THIS CONDITION BUT IT IS HARD TO READ THIS WAY.
IS IT THE SCREEN, INVERTER. VIDEO CARD??
January 20th, 2009 at 10:36 pm
RobMac,
Sounds like a problem with the LCD screen.
When the laptop LCD fails and starts displaying lines, can you force it back to normal if you move/twist/torque the display panel. If you can, probably it’s a bad LCD.
January 19th, 2009 at 8:05 pm
Laptop Tech,
What a great site – but I too have a laptop video problem.
On my Acer LT (3230) LCD I get good video then it fails to vertical lines (I can see video changing in lines) then back to a good picture until it once again fails to vertical lines. At first I thought it was heat related but now unsure. Video is stable on an external (VGA) monitor. I have pulled pushed tapped and poked all cables and reset connectors without resolve. Your council would be very welcome.
Regards RobMac.
January 16th, 2009 at 12:59 am
Thanks for clearing that up… I’ve been working on it for days.
January 15th, 2009 at 10:44 pm
Dominick,
It sounds that you still can see the image on the screen, so you problem is not related to the backlight lamp or inverter board.
From your description I can tell that you have a problem with the LCD screen. You’ll have to either replace the screen or use it as is.
January 15th, 2009 at 10:23 pm
Hello, I have an old dell latitude c640 that runs really well, but the screen has a vertical dark patch coming from the bottom-middle of my screen. It is darkest at that spot and changing the screen brightness works every were except that spot. Is this a backlight or inverter problem? I would attempt to use a voltmeter, but I don’t have one and it would cost just as much to buy one than it would buying another inverter.
January 5th, 2009 at 12:54 pm
: ) Thanks ya, i’ll do just that. Right now the CCFL tube is working properly—although it hasn’t for quite some time (over a year, really). Either it’s at its best state, but failing, or it was a wiring issue all along (irony~~). I’m going to try and see how it works placed back in the LCD this time around, but i’ll still order a new one just to be safe.
Just wish it would’ve been working like this in the first place, but my luck permits things like this happening. : D
Thanks for your help, and for the link to the CCFL buy. : ) Really appreciate it!
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?