820-3476-A No Backlight

[myiannakou]

No backlight

Some readings

U7700
Pin 1&2 LCDBKLT_SW = 0.1v
Pin 4 LCDBKLT_FET_DRV = 0v
Pin 5 PP5V_S0_BKLT_D = 5.15v
Pin 18 PP5V_S0_BKLT_A = 5.15v
Pin 17 BKLT_EN_R = 3.34v

Thank you

 

[2informaticos]

Post D7710 voltages.

 

[myiannakou]

D7710 voltages.
Pin 1 (PPVIN_SW_LCDBKLT_SW) = 0.01v
Pin 2 (PPVOUT_S0_LCDBKLT) = 0v

 

[2informaticos]

Check BKLT_SD,
If good, check F7700.

 

[myiannakou]

12.38v bklt_sd
12.56v both sides of f7700
Fuse has continuity

 

[2informaticos]

"12.38v bklt_sd
---------
If good"
Is NOT!

Did you try another compatible LCD assembly?
Check R7750-53 and traces.
Post voltage and diode mode on SCL/SDA lines.

 

[myiannakou]

What should BKLT_SD be to be good? LCD Assembly good tried on working MacBook.

BKLT_SCL = 4.62v 0.468
BKLT_SDA = 4.54v 0.464
R7750 to 53 all good. Traces appear fine.

 

[2informaticos]

Backlight adjust is controlled through I2C bus, via PCH -> T-CON -> U7700.
BKLT_SD must be 0V, in working state; controlled as mentioned.

Try chabging U700.
Check all its connections.
Be sure no short anywhere.

 

[myiannakou]

I don't understand "change U700" ?

 

[myiannakou]

If you mean U7700 then I have changed it but the same problem persists. Thanks

I will check to see if there are any shorts to its connectors

 

[myiannakou]

When I'm checking voltages at U7700 should I have the screen plugged in or does it not make a difference?

 

[2informaticos]

Yeah, U7700.
I supposed all previous readings are with LCD connected.
If not, wasted time...

 

[myiannakou]

Yes all readings were carried out WITHOUT screen connected.
Shall I do them again with screen connected and send them too you?

 

[2informaticos]

Of course.
How do you expect to get backlight voltage, if no LCD connected.
I already explained you the via for required communication; T-CON is inside LCD assembly!

 

[myiannakou]

There was a short on PPVOUT_SO_LCDBKLT caused by a bad LVDS connector. Replaced connector and now all good. Thanks again for your help and support. Until the next one - Adios!