A1989 EMC3214, No display backlight

The user said that the system was working fine and suddenly one day its backlight was missing. I can see the laptop has been already opened by someone. Even the display assembly also opened. I have an A1706 display spare for testing, Will it work?. I don't have an A1989 working display to confirm the failure.
I couldn't find the backlight flex cable broken physically.
Is there a way I can confirm the issue, I don't know whether it is the problem with the display or motherboard?
I can see the display image if I use a mobile flash light.
 

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What is the exact backlight voltage (LCD connected)?

If you want to test with other screen, be sure the video connector has the same layout.
 

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Schematic/boardview available, probably already posted on the forum.
Post the voltage at C8466 (or other cap in the same row), with machine on and lid opened.
 
Yes, Confirmed that it is not a displayed problem, Even with the a1706 display it has the same behavior, No backlight. Either the boost circuitry not working or it is the flex cable between the display and Motherboard?
 

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If you catched 12V at backlight output, means that is trying to start at least.
Check all traces and solders in backlight cicuitry.
Change the small video cable from MLB; need to discard it.
 
The feedback resistor was corroted , Now backlight is working .
I have also seen L8504 was burned , Since the U5610 not equipped I have just removed that inductor, Do you know whats the purpose of this circuitry ?
 
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