The usus a42j notebook is not powered on for repair

The usus a42j notebook is not powered on for repair

Machine model: usus a42j
Fault phenomenon: notebook does not turn on.
Maintenance process:

ASUS a42j notebook no booting.

The usus a42j notebook is not powered on for repair Figure1.

Peer said no power on, removed the battery directly connected to DC power supply 0.001a.

The usus a42j notebook is not powered on for repair Figure2.

The standby function is too low to achieve the deep sleep function?Press Switch several times without any change,switch cannot.Remove the machine, when removing the keyboard found a large area of water damage traces.

The usus a42j notebook is not powered on for repair Figure3.

Remove the motherboard and look at the eye plate number k42jc R22. When the forum started work at the next point, I used to look at the maintenance traces first. There was no obvious lack of parts after several passive visits.Another value, each big Inductor common point found two faults, common point 6, 3V Inductor 3, it seems that Short circuit, all this, there is no large current, this if switch can be strange.

The usus a42j notebook is not powered on for repair Figure4.

The usus a42j notebook is not powered on for repair Figure5.

The common point has a value of 6, which indicates that it is not Capacitor. It is likely that the field tube is broken down. It is found that the unique PWM upper tube is broken down. The Inductor of the display card is not short. I hope it is still alive. Replace a pair of field transistors, and the common point is not Short circuit.

The usus a42j notebook is not powered on for repair Figure6.

When 3V isolation point is disconnected, the back stage is short.Current heating test is found to be a network card problem. After the 3V Measuring diode value is disassembled, it is normal.

The usus a42j notebook is not powered on for repair Figure7.

The usus a42j notebook is not powered on for repair Figure8.

Replace the chip again Measuring diode value is OK.

The usus a42j notebook is not powered on for repair Figure9.

Once again,Measuring diode value does not have Short circuit and has not been isolated by Current protection when powered on. Find the charging chip mb39a1. The data manual introduces the definition of pin, but it does not give the threshold value and does not drive pin. It should be p-tube isolation.

The usus a42j notebook is not powered on for repair Figure10.

Checking Boardview, it was found that the D pole of the isolation tube had 19v, G pole 0V and S pole 0V, which was not connected at all. It should pass through the body normallydiodeCome on,VCC good partial pressure control on, tube broken?

The usus a42j notebook is not powered on for repair Figure11.

Measure the normal value once. How is this the measurement value of N tube? Look at the numberP1203BVIt turns out to be n tube. No wonder it can’t be connected.

The usus a42j notebook is not powered on for repair Figure12.

After changing a p tube to power on again, just listen to DC power supply bang, 5A large current, and quickly turn off the power. At this time, there was a smell of scorching. It was found that it was a 3 pin chip that had been repaired before.Check is a Schottky diode, according to Boardview should be to PWM reference VCC.

The usus a42j notebook is not powered on for repair Figure13.

After measuring, the common point becomes 6 again. After measuring, the upper tube of the video card is broken down again.Remove the upper and lower tubes and three pin chips, not Short circuit, try to power on for a while, already can power on 0.3A, except for the graphics card, each Inductor VCC are normal, install u and memory, look at the current should be turned on, connect the screen, it is really on.

The usus a42j notebook is not powered on for repair Figure14.

The set display has been working normally. After measuring the small parts around the PWM, I feel that there is no problem. The teacher has taught me before, repeatedly burning the field tube, first changing the chip and booting Capacitor. ASUS QFN type chip is the most difficult to weld. Thanks to the pressure of the captain and teacher Alin, the power supply has been normal after welding.Take a screen test,The network card has been able to identify the normal Internet access.

The usus a42j notebook is not powered on for repair Figure15.

The usus a42j notebook is not powered on for repair Figure16.
After a look at the manager, Duxian is working normally.This is the end of the repair.There are a lot of fault points. There are also pits left by my family carelessly. The maintenance time is a little long.