no display backlight

how can I tell if inverter or inverter cable is bad?

External video works, and I can see display on laptop screen but no backlight...

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It's not always easy to tell. Sometimes (but not always) a bad inverter cable will be evident by moving the display assembly around. If the backlight flickers when you do this, it's the inverter cable. If the backlight is consistently off, the only thing you can really do is swap out one part at a time (inverter, then cables). Ultimately, it could be a larger component (LCD or logic board).

Here's hoping it's an easy fix!

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Good point about "moving the display assembly around". Bassiemike, it would be helpful to know if the backlight is permanently dead, or if there are more details to its behavior. I was assuming permanently dead.

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The inverter cable and the inverter board are not very expensive parts to buy so if you're willing to do the repair my advice would be to order the two parts cause it's really frustrating to swap one with no result and asking yourself why you didn't order the other part too. Most of the time the cable is the culprit but the inverter board or the backlight could also be the problem.

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Unfortunately, I think replacing one or the other is the only way to determine that. However, the cable is more likely the culprit, so I'd say that's a better place to start than the inverter. Actually, the screen itself is often bad in this situation...I hate to say it, but due to the difficulty getting PowerBook screen casings apart, I generally just replace the whole thing if possible -- screen with casing, hinge, and cabling. If you can find one cheap enough on eBay or whatever, you'll likely be saving yourself a lot of trouble and aggravation, although pulling it apart and granularly testing the components is possible.

Also, I'm assuming you can see the image but the backlight is dead. If there is no image at all, testing the external video is the next step. Good luck!

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Had issue with exactly the same problem come through the workshop this week and it turned out to be a bad seated connection on the back of the LCD...

Not something I would recommend as a test in any scenario really but try hitting the right hand side of the screen about halfway up (not with a hammer or blunt object of course), this might sound stupid but if by hitting it you see any flicker in video this might lead to it being a connection problem.

As I am typing this I have just repaired a macbook invetor cable (data) by soldering in a new fine cable on pin one which wasnt giving me a connection with my multimeter.

You gotta remember the invertor is resposible from changing a voltage from like 5V to like 70 thousand volts! Of course there is a very low current! But it's a big task I'm not surprised they conk out eventually especially considering where they live!

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PowerBook G4, Aluminum 15 inch, 1.5 GHz.

LCD backlight not working, keyboard backlight not working (just noticed this)

Have replaced the inverter twice and the small antennae board, no luck.

Suspect the logic board has a problem, have seen something about the VDIM circuit not working, thus the backlight not working, maybe.

Is there something common between power for the LCD backlight and keyboard backlight?

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bassiemike will be eternally grateful.
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