820-2936 no backlight

[Kyle93]

Had mild water damage. Replaced U9701 twice and U9000

U9000 pin 2 and 3 3.3V pin 1 0V

r9731V 0V

what to check next?

 

[JohnB8812]

Diode mode in backlight output?

 

[Kyle93]

Ppvout_sw_lcdbklt 0.571

 

[JohnB8812]

Seems high like an issue around the switch trace of LP8550. Definitely no short on backlight? Fuse ok?

 

[2informaticos]

Any voltage at pins 2, 3, 4 of J9000?
You don't get image, why looking for backlight???

Check if board has USB activity.
Do you hear chime at least?

 

[JohnB8812]

Oh wait my bad I thought he said 3.3 at the connector not U9000. Yes check for USB activity/chime first

 

[Kyle93]

No chime or usb activity but have 1.1V vcore.

Bios issue?

 

[Kyle93]

J9000 0v pins 2 and 3 but 3.3V on pin 4

 

[JohnB8812]

No chime and USB activity points to a whole different issue. Could be a BIOS issue in this case. Try a new one for testing and keep the old one in case it is the actual issue.

 

[2informaticos]

Also try one DDR3 module at a time, each slot by separate.

 

[Kyle93]

tried new bios and one DDR3 module at a time with no change.

SMC issue?

 

[JohnB8812]

Does it start in SMC bypass?

 

[2informaticos]

Where was the liquid spill?

 

[Kyle93]

SMC bypass mode made no difference, just fast fan spin but still nothing on the screen.

liquid spill was only in lcd area

 

[2informaticos]

When board properly boots, you should note a drop from 1.1V to aprox 0.8V for CPU VCORE.
LVDS lines go from J9000 to PCH, which could got affected by liquid spill...

 

[Kyle93]

Checked and CPU VCORE is at a steady 1.1V and does not drop.

 

[2informaticos]

Try to reball SMC.
If no result change it.

 

[Kyle93]

reballed SMC and no result.

Also changed SMC and still no result. After a few seconds i get one blink from white led every few seconds. Makes no difference if ram is inserted or not.

VCORE still steady 1.1V

 

[2informaticos]

I suppose bad PCH, or CPU.
Can also be something affected by liquid.
Reflow them with good flux.

 

[Kyle93]

replaced r7402 and now have chime but still no backlight.

J9000 3.2v pins 2, 3, 4.

Already replaced u9701