A1502 No Backlight, No Keyboard Backlight

[riyadh144]

Hi,
I am usually not a technician, but work as an Electrical Engineer, and I do believe I know my way around a soldering iron and a DMM.

Anyway I am here to get some help from experts.

I have a A1502 13" early 2015 model 820-4924-A

Symptoms

1. I can see output on the screen when I shine some light on it, and it outputs to the monitor.
2. The board is very clean, no signs of any corrosion
3. I am getting voltage on enable pin for U7700 not getting voltage on pwm_keyb.
4. There is no short on the power output to the display, I believe the cable and the connector are fine, unless one of the other pins are shorted.
5. Q7700 has no output the gate and source are high.
6. None of the fuses are blown, I have checked most of the resistors they all seem fine.
7. Replaced U7700, it wasn't at fault.

Now the first thing I would like to know how do you power up the device without plugging in the battery as it is making my life hard plugging in the battery to power up and then removing it after it is on.

Please give me thy knowledge, I have searched around the website, checked all what was suggested, everything seemed fine.
I have read Louis's guide, it is pretty good, but still didn't help my stupid self figure this out.

Also you guys are doing great work helping out the community standing for the corrupt man.

 

[2informaticos]

First of all, welcome to the forum!

U7700 controls both LCD and keyboard backlight.
Try 2-3 times PRAM reset as first step.
Disconnect the webcam, to prevent an ALS issue and test the machine again.

This board should start automatically when charger is plugged in.
However, I remember few members complained that board didn't turn on without battery; never faced myself with this issue.
You can use R5115/16 pads instead of power button.

 

[riyadh144]

I just tried resetting PRAM a few times, sadly that didn't do it.
Sorry for the noob question but to reset the pram I followed this guide? Is that satisfactory?

Reset NVRAM on your Mac - Apple Support

If one or more settings stored in NVRAM don't work as expected on an Intel-based Mac, resetting NVRAM might help.

support.apple.com

Thanks for the quick response

 

[2informaticos]

Did you test the machine without webcam connected?

 

[riyadh144]

Yes I do believe I have the right connector disconnected.

I should do the PRAM reset after disconnecting the camera right?

 

[riyadh144]

Also I just ran a diagnostic test, and with shining flash light on it said that there might be a problem with the camera which is expected
But it isn't mentioning any problem with the display.

I removed the display connector and did the test again while connected to external display, it said there might be a problem with the display code VFD001

 

[2informaticos]

Display error must be due to missing it on the test.

Did you try known good compatible LCD assembly?

 

[riyadh144]

I don't have any other displays sadly. So that won't be easy.

 

[2informaticos]

LCD backlight is controlled through I2C bus, from LCD itself.
LCD receives EDP_BKLT_PWM from PCH and send I2C information to U7700.
Check at least if you get some voltage at EDP_BKLT_PWM; DC voltmeter should be able to show something.