DELL 5750 No Display Repair

 

Machine Model: DELL 5450

Board Number: DAJW8CMB8E1

Fault: No Display

 

Maintenance Process:

 

It is detected that the notebook does not display when it is turned on. It can occasionally display but the screen is still dark. It is judged that the screen cable is broken. After replacing the screen cable, the screen flashes (dark screen - bright screen alternately).

　　The screen flashes when the motherboard screen cable interface is pressed with a finger. When testing the dark screen, the LED-BL 19V is normal and the backlight turn-on signal LCD_PWM_IN 0V. The fault point should be here. When the screen flashes, the LCD_PWM_IN 0-1.7V jumps.

Look for LCD_PWM_IN to the composite diode.

    There is no disconnection in the test, and the LCD PWM EC is 0V both bright and dark.

    When flashing alternately, the EDP_PWM_OUT voltage changes from 0 to 1.7. Find out that EDP_PWM_OUT is sent by pin 12 of PS8620/23. There is no disconnection during the test.

    At this point, it can be basically confirmed that the PS8620/23 or EC or bridge is faulty. Considering that there are traces of the pot being dropped on the machine casing, it is estimated that the bridge is probably more likely. In the end, I decided to be a flyer and find the screen power supply of 3.3V.

    Connect a 10K resistor flying wire in series to pin 3 of the D17 diode. After booting, there will be a PWM start signal, as shown in the picture above:

Happy Repairing !