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820-2850 chimes No backlight or image

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  • 820-2850 chimes No backlight or image

    I got this board today, I was a able to get video out of it once out of probably 15 power cycles. It does chime every power cycle. I ran out of time today at work to start measuring power rails. Am I correct in thinking this is a 330uf tantalum cap problem (c9560)? Or at least a good starting point?
    Last edited by cpdist; 09-18-2016, 09:51 PM.

  • #2
    Replace C9560 first, but I doubt that will be it. Try a known good LCD assembly too and disconnect the battery indicator.

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    • #3
      I replaced c9560, and also just got my known good screen, still same issue not able to get image or backlight. I get chime every time.

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      • #4
        Does it work with an external screen?
        I had similar symptoms on a different board. Take a look from U9000; around L9000, L9010, L9011 area.

        I had a corroded L9080 (your board doesn't have this particular part no.) which was near the DC Adapter. Classic moisture / liquid damage.

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        • #5
          Yes, check external video and then check SMC_LID, should be 3.3V .Then check power to pin 4 6 and 7 of LCD connector. Measure them in diode mode too, with and without LCD plugged in.

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          • #6
            External video does not work,
            SMC_LID Probe

            R5071 3.3v



            w/ screen
            PIN 4 = 3.2v
            PIN 6 = 3.2v
            PIN 7 = 3.2v

            Diode Mode

            PIN 4 = 0.27
            PIN 6 = 0.45
            PIN 7 = 0.46

            W/o Screen

            PIN 4 = 3.3v
            PIN 6 = 3.2v
            PIN 7 = 3.2v

            Diode Mode

            PIN 4 = 0.27
            PIN 6 = 0.45
            PIN 7 = 0.45


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            • #7
              Hmmm, you should get video externally with VGA or HDMI adapter at least if you leave internal LCD disconnected.
              Try heating up the GPU to about 100C and try again.

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              • #8
                Heated the gpu up to 100c, tried again issue remains.

                An observation I made when I had the board out is that after the chime the fans rev up to full speed and remain there they do not throttle down. This was happening before and after heating the board. Dont know if that mean anything to this issue.

                I did try external video again after heating with and without the lvds cable plugged in.
                Last edited by cpdist; 10-04-2016, 01:54 PM.

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                • #9
                  Any history on this board? GPU not messed with? It's worrying that you were able to get video at one stage, usually does not bode well. GPU getting power?
                  Try pressing on the MUX chip and powering on too.

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                  • #10
                    The board looks un-sodomized no signs of previous work. I have not done anything to it besides what we have discussed. Out of probably over 100 power cycles since I have been testing it I have maybe gotten video 5 times. Ill let you know on the MUX/GPU stuff. Thanks Duke!

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                    • #11
                      Decided to take keep messing with this board. I took some measurements regarding the GPU power, I also tried pushing on the MUX while powering it on.

                      PP1v05_S0GPU = 1.05v
                      PP1V8R1V55_S0GPU_ISNS = 1.33v
                      PP1V8R1V55_S0GPU_ISNS_R = 1.33v
                      PP1V8_GPUIFPX = 1.78v
                      PP3V3_S0GPU = 3.28v
                      PPVCORE_GPU = 0.9v
                      PPVCORE_S0_GFX = 0.87v



                      LVDS connector

                      PINS 2&3 - 3.2v

                      PINS 39&40 - 24.9v

                      Machine continues to power on and chime. After about 5 seconds the fans go to 100% and just sit there with no video. Any other suggestions?

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                      • #12
                        3V on pin 2 and 3 suggests there IS an image on the LCD! 24V on backlight means there is just no backlight......

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                        • #13
                          You are correct sir my apologies for confusing the situation. I can usually see the image with my nake eye but this time I had to use a flash light to see the blinking folder but it is there. So to figure out why I have no back light.

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                          • #14
                            BKL_PWM on R9704? Did you do a PRAM reset?

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