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Released June 2009 / 2.66, 2.8, or 3.06 GHz Core 2 Duo Processor

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Is the display backlight driver on the motherboard or in the display

I have a Macbook Pro mid-2009 15”. My question is this:

Where is the cicuitry that drives the backlight display located? Is it somewhere on the main board (logic board, motherboard), or is it on (or in) the display in the back case?

The background to the problem is as follows:

Basic symptoms:

After the Macboook has been running for about 5 minutes, with the display near full brightness, the backlight suddenly goes off. If I hold a flashlight within a centimetre or so of the display I can see that information is still being displayed on it, but it is exceptionally difficult to read without a backlight.

Operating condition 1)

If I turn on the Macbook and the display is set to about 90% brightness or higher, the display backlight suddenly turns off after about 5 minutes or less. If I turn off the Macbook for about 10 minutes and turn it on again, the display comes on again, but goes off again spontaneously after about 5 minutes.

Operating condition 2)

If I have the display set at a lower brightness, about 75% brightness, the display runs for a little longer, about 10 minutes, before it goes off spontaneously. And if I leave the Macbook turned off for about 10 minutes and turn it on again the display backlight comes on again and the display works properly until the backlight suddenly turns off after about 10 minutes or so.

Operating condition 3)

If I have the display set to about 50% brightness or less, the display runs properly for at least 10-12 hours and the display backlight does NOT turn off.

My conclusions:

I assume that the backlight driver circuitry is overheating and turning itself off temporarily until it cools down. I have encountered similar behaviour in electronic circuits that are near failure). I also assume that it is very expensive to fix the backlight circuit and probably not worth doing for a 2009 Macbook that has a couple of other issues too (broken back-case frame, and dodgy wireless).

If the backlight driver circuit is faulty, and it is located on the motherboard (logic board) I will throw the logic board away and get another one. Or if the backlight circuitry is located on, or in, the display I will throw the display away and replace it.

I have unplugged and reconnected the display cable at the motherboard to make sure it did not have a bad/dirty connection.

I don’t know exactly which motherboard model I have but it has two fans. The serial number printed on the back cover is:       W89365SP7XJ, … BUT …

The serial number reported by the System Profiler is: W89266HL642

The Macbook might have the wrong back cover on it so the System Profiler number is the most trustworthy.

Serial number printed on RAM slots:  W89240CGW6XNA

Can anyone tell me for sure where the driver circuitry for the display backlight is located?

And is my conclusion faulty?

Thank you

Michael Walsh

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The driver logic is on the backside of the logic board its U9701

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I would take some flux placing around the edge of the chip and then shield the area with foil so you can heat the chip to reflow it. See if you can recover the driver Vs replacing the logic board.

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Thanks Dan. I'm not sure if I will be able to do what you suggest because my eyesight is not what it used to be and I have trouble seeing the detail that is necessary to do what you suggest.

It has not always been this way. Back in 1977 I built my first computer, an MK6800, by soldering all the ICs onto a motherboard and a comms board - it had to be programmed in Assembler. I was quite good at building circuits back then. But that was over 40 years ago and degrading eyesight has caught up with me.

However, your information about the location of this circuit is critical in helping me decide what to do with this machine.




Dan, I have just determined that the serial number reported by the System Profiler (About this Mac > More Info ) is W89266HL642 which is different to what was printed on the back cover. Is your answer still correct using this new serial number?

Many thanks


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