Aspire V5-471(11309-2) Turns On Occasionally

Laptop Model : Aspire V5-471

Motherboard Number 11309-2

Fault :Turns On Occasionally. 

Repair Process :

           The board plug-in standby mode is a bit large, and the screen can be displayed even when you turn it on by pressing the switch, but it won't turn on when you turn it off and on again. 

After a while, the bare board can be plugged in and it can be turned on again. The bridge is a little hot to touch and the temperature is abnormal. There is no 3V and 5V voltage when not turned on. After pressing the switch, you can test that 3V and 5V come out and then fall off, and they keep going back and forth.

The oscilloscope showed no problem when playing the waveform, and the RSMRST# also came out and then fell off. The standby chip is also switching on when it is turned on.

Because it can be turned on occasionally, I directly pulled the on of the standby chip low to allow 3V and 5V to be generated directly. But it still didn't work when I turned on the Laptop again. I tested that pin 117 of U2701 is always 0V.

This is definitely not normal. After flashing the BIOS, it is still the same. The power supply and reset are normal. If I directly replace the EC, the result is still the same problem. 

After looking around the forum, some experts said that the temperature control U2801 may cause this problem, and even if it is removed directly, the problem remains. 

Check to see if it's a problem with the bridge? Pulling down the EC pin 117 resulted in no jump. The RTC condition was checked, the DSW voltage was checked, and the BATLOW was normal.

I had no choice but to replace the bridge directly, but the result was still the same fault.I still have confidence in the BGA, but I have no direction. I started to doubt the standby chip.

Anyway, it is fast to replace, but it is still useless after replacing it. However, after replacing it this time, I can no longer turn it on occasionally. Now the problem seems to have become bigger. 

I took a day off and took another look. I started testing the EC conditions from the beginning and found that the ACIN was wrong.

When I started to check the Laptop, I tested it and it was normal. But now it is not normal. I directly tested the isolation tube and found that PU4001 was not fully connected.

This discovery makes me feel baffled. How come the protection and isolation are not fully connected when I can occasionally turn on the computer? I really don’t know if this is an original fault. Let’s deal with it first! There is a problem with the resistor and capacitor of pin 20 of PU4003. 

After replacing it directly and then powering it on, the standby time became smaller. The fault was eliminated and the repair was completed. I don't understand the original fault of this Laptop or what the bad things are.

I can only judge the cause of the problem by looking at it. I think incomplete conduction of protective isolation should not cause this phenomenon.

Happy Repairing !!