Diagnosing laptop backlight problems

Your laptop's backlight is blinking? Or it's completely dark but you can still see the image when you shine a flashlight at the screen?  You need a new inverter or a new backlight.  How do you know which?  

CCFL backlight lamps are typically rated for 50,000 hours but that's only the average life expectancy.  Yours might go out much sooner.  The brightness control adjusts backlight life as well as brightness.  Keeping brightness turned high all the time shortens the backlight's life.  Symptoms of a dying backlight may include:

CCFL lamps draw more current and power as they age.    A failing CCFL can make you think your inverter's bad when the problem is really a bad backlight.   Inverter failure is possible but much less common.

A failing CCFL lamp can cause the inverter to shut down.   Laptop inverters have a safety-shutoff feature.  The inverters have current sensors in them and when the CCFL's current grows too high the inverter shuts itself off for safety.  Some notebooks use two CCFL backlights and an inverter with dual outputs.  If either CCFL is bad the whole inverter will shut down and even the remaining good CCFL will stay dark. This leads you to think that the inverter is the culprit when it's really a bad CCFL.  Putting in a new inverter won't solve anything. It will just waste your time and money.

You need to test your laptop's backlight with a known good inverter AND, independently, test your laptop's inverter with a known good backlight.  It's easier than you might think. Here's how:

I use an aftermarket dual CCFL product that gamers buy to light up the insides of their computer cases.  This is a perfect source of two, known-good, test CCFLs and a known-good test inverter with dual outputs.  Mine runs on 12V power that any desktop computer puts out.  It came with a switch to turn it off and on....very helpful!  And it was cheap! 

I cut the CCFL's wires halfway between the new test inverter and the test CCFLs.  This leaves me with enough wire length to connect the test inverter to the laptop's backlights, and also enough wire to connect my test CCFLs to the laptop's inverter.

But now you say, "The connectors are missing!  How do you connect the cut wires to the connectors?"  Well, the cut wires from the test CCFLs can usually be jammed onto the inverter's output pins.  The pins are small and sharp enough that, with care, they'll penetrate the stub end of the wire and connect with the insulated conductor.  Be careful!  Don't bend the inverter's output pins.  Now I've connected my test CCFLs to the laptop's inverter.  I turn on the laptop. If the test CCFLs light up then the laptop's inverter is OK!

The test inverter's outputs are now cut wires too.   I stripped off about 4mm of insulation from each wire.  Then I separated the stranded conductors and cut out about half of the strands and tightly twisted the remaining strands.  This made a pointy stub, small enough to poke into the hole of the laptop's backlight connector.  There was enough friction to keep the connections from falling apart.  Now I can test the laptop's CCFLs with the test inverter.  Now, the test inverter is perhaps strong enough and stupid enough (it lacks the safety shutoff feature) so it forces a laptop's dying CCFL light up, but look carefully......is it as bright as it should be?  If the laptop has two CCFLs, is one of them dimmer than the other?  If so, this tells me that the dim one is failing and the laptop's inverter may detect this and shut itself down to protect itself.

You could still have a third problem with the video controller in your laptop, which is responsible for telling the inverter to turn on.  If the video controller has failed then you have a problem which this guide hasn't addressed.  You'll need to get a connection diagram for the inverter's input connector and measure the signal from the video controller to see if the inverter is really being told to turn on.  Fortunately, this type of failure is much less common.

Hope this helps!
P.S.  Replacing the backlight is a laborious and painstaking process.  TFT LCD panels are not designed to facilitate the replacement process.  The CCFL tubes themselves are cheap, $10-$12.  I've done it 4 times now, all successful, but enough to convince me that it is not economical if a customer is paying for the labor.  At this point I would only attempt it if it were for myself, for my wife, or for a very good friend.  And there is considerable risk that the TFT LCD panel will be damaged in the process.  Better to find a good used LCD panel on eBay.