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 Post subject: Diagnose LCD Inverter
PostPosted: Sun Jan 10, 2010 9:22 pm 
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Joined: Sun Jan 10, 2010 9:10 pm
Posts: 2
Hi,

I'm looking at a friends problem G4 (A1054), have it a bit apart according to the great directions found here, but am wondering how much I should put into it. If it's the inverter, it may be worth me working on it (if the MB, probably not).

The symptom is that when turned on it makes (what I think is) the appropriate sound, and then it looks like the screen tries to come on (a quick light flash on the screen), and then ... nothing. Does that sound like an inverter issue?

Is there any way I can diagnose it further? I think this has a socket to plug in an external monitor... will a system with a bad inverter work when an external display is attached?

If I take the inverter out is there a way to test it (in my repair experience, power devices often go to a short-circuit condition)? Is there a particular component that usually fails on the inverter unit or must I replace the whole thing?

Thanks for any feedback!

- Bri


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 Post subject: Re: Diagnose LCD Inverter
PostPosted: Mon Jan 11, 2010 10:38 am 
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Joined: Thu Feb 27, 2003 6:35 am
Posts: 977
An inverter just controls the backlight. When it goes out, if you look close enough you should still be able to see a picture, but it'd just be like the brightness is turned all the way down. If there is nothing on the screen at all, it is most likely the logic board.


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 Post subject: Re: Diagnose LCD Inverter
PostPosted: Tue Jan 12, 2010 12:58 am 
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Joined: Sun Jan 10, 2010 9:10 pm
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Ah, gotcha. Doesn't seem like an inverter issue then... I do get a flash on the screen at one point, so the lighting seems OK.

When I hit the power button the power cord light goes green, I get the speaker sound and a grunt from the CD drive. Then 5 seconds later the HD spins up and the head is moving, about 4 seconds later is when the LCD flashes. Then I get some more HD activity, 20 seconds after the flash I get more HD activity and the power cord light goes to yellow again. Then I hold the power button for 5 seconds and the HD goes off.

I gather that's all low level hardware stuff, without CPU intervention... anything I can look for on the logic board? I read that some solder joints can get broken.

Thanks!


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 Post subject: Re: Diagnose LCD Inverter
PostPosted: Tue Jan 12, 2010 11:53 am 
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Joined: Thu Feb 27, 2003 6:35 am
Posts: 977
usually on those, the solder on the video chipset gets weak. You can sometimes (although risky) push down on the video chip and it works fine as long as there is pressure. You'll have to be pretty good at soldering to fix it.


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