It was suspected that the resistor was leaking. The R2014 resistor was tested by 10K and 100K in turn. The voltage of HDP was different, which ruled out the problem of CPU. It was caused by the leakage of R4521 resistor. Remove the motherboard, wash R2014 with washing water, and the boot is normal.
0.65mA should be that the CPU didn't come up. After checking, it was found that the two capacitors behind the CPU were broken. Replace two 330U capacitors, make sure that there is no error in power-on test, and the current goes up to 1.26. Turn off the machine, connect the screen, and turn on the machine.
The measured VR_EN of the power supply chip only fluctuates between 2.9V and 3.2V, and it is obvious that there is a problem along the way. It is measured that the PG signal of memory power supply of 2 pins is abnormal; After the small tube is replaced, the power will not be cut off, and the voltage will return to normal.
After checking, there is an indicator light on the inserted charger, and there is no boot response when the power-on key is pressed, but the indicator light will go out when the power-on key is pressed, which may trigger protection due to local short circuit. It is found that many capacitors are short-circuited. After removing the short-circuited capacitors, test the other capacitors to ensure that they are not short-circuited. After commissioning, 3.3V returns to normal.
The standby chip is hot, and the short circuit of EC causes LDO 3.3 to be pulled low; Judging from the problem on the EC side, I found that there was a needle attached to 5V, which caused the EC to burn when it was powered on. Pins are broken, and then an EC is changed. The boot is normal, and the fault is eliminated.
First plug in the USB mouse for testing, and the visual mouse light is not on, which is due to the lack of USB+5V power supply. After the flying line, USB_P1 on the small board is connected to USB_P6；; USB_P2 to USB_P4. The test can identify the use of USB devices. Just give up the function of the camera, but don't have to change the CPU at a high price.
Haier's T90-T notebook doesn't start up, and it is preliminarily judged that there is power supply and it can't work normally. The actual measurement shows that SLP_S3# has no voltage. Finally, a brand-new original South Bridge chip was replaced, and ME was configured. The test of the machine entering the system was all normal.
Lenovo ThinkPad L450 notebook can't be charged. After measuring the motherboard, it is found that 20V is only 19.4V The investigation focuses on these two protective isolation tubes.
Alien Alienware M18 R3 computer screen suddenly restarts with a black screen, and the cpu frequency is locked at 0.78GHZ. Immediately put on four 470uF tantalum capacitors, and the fault was solved.
