It is the problem of judging the power supply chip and its peripheral accessory components. Brush the solder paste, and re-solder the capacitors and resistors around the chip to be processed with an air gun. After cooling, the bare board is electrified, and the current goes up to 0.5+ and then goes up to 0.8+~1.0+ after a short stay. Plug in the screen and test the lighting machine.
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.
Judge whether it is the standby chip or the voltage is pulled down or leaked, and find the same model as the 5V standby chip PU18V00 chip from the new drawing. The problem is still this 11-pin problem. The resistance of 1 pin connection is 47K, and 1.8V normally appears after replacement.
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.
