A1390 820-3332-A No Backlight

[philo]

Hey guys, i received this 15" MBP Retina previously touched by other messy hands. They previously attempted to disable graphics card but i removed the jumpers and took everything back as it was, I resoldered U8900 and got video output through the screen and loaded to operating system (throught HDMI it does give picture but somewhy it crashes before it can even load the progress bar, gray screen appears with "Your computer restarted because there was a problem").

Getting back to the issue, the chime sounds distorted, and still don´t have backlight (the water indicator on the backlight zone is red, client says it never got liquids spilled ).
No voltage at Pin 1 of J9000, PPVOUT_S0_LCDBKLT.

Backlight diodes, and filter caps are not shorted to GND neither show low resistance. I´ve got this readings on the Backlight IC:

U9701:
Pin 2 (LVDS_BKL_PWM_RC) :1,44v
Pin 4 (BKLT_EN): 0v
Pin 6 (BKL_FET_CNTL): 0v
Pin 8 (PP3V3_S0): 3.3v
Pin 10 & 11: (BKL_SDA & BKL SCL): both 3.3v
Pin 22 & 23(PP5V_S0): 5v
Pin 24(BKL_SW): 0.3v

D9701: 0v

Q9706:
Pin 1: 12.57v
Pin 2: 12.57v
Pin 3: 4.11v
Pin 4: 12.57v
Pin 5: 12.57v
Pin 6: 12.57v

Appreciate any clue or help, I suspected of backlight IC but unluckly havent got any to test

[mon2]

Re: A1390 820-3332-A No Backlight

hi.

1) I think that 820-3332-A = A1398

2)

U9701:
Pin 4 (BKLT_EN): 0v

So backlight will be disabled.

Review and post the voltage values for the referenced locations.

3) voltage on PPBUS_S0_LCDBKLT_PWR = L9710, pin 1 ?

4) voltage on R9731, pin 1 = PPBUS_S0_LCDBKLT_PWR ?

[philo]

Re: A1390 820-3332-A No Backlight

hi.

1) I think that 820-3332-A = A1398

2)


So backlight will be disabled.

Review and post the voltage values for the referenced locations.

3) voltage on PPBUS_S0_LCDBKLT_PWR = L9710, pin 1 ?

4) voltage on R9731, pin 1 = PPBUS_S0_LCDBKLT_PWR ?

Hey!

1) right

2) Reference voltages;
1> 12.56v / 2> 0.023v / 3> 3.33v / 4> 12.201v / 5> 0.001v / 6> 12.56v

3) 0v on L9710

4) 0v on pin 1 R9731

Thanks

[philo]

Re: A1390 820-3332-A No Backlight

hi.

1) I think that 820-3332-A = A1398

2)


So backlight will be disabled.

Review and post the voltage values for the referenced locations.

3) voltage on PPBUS_S0_LCDBKLT_PWR = L9710, pin 1 ?

4) voltage on R9731, pin 1 = PPBUS_S0_LCDBKLT_PWR ?

If it helps I previously attempted this: I jumped (LCD_BKLT_EN) to PP3V3_S0 in the U9100 area, and at pin 1 of LCD connector (PPVOUT_S0_LCDBKLT) I got 12.54v.

[philo]

Re: A1390 820-3332-A No Backlight

Anyone?

[mon2]

Re: A1390 820-3332-A No Backlight

PPVOUT_S0_LCDBKLT - I got 12.54v

With the bypass trick, this rail is still too low for the backlight.

Perhaps consider to replace U9701 (LP8545SQX-EXTJ).

From assorted other posts, the backlight will enable only if the LCD is detected. However, if you are bypassing the turn on logic with your own external logic levels then this boost power supply should just enable and generate the much higher boosted voltage.

Suggest to continue to try your bypass method but remove the LCD display till the backlight voltage is deemed to be a safe and 'normal' value. In my opinion, U9701 is only a boost power supply that should operate as designed once the enable and supporting components are functional.


https://www.aliexpress.com/item/4000...archweb201603_

I think you can source the same part (different suffix) directly from TI.com webstore:

https://www.ti.com/store/ti/en/p/pro...-findchips-wwe

Not sure if Apple had a custom version of this component manufactured for them but confirmed through the datasheet that at least the I2C slave address for this device matches the Apple schematics. Perhaps someone in the forum has sourced the original TI to replace this component with success ? It is worth a try and may be easily available through your local electronic parts resellers.

[philo]

Re: A1390 820-3332-A No Backlight

Hey! Once again thanks for your help, really appreciate it. I also have the idea that the IC is bad, just want to make 100% it is before I can order it (it would take aprox 45 days to arrive to my country).
My new update: having those 12.54v on the backlight rail I decided to hook up and external PSU of 45Volts to the rail, but still the same result: no backlight. It stays in stable 45v with the external PSU

[philo]

Re: A1390 820-3332-A No Backlight

Btw keyboard doesn't work (except for power key), and touchpad neither. Maybe it's all an SMC issue?