820-02020 No video

[carlosaovalle]

Hi! This MacBook came to me with no power due to water damage. I found corrosion in the UP701 Area, I cleaned the area and the computer started working again . After putting all components back together, the computer worked for a couple of minutes normally with image . After a couple of minutes the image was gone . I hear the chime but not image.

I replaced UP701.

Voltages :
PP3V3_S2 2.16v
PP3V3_SW_LCD_CONN 2.16V
PPVOUT_LCDBKLT 0.01v
PP5V_SW_LCD_CONN 5.2V

Diode Mode reading:

PPVOUT_LCDBKLT 1670 (not sure if this is normal)

 

[2informaticos]

First of all, welcome to the forum!

Check RD560 and its traces.
If good, post UC710 voltages; pins 1, 8, 5, 2.

 

[carlosaovalle]

Thanks for welcome me!

RD560 looks intact
pin 1 0.57v
pin 2 0.57
pin 3 12.5V
pin 4 12.5V

UC710
Pin 1 12.5V
Pin2 1.8V
Pin 2 1.75V
Pin 5 0.7V

 

[2informaticos]

RD560 must have same voltage on all 4 pins.
However, important is to get 12.5V at UC710.
That means RD560 is good.

"Pin2 1.8V
Pin 2 1.75V"
I can't understand that.
You've reported 2.16V at LC710...

Check all RC709-13 resistors and their traces.
You may need to change UC710.
Pay atention when you work on that area.

 

[carlosaovalle]

I'll order UC710 online. Once I replace it, Ill post the outcome. Thanks a lot

 

[2informaticos]

Post again (correctly) UC710 voltages.
Please, pay more atention when you write a post.

 

[carlosaovalle]

UC710 Voltages

Pin 1 12.35v
Pin 2 1.75v
Pin 5 0.7V
Pin 8 1.77v

Now Fan is Spinning at High Speed.

 

[2informaticos]

"Check all RC709-13 resistors and their traces."
All five resistors and traces good for sure?
If yes, then UC710 is bad.

Just in case, remove it and resolder with leaded solder.

 

[carlosaovalle]

Good Morning!

RC709-13 traces are in good shape. I don't see anything abnormal.

All resistor readings are fine except RC712 it should be 127K, the multimeter shows 34.5k.

 

[2informaticos]

Onboard readings for high value resistors is not correct.
When in doubt, remove the resistor and check it out.

0.7V on feedback pin is good.
If all resistors from feedback network are good, then bad UC710.

 

[carlosaovalle]

Thanks a lot!

 

[carlosaovalle]

What about this?

PPVOUT_LCDBKLT 0.01v
Diode Move Value 1628

is it normal at this point?

 

[2informaticos]

Don't waste time with backlight before getting correct 3V3_S2 voltage.

Just in case, check diode mode around UP701.
You may need to resolder, or change it again.