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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.
March 12th, 2010 at 6:17 pm
Hi there,
My Dell Inspiron 600m laptop was working fine until last week. One day the screen went dim and I could barely see the items on the desktop. I pressed the “logoff” button and it worked fine for 20 mins. So whenever this problem recurred again, I would follow the “logoff” route and work on the laptop. Within 2 days, it started happening more frequently. Now, it barely stays on for a minute after the “logoff” route. I do not see any vertical or horizontal lines on the screen. Its just creating a buzzing sound. When connected to a secondary monitor, I could see everything clearly.
Whats the problem? Inverter or backlight? Please help…
Thanks
July 21st, 2009 at 4:36 pm
I have a suggestion for you on a temporary “snooping” into inverter errors (working/not working) situations. I used an old non-working inverter and put my probes into the high voltage end of the inverter while it was not plugged into anything. I put my Amprobe 33XR-A on ac voltage and on an hp laptop, I read nearly 1 volt of ac. I then switched it over to Hz position and read 54 KHz! So, there! As a former RADAR tech in Uncle Sam’s Air Force, I saved a lot of time to research that! Tear apart an old inverter board and make some probes to plug into the meter and use the mini transformer as a probe or as the ham guys used to call it a grid/dip meter to sniff out RF!
You are welcome!
June 11th, 2009 at 2:33 am
Hi,
Great site, I now have a much better appreciation of my problem. But before I pull apart the wrong things, I thought I’d get an expert opinion… On my fiancee’s Acer travelmate 2420 the backlight fails after a short while (< 1 minute). It can be turned back on with the close lid button but fails soon after (increasingly shorter periods). This only seems to be an issue under AC power. Everything works fine under batteries. Any suggestions?
Thanks
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