Lenovo Z41-70(LA-C281P)Does Not Turned On

Laptop Model: Lenovo Z41-70.

Board Number : LA-C281P

Fault : Does Not Turned On

Repair Process:

 

When plugged in, there is a very small standby current that keeps jumping around. No, this should be the standby voltage short circuit protection. 

There were no drawings at the time, so I thought that since the problem was with the standby voltage output circuit, wouldn't it be better to just fix the problem with the standby voltage? There is no drawing, and I don’t know where the standby voltage is generated, but I know that the switch that turns on the power must have a standby voltage.

Run the switch wiring and find a pull-up resistor. When measuring the pull-up resistor, the voltage keeps jumping from 1 .It keeps jumping from a few V to 0V.

 

At that time, I only thought that there should be a problem with the 3V standby voltage, but the process of running the wires proved that sometimes the notebook circuit board cannot run the wires.

 

When it reaches the via hole, there are no wires on the back. In many cases, there are still It requires drawings to solve. I'm so hot that I won't run if I can't run the line. Let's use electric current to burn the machine! 

During the burning process, it was found that the 3V standby chip was located near the memory slot. The RI5LG chip was slightly hot, so I arbitrarily thought that the chip was broken, so I bought the chip and replaced it.

The chip came back and was replaced, but the fault remained and it has not been repaired. Was my thinking wrong from the beginning? Start reflecting. Suddenly, I realized that before buying a chip, I should check whether the chip meets the working conditions! I downloaded the drawings from the forum and took a look.

The input of the measurement chip also jumped in voltage from 1-2V, which means that the voltage at the common point did not come out. When the power was turned off, the resistance at the common point was only 8-11. It is obvious that the common point is short-circuited and the real cause is finally found.

 

　　I simply checked that there was no obvious short circuit in the protective isolation circuit. It should be a problem with the downstream stage. I connected a wire to burn the Laptop.

I touched the whole board and finally found the hot place, which is the 5V standby voltage next to the 3V standby voltage. , found that a cracked filter capacitor was very hot. 

It's really hard to find when it's hidden next to a large capacitor. It seems that the appearance inspection before repair is very important. If you have to be careful and discerning enough, many problems can be found.

This time, I will be more cautious and remove the cracked bad capacitor, and re-check the resistance of the common point. Now it is more than 400, and it should be back to normal.

The plug-in standby current is more than 0.01, the common point is 19V, and the standby voltage is 19V. 3V5V are all normal. Let’s look at the size of the capacitor in the drawing. It has 0805 specifications and is 10U. I didn’t have a 10U capacitor on hand, so I installed two 5U capacitors.

 

　　Press the switch, and the current reaches 0.4 and then stops. It should be the memory. I removed the memory, wiped it, installed it and powered it on again. This time, the current easily increased to 1.4 amps, the display lighted up, and the fault was repaired.

Happy Repairing !!