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The feedback resistor was corroted , Now backlight is working . I have also seen L8504 was burned , Since the U5610 not equipped I have just removed that inductor, Do you know whats the purpose of this circuitry ?

I think I have to remove the board and check the voltages on U8400 ?

Yes it is the value with red probe at ground. I don't have a working board with me sorry☹️

Diode mode - 1.150V with and without LCD

Yes, Confirmed that it is not a displayed problem, Even with the a1706 display it has the same behavior, No backlight. Either the boost circuitry not working or it is the flex cable between the display and Motherboard?

Removing J501 I could see the fans running, starting with low speed and keep increasing to high speed, No other difference.Battery connectors also removed, Doesn't made any change.

LCDBKLT_EN_L stays high 12V ,PP5V_G3S is 5.1V

Sometimes I can see even higher voltage (Upto 12V) But not consistent, Keep reducing

(PPVOUT_S0_LCDBKLT) is 1.6V which is not consistent its keep reducing

Just out of curiosity, https://boards.rossmanngroup.com/threads/a1706-emc3163-touch-bar-not-working-after-display-replacement.61221/page-2#post-76380 >>>> In this case also the same rails were missing, How did you conclude that it is a dead CPU?

820-00850-A Apple 2.7 i7 16GB 1TB Logic Board A1989 MACBOOK PRO 13 2018 I hope this is the one

L7430 - PPVCCGT_S0_CPU - 0V L7420 - PPVCCGT_S0_CPU - 0V L7410 - PPVCCGT_S0_CPU - 0V Isn't these voltages are not necessary?

Back to this board , PPVCC_S0_CPU is stable , I don't see fluctuation on any of the rails L3500 - P5VUSBC_X_R - 0V L8410 - PPVOUT_S0_LCDBKLT -0V L7030 - PPBUS_G3H - 13.11V L7660 - PP3V3_S5 - 3.367V C7651 - PP5V_S5 - 5.150 L7600 - PP5V_S4 - 5.153V L7700 - PPVCCEDRAM_S0_REG_F - 1.056 L7430 -...

Is there an option to check the serial number without removing the board?

Is there anything I can do, Or I should scrap this board? Is there any option to confirm it is the CPU that is dead? Maybe a stupid question, Will it be possible to replace the CPU by a professional micro soldering company?

Really?☹️

Hi, I have replaced U7420, Now all the voltages are there except PPVCCSA_S0_CPU and PPVCC_S0_CPU. There is some common signal missing, I couldn't check the PWM pin. CPUCORE_FCCM is 0V and PVCC is 13V and PP5V_S0_VCORE is 5V.

Could you help me with the schematic and layout of A1989 ?

The user said that the system was working fine and suddenly one day its backlight was missing. I can see the laptop has been already opened by someone. Even the display assembly also opened. I have an A1706 display spare for testing, Will it work?. I don't have an A1989 working display to...

Yes, everything solved, Fan connecter was lost, Then I have removed and cleaned the display connector. Now the system works perfectly so far