No Backlight - 820-00426A

[LCDR2]

Hi

Client claims laptop was water damaged and he ordered a new board from overseas.

With this new board he has no backlight. I've tested a different screen on this computer there is also no backlight.

A1398 EMC2909 (original model)

I assume I would start by checking backlight circuit output etc?

Basic stuff I've tried SMC reset etc.

 

[2informaticos]

Image present, only missing backlight?

 

[LCDR2]

correct. image booting perfectly.

 

[LCDR2]

I have replaced battery with no change. User battery swollen

 

[2informaticos]

Do you get any voltage at pin 1 of J8300?
Post BKLT_EN_R and BKLT_SD.

 

[LCDR2]

Pin 1 - 2mv
BKLT_EN_R - 1.9mv
BKLT_SD 5.03v

I took a look at the schematic and working my way back on the backlight circuit I've checked ...

U8300 Pin 1 PPV5S4 5.04v
PPV5 FETCAP LCD 5v
PPV5 SW LCD ISNS 5v

Q7701 (Si7812DN N Channel Mosfet)
BKL_SW 54mv
BKL_FET_CRTL_R 0v ... which I think may be the problem ?

In this scenario is Pin 4 the gate?




Thanks in advance,

James

 

[2informaticos]

Do not touch backlight circuit, is not enabled yet.
LCD_BKLT_EN is present?
If yes, check 7742.

 

[LCDR2]

LCD_BKLT_EN is present? - 1.6mv.
1.5mv on R7742 BKLT EN R

I assume you mean the resistor connected to Pin 17 of U7701.

 

[LCDR2]

Could this be a motherboard / screen compatibility issue? Client has also informed me that the webcam also does not work.

 

[2informaticos]

Be sure to test with compatible screen, same year model...