Early 2011 model, A1278 / 2.3 GHz i5 or 2.7 GHz i7 processor.

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no LCD backlight and no keyboard light

Hi First time posting. Can anyone help with this issue. There is also no video using the external video connector. I have tested the LCD with a flashlight and can see the system booting. I have connected another MBP to the LVID cable and it works fine. I am not sure how to test the backlight fuse marked with a P. should I get 12v on both sides of the fuse when the system is powered on? also, in the picture I point to a round component (330) that is a bit loose and one of the plastic "shields" sides is cracked off. There is not water damage on the system. Thanks Kevin

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Hi Kevin,

I've been trying to fix some stuff very much like this lately.

I can tell you that yes you should see 12.6V on both sides of the backlight fuse. My guess is that your 11.71 is probably a multimeter error---that's what mine turned out to be on the last board.

Next, you will need to figure out on your own how to source your schematic and boardview for your particular motherboard 820-2915. Once you have those tools, you'll be able to know exactly which component to test, and where to find it on your board.

Your first stop will be to measure the voltages at the LVDS connector itself. I just glanced at your schematic and it looks like you should be seeing 3.3V at pins 2 and 3 on your connector (with display attached and laptop on).

And you should be seeing around 27V at pins 39/40 and on a nearby capacitor C9000.

On the last no backlight board I had, I saw the same 12V coming through to these pins at the LVDS. This means that the LED backlight driver chip--U9701--was not boosting. Probably because I had burned it up :) Of course if I had not seen the 12V and saw only 0V, that would mean that there was a short to ground somewhere between the connector and the source voltage. This is the kind of thinking you'll need to learn as you go on this problem.

I had to send my board out to my talented friend Louis Rossmann and he of course was able to switch out U9701 and the whole thing fixed within 90 seconds. Curses!

I think the backlight circuit on these boards is a very reasonable place to start to try and figure out how to work between the schematic and board to do some troubleshooting.

Report back with what you find as you begin measuring around U9701 and the LVDS connector. Start with voltage measurements as you are doing now, and then we can go short hunting if we need to on diode mode later.

good luck!

jessa

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Hmmmm---and are you Kevin Marquess? I remember him posting a no display question in another forum earlier today. Coincidence?

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hey thanks for the reply... No a different Kevin....

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Also, mine is 820-2936-B 2011 MBP 13"

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great--did you find your schematic and boardview?

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On that board, you want to test pins 21 and 22 on the LVDS connector for your backlight voltage--27V (which means that it would be turning on) or 12V--which means your LED backlight driver chip is dead. or 0V--which means something else is wrong.

What did you find?

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Firstly this makes no sense. You have a picture of a 15" board, with an arrow to the PP3V42_G3H inductor which has nothing to do with backlight. In the title you say a 13.3" board, which would be an 820-2936. Clarify what we're talking about here! If you have a green light on the magsafe PP3V42_G3H supply works and that part is fine. Chipped plastic means nothing on the casing of a huge inductor.

Secondly looking for backlight before there is image is not how we do this. If there so screen activation, meaning you see it blink from black, to a slightly different black, then backlight is not the issue - screen not enabling is. This is a totally separate problem.

Does this even chime? The dong when it turns on. If it does, then we begin troubleshooting no image, but most likely we are troubleshooting something else entirely if there is no recognition of a screen via displayport OR internal LVDS!

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Hi Louis. Don't get cranky--he says he has board 820-2936, and he says tested the LCD with a flashlight and can see the system booting = I took this to mean he sees an image.

So Kevin--can you confirm? What are you seeing on the screen with your flashlight?

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Morning all

Hey Louis....I have been watching your youtube....excellent stuff thanks.

I have a 13" MacBook Pro 2011 with board 820-2936-B. I am certainly not as experienced as anyone on this board... The picture was one I found on the net just to point out the board part that the plastic shield was broke off. I did not know if it was part of the backlight circuit or not.

The system boots and I can see the login etc. I have also attached an external monitor via DVI cable and can use the system no problem. I tried testing the voltage on the LVDS at pin 21 and 22 which was difficult as my meter probe are big...... i will hook up my microscope tonight to get a better close-up. Having said that, I did attach a needle to the red probe to make the tip finer and the voltage I get seemed off.. anyway, that is where I am at. I am thinking from Louis' videos that the U9701 needs to be replaced.... any thoughts thanks. Kevin

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Kevin will be eternally grateful.
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