Hi everyone, I have this peculiar back-light issue.The MacBook came to me with a broken L7710, and after replacing, it powers on without back-light, but when I close and open the Lid or when I pass a magnet around the HALL Sensor area, the back-light appears.I have also noticed that when I pass the magnet around the Sensor whilst the screen is on, it does not go off even though it's supposed to. I have reset PRAM but that has not helped and there is no sign of liquid damage anywhere.I want to know if someone has come across this issue before and whether its a hardware or firmware issue.Thanks in advance.

L7710 delivered with the same value? This is critical.
Check the entire lighting circuit from the circuit. It may be necessary to replace the U7700. I think the problem is hardware.

The macbook was taken away but another board came with the same issue and these are the voltages on screen connector (J8300) when powered on with image on screen and no backlight;
PPVOUT_S0_LCDBKLT -51.8v
I2C_BKLT_SCL - 5.36v (oscilloscope activity)
I2C_BKLT_SDA - 5.36v (oscilloscope activity)
PP3V3_S0_EDR - 3.3v
SMBUS_SMC_0_S0_SCL - 3.3v (no oscilloscope activity)
SMBUS_SMC_0_S0_SDA - 3.3v (no oscilloscope activity)
EDP_BKLT_PWM - 3.6v (oscillocope activity)
LCD_HPD_CONN - 2.48v
LCD_IRQ_L - 3.28v
PP5VR3V3_SW_LCD - 5.28v

SMC_LID is also 3.3v with backlight off

When I close the screen or bring a magnet near the Hall Sensor,the backlight comes on.Anytime the backlight goes off, the screen has to be closed and opened before the backlight comes on.Could this be an SMC issue?. I will be grateful if someone can point out which other signals control backlight switching apart from the hall sensor.

Make sure the screen is compatible with the model.

https://webcache.googleusercontent.com/ ... backlight+

(using a webcache link since their site is not working properly right now)

Thanks so much for the info. I somehow suspected it because there was a tamper proof sticker at the bottom of the screen, which suggested that the screen might have been replaced (and obviously with the wrong one). Unfortunately i never got a similar laptop to check the motherboard with and the customer has come for it.Thanks once again..