DELL 5520 notebook Won't Turn On for repair

DELL 5520 notebook Won’t Turn On for repair

Machine model: Dell 5520

No.: LA-8412P

Malfunction: Notebook no booting

Maintenance process: start with adjustable standby for 0A.

DELL 5520 notebook Won’t Turn On for repair Figure 1.

0A it’s not insulation, but it just can’t stand by. Simply disassemble the machine and then power it on. First, test the rear end of the lower insulation.VCC has it.

DELL 5520 notebook Won’t Turn On for repair Figure 2.

Continue to measure 3/5V standby power failure.

DELL 5520 notebook Won’t Turn On for repair Figure 3.

Call diode value 3V shorted to ground, and look for the 3V rear stage. Except those with resistors, there are only a few left. Finally, lock 1.8VSP VCC. After disconnecting the isolation point, 3V is not short, and all 3/5V of power-on are available.

DELL 5520 notebook Won’t Turn On for repair Figure 4.

DELL 5520 notebook Won’t Turn On for repair Figure 5.

At first, I thought it was a chip problem. I saw that there was a big Capacitor connected to the motherboard.

DELL 5520 notebook Won’t Turn On for repair Figure 6.

DELL 5520 notebook Won’t Turn On for repair Figure 7.

After being removed,Measuring diode value no longer breaks down Short circuit,Capacitor breaks down again, and the insulation is connected, and the connecting screen lights up normally.

DELL 5520 notebook Won’t Turn On for repair Figure 8.

PS: When the standby circuit of this machine is normal, it is only a dozen to the ground. The back end of Inductor was measured with an oscilloscope, and 5V lasted for a while before it fell off, and 3V fell off. It was judged to be a 3V problem!