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Logic Board 820-01958-A no display

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    #1

    Logic Board 820-01958-A no display

    Today I am working on Macbook Air A2179 2020 logic board # 820-01958-A. It turns on fine but no display. I see the amp meter taking amps from 0.14v to 0.18v (without the battery terminal attached). 20V is perfectly entering the motherboard. The CPU gets hot but no image at all. I am assuming it might be the backlight problem. Even I get ticks feels on the Trackpad. Lid volts 1.8 is all good too. Upon checking the backlight, I checked the 1st MOSFET Q8400, Pin 4 has 12v, this seems to be right but no output pins 1-2-5-6. Pin 3 which is LCDBKLT_EN_L also has 12v which is not right. On this pin it should be around 5.23v approx . I tried with another good LCD screen (just the glass), I use a torch behind, cannot seem to see anything. Any tips will be greatly appreciated. Thanks in advance
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    #2
    Re: Logic Board 820-01958-A no display

    Caps key led toggles?

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      #3
      Re: Logic Board 820-01958-A no display

      mon2, thanks for the reply... First thing I observed this, NO caps LED. But I checked the voltages on all inductor coils, they are present. What you think., from where should I start?? I was thinking it's backlight problem, but this maybe not it., ENABLE even is missing on the backlight chip, all other voltages are present. PRAM senses as when I do it the display on the amp meter resets too. So I know this is working.

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        #4
        Re: Logic Board 820-01958-A no display

        Upon more trouble shooting I found that this rail PP3V3_G3SSW_SNS is missing, this is a TRUE 3.3V rail. It is generating from U8225. When checked U8225 (SLG5AP1445V). Pin # 2 is enable (SENSOR_PWR_EN coming from U7800 pin #152) & this pin should be getting some voltage like 1.8V ~ 3V but this pin is 0V & same with pin 7 (P3V3SEN_SS) out here too it's ZERO. Pin # 1 & 3 are correct 3.3.v (PP3V3_G3H). Can omeone could share their thoughts on this repair & check whether I am troubleshooting correctly. Thanks in advance.

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          #5
          Re: Logic Board 820-01958-A no display

          CPU getting hot but does the fan spin? If yes, then you could check around U8500. I also got this board with the same problem but U8500 is shorted. After replaced U8500 I got display but no backlight. R8444/U8400 need to be replaced also to get the backlight.

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            #6
            Re: Logic Board 820-01958-A no display

            Hey "anhbanxoi", thanks for your reply. There is NO fan spin at all. Even after a PRAM reset, no Fan Spin. I checked U8500 (MOSFET) & R8444, seems to be ok. & I think backlight circuit might be working, U8400 is not even getting the ENABLE signal at Pn 17 of this chip. The Caps Lock LED even does not light up & no Fan spin but I can feel that the trackpad is creating that ticking feel. Any more tips will be much appreciated. Thanks

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              #7
              Re: Logic Board 820-01958-A no display

              Try restore with Apple Configurator in DFU mode then check if you get ALL_SYS_PWRGD signal.

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                #8
                Re: Logic Board 820-01958-A no display

                Thanks buddy... I am getting ALL_SYS_PWRGD signal 1.4V.. Think this voltage is ok or it should be 1.8V???

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                  #9
                  Re: Logic Board 820-01958-A no display

                  That is low. It should be 1v8.

                  Check the voltage to ground of PP1V8_PRIM_PCH.

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                    #10
                    Re: Logic Board 820-01958-A no display

                    Originally posted by mon2 View Post
                    That is low. It should be 1v8.

                    Check the voltage to ground of PP1V8_PRIM_PCH.
                    Excatly 1.8V on L7701 coil. Voltage out here is perfect.

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