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820-01700 No Backlight

J

javier_herart

Member
Hello.

No backlight on this machine:

F8400: ok and no short
LCDBKLT_EN_L: 12V
PPVIN_S0SW_LCDBKLT_R: 12.58V
LCDBKLT_EN_L: 12.58V (this is wrong right?)
PP5V_G3S_BKLT_D: 5.1V
PP5V_G3S_BKLT_A: 5.1V
BKLT_EN_R: 3.3V

Any help? Thanks!
 
J

javier_herart

Member
No history available, no liquid damage.

Yes, I do get image on the screen but no backlight.

PP5V_S0SW_LCD: 5V
PP3V3_S0SW_LCD: 3.3V
DP_INT_HPD: 3.3V
 
2informaticos

2informaticos

Administrator
Staff member
Check R8450-53 and their traces.
Be sure to get similar values in voltage and diode mode to ground.

Also check diode mode to ground on both pins of D8410.
 
J

javier_herart

Member
R8450: 0.1ohm (same value in both side in diode mode)
R8451: 0.1ohm (same value in both side in diode mode)
R8452: 1.29Kohm (diode: 0.384V on PP5V_G3S side, 0.536V on I2C_BKLT_SCL side)
R8453: 1.3Kohm (diode: 0.384V on PP5V_G3S side, 0.536V on I2C_BKLT_SDA side)

D8410(1): 0.568V
D8410(2): 0.384V
 
2informaticos

2informaticos

Administrator
Staff member
Do you have continuity from these resistors to J8500 and U8400?

Be sure all the resistors and traces around U8400 are good.
You can try changing U8400, even Q8401.
 
Last edited:
2informaticos

2informaticos

Administrator
Staff member
I doubt to have lid sensor problem, as you get image, only missing backlight; also EDP_BKLT_EN is present.
But is worth to try PRAM reset and SMC reset.

You should also try to get the chip from donor board, same model.
 
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