DELL 5520 Laptop That Does Not Turn On

Laptop Model: Dell 5520

Board Number: LA-8412P

Symptom: Laptop does not turn on

　　

Maintenance process:

 First set the adjustable standby 0A

0A is not guaranteed, but it just won't come out in standby mode. I simply disassembled the device and then powered it on. I first tested the isolated rear end and found that the voltage was there.

Continue to test the 3/5V standby power level.

　　Short-circuit the resistor value 3V to ground, find a 3V power stage, except for the ones with resistors, there are only a few left, and finally lock the 1.8VSP power supply. After disconnecting the isolation point, the 3V voltage is not short, and 3/5V is present after powering on.

At first I thought it was a chip problem, but I saw a large capacitor connected to the motherboard.

After removing it and setting the value again, there is no short circuit anymore, the capacitor breaks down, the insulation is connected, and the screen lights up normally.

PS: When the standby circuit of this machine is normal, the ground connection is only a dozen or so. I used an oscilloscope to measure the back end of the inductor. I found that 5V lasted for a while before it dropped, and 3V dropped immediately. It was determined that it was a 3V problem!