ASUS p8h61-m LX3 motherboard powered on auto power off

Motherboard model: ASUS p8h61-m LX3 motherboard

Fault phenomenon: power on auto power off on the main board

Maintenance process:

A ASUS p8h61-m LX3 motherboard, the fault appears to be auto power off in less than 1 second, and it will not power on automatically. Press Switch again and auto power off again.

ASUS p8h61-m LX3 motherboard powered on auto power off Figure 1.
This can be repeated power on the reason is usually under voltage Current protection, ATX power supply VCC abnormal detection caused by Current protection, CPU temperature detection abnormal caused by Current protection.

Start up the fast detection CPU VCC has 1V or so, it can be sure that the main board VCC is basically normal, check the + 5V + 12V detection circuit, the measured 1V is also normal.

ASUS p8h61-m LX3 motherboard powered on auto power off Figure 2.
Then check the circuit of temperature detection Current protection, Asustek mainly uses lm358 chip to control, first detect the temperature detection circuit, turn on the lm358 chip 3 pin VCC close to 4V, 2 pin VCC close to 3V, 3 pin VCC higher than 2 pin VCC, 1 pin output high VCC, pq61 turn on CPU VCC, thus causing the motherboard auto power off.

ASUS p8h61-m LX3 motherboard powered on auto power off Figure 3.

ASUS p8h61-m LX3 motherboard powered on auto power off Figure 4.
The reason is found. Through Boardview, the temperature of part of CPU VCC is detected by 3 pin. There are several resistors and a double connectiondiode。

ASUS p8h61-m LX3 motherboard powered on auto power off Figure 5.

ASUS p8h61-m LX3 motherboard powered on auto power off Figure 6.

ASUS p8h61-m LX3 motherboard powered on auto power off Figure 7.

ASUS p8h61-m LX3 motherboard powered on auto power off Figure 8.
2 pin only two resistors Capacitor are not installed.

ASUS p8h61-m LX3 motherboard powered on auto power off Figure 9.

First measure this circuit, the measured pr93 is 2.2k, pr510 is 3.6k, and the drawing shows that pr510 is 15K. It is obvious that the resistance damage causes the reduction of VCC.

ASUS p8h61-m LX3 motherboard powered on auto power off Figure 10.

ASUS p8h61-m LX3 motherboard powered on auto power off Figure 11.
auto power off the 15K resistor and power on the main board again. The measured 3 pin 2.74v and 2 pin 4.487v are turned on perfectly.This is the end of troubleshooting.