FOR TRAINED LAPTOP TECHNICIANS ONLY:
If you are a laptop technician, chances are you’ve run into situations where you’ve had to determine whether a customer’s LCD backlight was bad or the LCD inverter board was bad. Unless you’ve got really expensive equipment (or already figured out this trick), it can either be trial and error or scavenging a known good CCFL tube to test the customer’s inverter with.
First, remember that this test is for LCD screens that use CCFL tubes (this is not for “LED” screens). Second, remember proper anti-static measures, safety precautions and so on. And finally, remember that an LCD inverter outputs quite a nasty amount of voltage at a very high frequency. If you do not know what you are doing working around electricity, (and are not a laptop technician) do not attempt this. If you ARE a laptop technician who knows how to work with electricity, then try this at your own risk!!!
Here’s what you will need:
- One 12V neon Desktop PC case mod kit (single tube kit should work, double is better)
- One broken or unneeded LCD inverter board
- One 12V DC power supply (any decent 120VAC to 12VDC power supply should work)
- Some electrical tape
- A soldering gun and solder (and the ability to use them)
- A multimeter
Putting together your CCFL backlight tester is very easy. Simply follow these steps:
- The first step is to cut the power leads on the case mod kit. These will be the leads that would normally plug into your PC’s power supply (usually into an unused hard drive/optical drive power connector).
- Next, cut the end off your 12VDC power supply. Use the multimeter to determine which wire is positive (or you can use the markings on the wires, but I’ve found them not always accurate).
- Wire the positive wire from the DC adapter to the positive wire from the neon case mod kit (normally, if it’s properly color coded, it will be yellow). Tape the wires together.
- Wire the negative wire from the DC adapter to the negative wire from the neon case mod kit (normally, if it’s properly color coded, it will be black). Tape the wires together.
- Desolder the CCFL power connector from your broken/unneeded laptop inverter board.
- Cut off one of the neon case mod tubes leaving some wire on both the plug end and the neon tube end (just in case you decide to reuse the tube).
- Solder the wires coming out of the case mod inverter to the CCFL power connector.
- Tape up your new CCFL test socket (again, remember there will be high voltage coming out of it).
Optionally, you can install a switch between your 12VDC adapter and your case mod inverter.
Anyway, that’s it! You now have a laptop CCFL backlight tester!!! The next time you get in a laptop that you know has either a bad inverter board or a bad CCFL tube, simply open up the screen bezel, unplug the CCFL tube from the laptop’s inverter, plug the CCFL tube into your tester, and turn the tester on! The CCFL tube should light up – or not, if it’s bad.
Here’s a video of our little test unit in use. The tester isn’t pretty yet, but it’s just something we threw together on the fly to retest a customer’s CCFL (turned out our initial diagnosis of a bad inverter was correct, and the brand new replacement inverter is also bad).
Apologies for the video quality. It was shot with a T-Mobile G1 (crappy video quality), one handed, while demonstrating the testing with the other hand.