No display a1278 820-3115-B

[dclass-pro]

Hi guys, I have this macbook a1278 which doesn't have any image on the display, but when I turn it on I hear the chime.
I found the L9008 choke open and reset it.
When I turn on the macbook I have about 3v on pins 3 and 4 of the display so everything is ok but I still don't have the image.
On the backligt pin 21 and 22 I have 0v but the fuses are all ok.
What can I check?
I tried another display from a macbook a1278 but from the previous year and it still doesn't work.

[mon2]

Check the backlight details by studying this thread:

https://www.badcaps.net/forum/troubl...ht-has-picture

[dclass-pro]

I followed this guide and also tried to change U9701 but I have no changes.
On the D9701 diode I always have 0v on both sides

[mon2]

Are you able to view any graphics on the LCD using a flashlight / phone torch on this display? Also, after a while after turning on the machine, does the caps key led toggle? This confirms that the OS has booted and you are at the login screen.

[dclass-pro]

Unfortunately I don't see any image on the display

[mon2]

What is the history of the laptop? Any liquid damage? Post pics of the lcd connector area. Inspect the contacts of the lcd display but be sure to remove all power before removing the lcd connector for inspection.

For the display to work there must be power and data flow. Perhaps the data lines are not working properly or damage to this area.

[dclass-pro]

I made a mistake in checking, the image is there and the backlight is missing, in fact I see the user at login if I put the flash on the screen... what can I check?

[mon2]

the image is there

Good.

Carefully, measure the voltage to ground of the following points of interest:

R0910 ; check both sides - the main power for the backlight LCD voltage
BKL_EN ; measure at R9715 - one side of this resistor will be ground but other side is BKL_EN - to confirm the backlight is enabled
I2C_BKL_1_SCL ; used to configure the backlight IC
I2C_BKL_1_SDA ; as above
LCD_BKLT_PWM ; used to change the intensity of the backlight - if 0 volts, the LCD will be dark; if 3v3 - lcd will be full brightness on

[dclass-pro]

R0910 0v-0v

r9715 BKL_EN 0.4v

I2C_BKL_1_SCL ; 3.3v

I2C_BKL_1_SDA ; 3.3v

LCD_BKLT_PWM ; 0.4v

[mon2]

What is the voltage to ground of ALL_SYS_PWRGD ?

[dclass-pro]

ALL_SYS_PWRGD = 3.3V

[reformatt]

LCD_BKLT_EN and BKLT_PLT_RST_L both need to be high to pull down the gate of Q9706. You have 0V on backlight, so this FET isn't on. Should have at least PPBUS_G3H voltage on the output, even if the inverter isn't switching. BKL_EN is derived from the output of this FET.

[dclass-pro]

so do you recommend me to change Q9706?

[reformatt]

so do you recommend me to change Q9706?

Maybe try some measurements first. This isn't if in doubt, rip it out 101 here.

LCD_BKLT_EN
BKLT_PLT_RST_L
LCDBKLT_EN_DIV

When backlight is enabled from these two control signals, both parts of Q9707 turn on, and you should get 4.1V or so on the gate of Q9706 (via voltage divider R9788/R9789). If Q9707 isn't on, then the gate of Q9706 will be the same as it's drain.

[dclass-pro]

thanks guys I laughed, in fact Q9706 was damaged. I changed it and the backlight came back!!! Thanks a lot, but now I noticed that when I close the display the backlight does not turn off. the display always stays on even when closed.
What could it be?