By looking at the same circuit from point to point, it is found that the capacitor corrosion is severe near the circuit corroded by water. Remove the CD3205 chip near the corroded circuit, and there is slight corrosion under the pin. Clean up the capacitors and resistors with corrosion around them, and stick the CD3205 chip again. It is normal to boost the voltage by 20V.
Apple MacBook Air A2159 notebook can’t be started for repair. The burning machine found that the memory was hot, but it was short-circuited when the memory was removed. It is estimated that the CPU was burnt out, so it was…
Confirm that T2 may have a fault, check that T2 is not short-circuited, and trace that T2 external BIOS waveform is normal. Rom has started to work, and T2 has also turned on the CD3215 I2C bus with 1.8v waveform and voltage. In this case, directly replace the CD3215 chip, and both of them can be changed together, which can boost the voltage, boot normally, and turn on the machine perfectly.
Dismantling the machine, it was found that the chip near the screen interface of the main board was wet and corroded. Dismantling the chip, it was found that the bonding pad had been disconnected. After cleaning the pad with flying wire and washing board water, install the chip, and check the drawing to know that U8300 is the chip that supplies power to the screen. After processing, the boot test has been shown.
The memory slot is corroded, and both sides of the memory are corroded. Especially, the memory chip on the right side of the memory is burnt directly. First, the memory slot is replenished, and then the screen line interface is processed. The other side of the screen line is also burnt. Scrape it with a knife, patch a line, and then plug it back in. The boot current runs directly, and the machine is turned on.
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.