macbook pro a1989 power on but black screen

[reset1986]

hi everyone, i have this macbook pro with 820-00850a motherboard,
at the beginning it had burn marks on the flat connector on the display side, replaced the flat and connector on the display side but the problem remains,

when I turn on I hear the boing, the keyboard lights up but there is no display activity, even in backlight there is no image,
checked fuse, there are no short circuits,
suggestions?
I don't own spare display
from the measurements are missing
PPVIN_S0SW_LCDBKLT 0 V
CPUGT_SW1 0V
PVCCEDRAM 0V

thanks

[mon2]

Re: macbook pro a1989 power on but black screen

1) Try a PRAM reset

2) Post the voltage readings for:

PP5V_S0SW_LCD

PPVOUT_S0_LCDBKLT

PPVIN_S0SW_LCDBKLT

LCDBKLT_EN_L

PPVIN_S0SW_LCDBKLT_F

BKLT_EN_R

EDP_BKLT_EN

I2C_TCON_SDA

I2C_TCON_SCL

[reset1986]

Re: macbook pro a1989 power on but black screen

1) Try a PRAM reset
2) Post the voltage readings for:


PP5V_S0SW_LCD

PPVOUT_S0_LCDBKLT

PPVIN_S0SW_LCDBKLT

LCDBKLT_EN_L

PPVIN_S0SW_LCDBKLT_F

BKLT_EN_R

EDP_BKLT_EN

I2C_TCON_SDA

I2C_TCON_SCL

ok,mesure

PP5V_S0SW_LCD 5 V

PPVOUT_S0_LCDBKLT 0 V

PPVIN_S0SW_LCDBKLT 0V

LCDBKLT_EN_L 12.5 V

PPVIN_S0SW_LCDBKLT_F 12.5 V

BKLT_EN_R 0V

EDP_BKLT_EN 0V

I2C_TCON_SDA 3.3V

I2C_TCON_SCL 3.3 V


all measurements were made with the display disconnected with the power cable only

replaced q8400, always no display signal
thanks

[reset1986]

Re: macbook pro a1989 power on but black screen

PPVIN_S0SW_LCDBKLT must it always be 12.5v even with the panel disconnected?

[piernov]

Re: macbook pro a1989 power on but black screen

Diode mode to ground EDP_INT_AUX_N EDP_INT_AUX_P

[reset1986]

Re: macbook pro a1989 power on but black screen

Diode mode to ground EDP_INT_AUX_N EDP_INT_AUX_P

sorry for the delay, I had put this mac aside, today I try the values of the 2 signals and let you know, thanks:pensiero:

[reset1986]

Re: macbook pro a1989 power on but black screen

Diode mode to ground EDP_INT_AUX_N EDP_INT_AUX_P

EDP_INT_AUX_N in short,

EDP_INT_AUX_P correct value,

measured in diode mode,


EDP_INT_AUX_N is generated by the cpu,

cpu broken?

[reformatt]

Re: macbook pro a1989 power on but black screen

Louis has covered this design issue a few times. Pin 43 (PPVOUT_S0_LCDBKLT) and Pin 1 (EDP_INT_AUX_N) are side by side on J8500. Any liquid damage to this connector can potentially allow that high voltage into that data line and damaging the CPU. Crazy design.

[Strolch]

Re: macbook pro a1989 power on but black screen

Louis addressed this design issue a couple of times. Pin 43 (PPVOUT_S0_LCDBKLT) and pin 1 (EDP_INT_AUX_N) are next to each other on J8500. Any liquid damage to this connector could potentially allow this high voltage to enter this data line and damage the CPU. Doesn't the A1989 have a chip like the U9850 that can be swapped out, like the A1707? Is the CPU definitely affected in this case? On my board, pin 43 and pin 1 also had a short circuit!