Inverter or Backlight... how to tell?

[kisk]

Just like the topic title... how do you rule out whether its the inverter or backlight that has gone out.

 

[anonymous Mac Tech]

Swapping parts unless you have some sort of homemade backlight tester.

 

[mraikes]

Here's one way to test the inverter:
http://www.fonerbooks.com/test.htm

It works pretty well, and with a good enough multimeter you don't even have to disassemble the laptop. But it does take a little practice.

 

[meanderer]

right now on my desk I have a laptop that has the CCFL off, shine a flash light and you see image
I took it apart and plug the CCFL into my own inverter, it lights up in good color.
I assume the inverter is bad. But before I got a solid conclusion I boot my laptop up. and press the lid button (it was a compaq R3000, the button sticks out in a obvious way). When I release the lid button, the light flashes for a split second then goes off.

It is possible that the lid button is bad so it assume the light should be off when in fact it should be on. But I then hold the lid button, the computer goes into standby and the screen fades out. If the lid button was bad it would've been suspending all the time. By this reason I ruled it out and conclude that it is the inverter.

It is also very possible that the CCFL is bad, causing the inverter to invoke protection and shut itself down. However, looking at the CCFL I had when connected to my own working inverter, the coloration and brightness doesn't indicate such.

 

[ATTech]

Shining a flashlight onto the screen isn't going to tell you whether it's the inverter of backlight, it will tell you if it's a POST/GPU/Screen problem Vs. an Inverter/Backlight problem, but the same can be achieved by hooking it up to an external monitor.

Use the method posted above with the Multimeter; it works quite well.

 

[atlanticjim]

Shining a flashlight onto the screen isn't going to tell you whether it's the inverter of backlight, it will tell you if it's a POST/GPU/Screen problem Vs. an Inverter/Backlight problem, but the same can be achieved by hooking it up to an external monitor.

Use the method posted above with the Multimeter; it works quite well.

You gave this answer before I could. Remember what each part does. GPU = data to the screen. Inverter = power to the backlight.

 

[anonymous Mac Tech]

1. get a flash light
2. turn of the lights
3. power on the laptop
4. shine your flashlight into the screen if you see text, logos etc change the inverter

Most of the time it is the inverter as the backlight has I believe 50,000 hours of life.

In my experience if the screen comes on for a split sec than gradually disappears its the backlight but that usually rare.

I can tell you don't run into this very often. Also in my experience you are completely bass ackwards on your analogy of the screen coming on and going off. In my experience that is most likely to be the inverter (but I still would never say one or the other without swapping to be sure). But still there really is no guessing or definite symptom of which is which. Being a tech a lot of times is swapping parts until it works. Many times just keeping a busted LCD around with a known good ccfl tube to plug in is good enough to be 90-95% sure anyway.

 

[meanderer]

Shining a flashlight onto the screen isn't going to tell you whether it's the inverter of backlight, it will tell you if it's a POST/GPU/Screen problem Vs. an Inverter/Backlight problem, but the same can be achieved by hooking it up to an external monitor.

Use the method posted above with the Multimeter; it works quite well.

can you share the multimeter method?

 

[Pc Fixed Right]

yes the backwards method is good when you don't use the multimeter method. The external monitor trick also works if there is infact a post issue. The OP only asked about inverter/backlight issues not posting issues. I have only changed out 1 backlight in the last 6 years but numerous inverters =P without the use of a multimeter.

 

[ATTech]

can you share the multimeter method?

See the second reply in this thread for the Link.

yes the backwards method is good when you don't use the multimeter method. The external monitor trick also works if there is infact a post issue. The OP only asked about inverter/backlight issues not posting issues. I have only changed out 1 backlight in the last 6 years but numerous inverters =P without the use of a multimeter.

Again, if you've narrowed it down to Backlight vs Inverter, shining a flashlight into the screen WILL NOT tell you which is the problem.