Lenovo Y400 notebook press switch unresponsive repair

Lenovo Y400 notebook press switch unresponsive repair

Lenovo Y400 notebook didn’t respond when pressing the switch. When the trigger current goes up for a while, the power will be turned off, then the original BIOS will be brushed back, and the machine will be turned on directly.

[Machine model] Lenovo Y400 notebook

[motherboard version number] NM-A141 REV1.0

[Fault phenomenon] The notebook doesn’t respond when pressing the switch.

[maintenance process]

Upon receipt of Lenovo Y400 notebook, the customer described that the computer can be turned on before, and sometimes it will not be triggered. This time, it will not be turned on directly. The power-on non-triggering current is about 0.03.

When the machine is disassembled, the bare board current jumps back and forth around 0.15-0.2, and there is no response when the switch is pressed. Lenovo’s machine has been repaired a lot, and no obvious short circuit has been found in the common points of power outage and the major inductors.

The measuring common point voltage of 19.8V is normal, the G pole voltage of the upper and lower tubes for measuring protection isolation is about 7 V, and the standby voltages of 3 and 3,5 V are also normal.

So we began to measure the working conditions of ec IT8580e. The voltage of ec pin 74 +3VALW_EC was 3.3 V, that of pin 18 +3VALW_R was 3.3 V, and that of LID_SW# was 3.3V. The voltage of 20-pin ACIN is only 2.6 V, which is abnormal. It’s also a detour from here.

Lenovo Y400 notebook press switch does not respond to maintenance Figure 1

ACIN voltage is divided by pr297 and pr299, pulled up by pr298, and controlled by pq45b. The measured voltage of BQ24737_VDD is 6 V, the G-pole ACPRN 0 V of pq45b is normal, and PACIN3.3 V generated by voltage division is normal.

Pull-up is normal, it is only 2.6 V through the resistor pr298 to ec, and there is only one capacitor in the middle. When the capacitor is disassembled, the voltage is still the same. The measurement of ec to pr298 was not disconnected, and I began to suspect ec. There is no problem in measuring the switching voltage, so the ec is dried directly. Measuring acin voltage is normal.

Lenovo Y400 notebook press switch does not respond to maintenance Figure 2

Look around the forum for ideas, change the EC, and the current jumps back and forth around 0.08 to 0.20, so as to measure acin or 2.6.

Lenovo Y400 notebook press switch does not respond to maintenance Figure 3

The ec has been dried again, and the measured ACIN is 3.3 V again.

Lenovo Y400 notebook press switch does not respond to maintenance Figure 4

Maybe it’s not the ec, because it’s impossible for both ECs to have the same voltage. Dry the original ec back again. Change the isolation chip, change the standby chip, change the filter capacitor of standby 3,5 V, change the filter capacitor of standby linear voltage, and brush the BIOS, which is still the same. Actually, it’s not the step to read the BIOS.

Until I saw the post, I started measuring the standby voltage again. The linear voltage of 3,5 V is normal and stable.

Lenovo Y400 notebook press switch does not respond to maintenance Figure 5

When I measured the standby 5 V, I found that there was a slight jump in 5 V, just a little, and I didn’t notice it at all. So the upper and lower pipes of 5 V were changed, and ACIN was measured to be 3.27 V. When the trigger current goes up for a while, the power will be turned off, then the original BIOS will be brushed back, and the machine will be turned on directly.