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[SOLVED]820-2850 no backlight

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  • #16
    But need to understand what screen expect from board to turn on LEDs? Which signals? In laptops expect 12-19V, PWM and enable. And in apple?

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    • #17
      25V is not that low but it could be higher.
      On a working 2010 15" BKL output is 33V and LED return lines are 3.2V so that puts about 30V across the LEDs

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      • #18
        And how do you think these LED driver got burn? This is second macbook pro for 2 weeks. One is 2010 15, and another 2012 15
        Both of them working good, video, backlight. I just opened them to replace a cap and after that backlight is gone. In both cases I found hole in LP8545
        I dont know what wrong I do...why this led driver just got damage. In first case board 2012 I just replaced it and it works good.

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        • #19
          I have no idea, but you are shoving 2012 connectors into 2010 boards.

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          • #20
            About PWM, when it change from 2.2V to 2.5V this should increase VLED from 25V to 30V?

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            • #21
              No idea, 2.5V seems low. We can talk about this all day but you need to swap the LP8545 and check all resistors.

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              • #22
                Will replace LP8545 again and will compare with another board I have here for parts.
                It is possible to test screen connecting 30V to VLED directly? Will turn on the leds or it is no enought? This way also I can check if leds turn on at 27,28 or 29V

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                • #23
                  Negative to LED return lines and positive to the BKL Vout. LEDS should light at about 30V. But do this with a variable power supply and go up from 20V till they light up.

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                  • #24
                    Sorry, you mean I have to put all 6 return lines to negative? And PPVOUT_S0_LCDBKLT to power supply. 20-30V

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                    • #25
                      Why do you even want to mess with this? This is not going to fix the board. I gave you the correct voltages from the board.

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                      • #26
                        Finally I got this board working. Resume: I found LP8545 damage and no backlight. After I replaced this IC with new one I got only 25V and no backlight. I replaced it again with new one same provider and again only 25V and no backlight. I replaced it again and the same. Always check carrefuly how this chip is solder and I solder this chip perfectly.

                        Then I took this chip from my board for parts and now backlight works and I have 33V

                        New chip from SEE-IC I got is written on it: VM08AD 45-EXTF. This chip doesnot work for me. I got only 25V with this chip. Could be fake chip? Or not exact part number they sent to me?

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                        • #27
                          These chips have en EEPROM inside. Maybe they are programmed for something. A blank default EEPROM normally works.

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                          • #28
                            Never find a not working new chip?

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                            • #29
                              I don't buy these new chips, enough donor boards in the pile.

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