it looks like you count the pin wrong of the connector on the power supply board based on the schematic that is why you thing they are connected to ground.
Power supply connector ....... Main board connector p801
1 m/s = PIN 11 which is the Analog DIMMING CONTROL
2 dim = PIN 10 which is the PWM Dimming control
3 on = PIN 9 which is for inverter BL ON/OFF. You are not getting this signal to turn on the backlights.
4 olp = PIN 8 connected to GND
5 gnd = PIN 7 connected to GND
6 5.2v = PIN 6
7 5.2v = PIN 5
8 gnd = PIN 4 connected to GND
9 gnd = PIN 3 connected to GND
10 15v = PIN 2 15V SUPPLY
11 15v = PIN 1 15V SUPPLY
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