Released October 2008 / 2.4, 2.53, 2.66, 2.8 or 2.93 GHz Core 2 Duo Processor

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Why I can't get backlight on screen

Hello Guys,

Was wondering if someone could lend some expertise into this problem. I have a late 2008 MacBook Pro unibody 15.4 and the backlight is not working. I can use external monitor and I can see all images when shining a bright light at the screen, but no backlight. This is what was done so far;

1-replaced the logic board twice, same problem no backlight

2-replaced the LCD screen no backlight

3-I now have a third logic board and no backlight

I really don't think it could be three bad logic boards!

Question, could it be a bad LVDS cable?

Any help would be appreciated.

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Your LCD or LCD cable is &&^&^$^ up the boards. You'll need to give an 820 number for your logic board(NOT 820-2565 THIS IS A DCIN BOARD NOT A LOGIC BOARD) so we know what backlight circuit yours uses, and so you can buy a schematic and a boardview online somewhere so you can follow along with our advice.

Start by measuring voltage on pins 38/39/40(they're all tied together) on the LVDS connector, and see what you get. Also measure with LCD cable plugged IN, and NOT plugged in, in diode mode on your multimeter, with red probe on ground, black probe on pins 38/39/40, and provide measurements here.

0.519-0.546 means healthy.

0.2** means bad LED driver.

0.00 or 0.019 means there is a direct short to ground in either the connector, or the LCD/LCD cable itself.

Resistance is NOT diode mode, so figure out how to set your multimeter to diode mode.

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The board number is 820-2330-A

Louis thank you for the info. I'am really not a electronics expert like you, but I do have some minor electronic skills. However, I am trying to find a diagram of the LVDS pin sequence and can't seen to find it. While looking at the connector being top right corner pins 38,39,40 would be to the right? Also, checking diode mode without power to unit right?

All info you will find in the schematic/boardview that you buy if you will be troubleshooting this at component level. You need that before we go further or do anything. First assignment is to find it.

Louis I did find the schematic of the board online. It shows all the components and also the backlight in and out of the LVDS cable. I just got done checking voltage across pins 38,39,40 found 0.00 volts in diode mode I found 2.57. So by your educated guess it looks like the WLED chip. Question? If it is this chip can I get the chip and try to accomplish this? Also, the small 0402 package fuse is testing ok through continuity. Thanks for all your help! I watch your video on soldering this chip and I was thinking that I could accomplish this. I would just send you the board and have you fix it, but because it is so old I don't want to put much money into it. So I wanted to fool with it myself. Again, a great learning experience and kudos to you, I like a guy who really takes interest in what he's doing. I do the same in my business.

Thank you for the help!

Roger

0.257 or 2.57? Red probe on ground and black probe on pins 38/39/40, right?

Even if the LED driver is &&^&@@, if the fuse is good you should see 12.6v on the pins. Follow along on the path after the fuse and see when the 12.6v goes away. An LCD with a working image on it must be plugged in while you do this.

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