820-3662 no backlight

[macfix]

Hello Everybody

Working on 820-3662 backlight problem. no liquid damage ..

PPBUS_SW_BLK 0V
PPBUS_SW_LCDBKLT_PWR 12.5V
LCDBKLT_EN_L 12.5V
PPBUS_S0_LCDBKLT to ground resistance is 5.4 Mega ohm
BKLT_EN_R 3.3V

Also replaced , J8300,Q7706,L7710,D7701,Q7701,U7701,U7750

Tested known good LCD, I can hear chime and see dark screen. Any idea for next step?

 

[dukefawks]

Did you check it with the correct LCD? 2012,13,14 will work on these for testing. SMC_LID high?

 

[macfix]

Yes dukefawks checked LCD its for 2012/13 and backlight is working also another mac. SMC_LID is 3.3V

 

[dukefawks]

Diode mode on SMBUS_PCH_DATA and CLK?

 

[macfix]

SMBUS_PCH_DATA is 499Ohm ( Red probe ground at diode mode )
SMBUS_PCH_CLK is 500Ohm ( Red probe ground at diode mode )
same value is LCD connected and disconnected.

Voltage is 3.3V both line when machine running .

 

[dukefawks]

Voltages on all pins of U7701. I can hardy believe this problem "just" happened. What is the history?

 

[macfix]

U7701 voltages is;

1 - 0,02V
2 - 0,02V
3 - 0V
4 - 0v
5- 5V
6- 5V
7- 0V
8- 0V
9- 12.5V
10- 12.5V
11- 12.5V
12- 0 V
13- 1.2V
14- 1.1V
15- 4.4V
16- 4.4 V
17- 3.3 V
18- 5.02V
19- 0V
20- 0V
21- 0V
22- 0V
23- 0V
24- 0V


Owner said suddenly stopped but some one worked on this place

 

[dukefawks]

If pin 6 has 5V what should be on pin 8? Although this is for KB bklt, there is something not right with that. I doubt this will cause issues with LCD bklt.

Pins 15 and 16 are i2c bus, check for data on this bus with O-scope.