Emb-6011 mainboard power on without display repair

Board number: EMB-6011(H81 chipset)
Fault phenomenon: no display when the machine is turned on.
Maintenance process:
This board is Previously repaired, and the motherboard has been PCH.

Emb-6011 mainboard power on without display repair Figure 1.

Emb-6011 mainboard power on without display repair Figure 2.

There is no problem in appearance inspection, and there is no abnormality in the ground value by typing VCC. The CPU and memory are installed, and there is no display after power-on. Measuring memory VCC 1.33V

Emb-6011 mainboard power on without display repair Figure 3.

VCC 1.05V bridge

Emb-6011 mainboard power on without display repair Figure 4.

According to the drawing, buses VCC and IO VCC are converted from bridge VCC through resistance, and the actual measurement is normal.

Emb-6011 mainboard power on without display repair Figure 5.

When CPU VCC is measured, it is found that there is no CPU VCC, which is H81 motherboard, according to the 8 series timing.

Emb-6011 mainboard power on without display repair Figure 6.

When all VCC are normal, CPU VCC will be generated, and when it is normal, SYS_PWROK will be generated. Moreover, SYS_PWROK in VCC comes from the PG phase of SLP_S3# and CPU VCC, and the measured value is 0 V.

Emb-6011 mainboard power on without display repair Figure 7.

Is to turn back to repair CPU VCC, this board CPU VCC chip NCP81102M.

Emb-6011 mainboard power on without display repair Figure 8.

According to the drawing, 2PIN is chip VCC 5V, and the measured 4.82V is normal. 2 pin 2V is pulled up, and the measured value is normal. 1 pin is turned on by ALL_SYS_PWRGD and SLP_S3#, and the measured value of 3.3V is also normal.

Emb-6011 mainboard power on without display repair Figure 9.

Measure the wave-free type of the upper tube G with an oscilloscope, indicating that the chip is not working. After the chip is replaced, the power-on failure remains the same. Measuring chip working conditions, the measuring chip is turned on, and the ground diode value is only 30, which is abnormal.

Emb-6011 mainboard power on without display repair Figure 10.

The CPU of this board has 4-phase VCC, four such small chips in total, and the resistors are disconnected one by one according to the drawing.

Emb-6011 mainboard power on without display repair Figure 11.

When it is disconnected to PR111, the diode value of other grounding points returns to normal. Measure whether the diode value of PU9 terminal is more than 30. After replacement and measurement, all ground values have recovered to more than 400.

After changing the chip, power on, CPU VCC has come out, and the waveform diagram of the front end of CPU VCC.