820-4924 no backlight

[Kyle93]

This arrived with no backlight but machine still boots and chimes. minor liquid spill on U8330. Replaced but no change.

There is 5v at the screen but no 0V on backlight. Using a known good screen. EDP_BKLT_EN is only 0.300V

Can this be bad CPU/PCH since EDP_BKLT_EN comes from it?

 

[2informaticos]

DP_INT_HPD steady high?
Can you confirm if image is present?
LCD_PSR_EN goes high?
Do you get 3V at pin 5 of J8300?

 

[Kyle93]

DP_INT_HPD steady 2.4v

Yes image is present

LCD_PSR_EN yes 3.3v

yes 3v at pin 5 of j8300

 

[2informaticos]

Be sure to test with compatible screen for this year model.

 

[Kyle93]

I am. The same screen works fine on another 4924 board

 

[2informaticos]

You should have something more affected by liquid.
Compare diode mode to ground readings on that area with the good board.

 

[Kyle93]

diode mode readings are very close and some exact to good board

 

[2informaticos]

Possibly liquid spill damaged PCH through the backlight control lines.

Just in case, do PRAM reset 2-3 times.
SMC_LID should be high; check it anyway...