Lenovo Xiaoxin AIR13IKB Pro notebook no booting repair

Machine model: Lenovo Xiaoxin AIR13IKB Pro

Fault phenomenon: notebook no booting

Maintenance process: other peers have contacted but failed to repair. Send it to me for the third repair.If the repair is not good, the peer intends to deal with it as spare parts.

Lenovo Xiaoxin AIR13IKB Pro notebook no booting repair Figure 1.

There is no CMOS battery after the machine is disassembled. A device is provided to prevent the RTC circuit from causing other faults.This machine must be equipped with batteries to press Switch switch. There is no verification. I plug in the battery from the beginning to the end.

Lenovo Xiaoxin AIR13IKB Pro notebook no booting repair Figure 2.

After the disassembly, there was no obvious trace of maintenance. The original fault was not passive. The standby current of 0.004a was inserted into the regulated power supply. The standby current was too large, and there was no response by pressing Switch. All the large Inductor diode value were normal. Next, look for the drawing. The mainboard version number is la-e011p.

Lenovo Xiaoxin AIR13IKB Pro notebook no booting repair Figure 3.

To remind you here, because no power on directly chooses to find the standby condition of EC, the 3.5V of this book should be generated by pressing Switch. After finding the standby VCC pin 67 of EC, it is found that there is no VCC.

Lenovo Xiaoxin AIR13IKB Pro notebook no booting repair Figure 4.

After tracing LDO VCC from 3V circuit, it is found that B +VCC is not generated in PWM working condition sequence!

Lenovo Xiaoxin AIR13IKB Pro notebook no booting repair Figure 5.

According to this fault, it starts to return to the origin: the charging circuit, the charging chip model is isl95520ahrz, here we can see that the AcIn dcin conditions must be met, and acok cannot be low.

AcIn measured 3.2V, dcin 19v, acok 3V,or so are normal. You may think that this is normal at this time. There is nothing wrong with it. According to the common point of the actual circuit,VCC is also normal. You think it is very right. Then how to adjust it?You can see from schematic.

Lenovo Xiaoxin AIR13IKB Pro notebook no booting repair Figure 6.

Because the PWM generation circuit of 3v5v is B +, so to find B +, there is no VCC in the actual measurement of B. the problem is found.So why didn’t it happen?Either there is a problem with the composite field transistor below, or there is a problem with the chip.In order to maintain the principle of changing small and not changing large, the actual motherboard here are two MOSFET, not composite.

Lenovo Xiaoxin AIR13IKB Pro notebook no booting repair Figure 7.

But the principle is the same, controlled by the charging chip. I hit the diode value of the first MOSFET and found that there was only 200 or so, which was definitely wrong. I found a normal MOS diode value 500 or so and replaced it. I thought it would be a second kill.

Therefore, the standby current of the regulated power supply becomes 0.001a normal. Press Switch,switch, and the current runs to 0.8.or so lights up once, and auto power off directly. The standby current of stabilized power supply is 0.1A or so. Is BIOS broken?