[SOLVED]820-3115 No Backlight

[Jay]

Tested with good display, also no backlight. Unit chimes and Image is visible with flashlight. No liquid damage that I can tell.
Having difficulty narrowing down the problem.

Here's what I got so far:
C9799 - 12.52V
C9797 - 12.52V
C9796 - 12.52V
L9701 - 12.55V
R0910 - 12.5V
U9701 - 3.1V pin 3 // 007.0mV pin 6
C9712/13 - 12.55V
Q9706 - 4.35V pin 3 // 12.55V all other pins
L9080 - 1.2V all pins // all traces good
F9700 - 12.5V both sides
C9711 - 3.3V pin 1
J9000 - 3.3V pins 4, 6, 7 // 12.6V pins 21, 22 (connector and all pins look good)
R9715 - 3.1V pin 2
R5071 - 3.4V both pins

There are a few slightly discolored probe points in the U9701 area but no signs of liquid exposure or corrosion anywhere.

 

[dukefawks]

PRAM reset done? Check BKL_PWM voltage.

 

[Jay]

PRAM Reset was done, issue persists.
BKL_PWM (measured on C9704 and R9704) = 3.3V

 

[dukefawks]

Bad LP8550 or a corroded feedback trace.

 

[Jay]

Removed U9701 and checked all traces, everything OK there. Ordered replacement U9701 and will see where that takes me.

 

[Jay]

Finally got around to continuing work on this machine. U9701 was replaced and now I get no power, no chime, just a quarter fan spin.
When I listen close there is a buzzing sound coming from the fan when I press the power button.
Magsafe light is ok, green at first then red because battery is empty.
When battery is disconnected, magsafe shows green with a constant quick flicker about 2-3 times per second.

Where do I go from here?

Could the U9701 be oriented wrong? I assumed the dot on the new chip corresponds with the dot on the old chip.

 

[Gurmon]

Post picture of u9701 for us to check or remove it see if the board fires up.

 

[Jay]

No Title

Will remove it tomorrow to check for power, didn’t think of that..

chip was ordered from mailin.repair, didn’t come from a donor board.

 

[dukefawks]

I'm pretty sure I see balls squishing out. Did you touch it when reflowing? Remove it and see if board works again.

 

[Jay]

A bit of solder did pop out the side.
Chip came with balls on it so I wicked the pads (I already put some solder on), put some flux, flowed in the new chip.

Let me guess, I’m not supposed to push it down on the board? (Because I did)

 

[dukefawks]

Pushing it down is a sure way to short all the balls together. Pull it off and put another chip, do not touch it while reflowing.

 

[Jay]

No Title

Lesson learned, don't push U9701 to the board
Removed, wicked, placed another one (properly) and we got a happy Mac with power and backlight.
Thanks for all the help!