ASRock Fatal1ty z77 professional motherboard has reset but does not run out of code repair

Motherboard model: ASRock Fatal1ty z77 professional motherboard

Fault phenomenon: the motherboard does not run the code when it is reset

Maintenance process:

ASRock Fatal1ty z77 professional motherboard has reset without running code repair Figure 1.

ASRock Fatal1ty z77 professional motherboard has reset without running code repair Figure 2.
A Huaqing motherboard Fatal1ty z77 professional motherboard, the main board is Previously repaired board, the line is supplemented.The fault is that the self-contained diagnostic card displays 00 after startup, and the code does not run out.Plug in the detection card and reset it.
All VCC(CPU core, VTT, vccsa, vccpll, bridge 1.05, memory 1.5) are normal,CLK is normal and reset is normal.

ASRock Fatal1ty z77 professional motherboard has reset without running code repair Figure 3.
From the sequence diagram of series 6 and 7, it can be seen that the reset is out, which means that the hard start of the motherboard is finished, and all major components are basically normal. At this time, self inspection and code running should be carried out.The specific way is that the CPU is connected to the north bridge through DMI bus, and the north bridge is connected to BIOS through SPI bus, and the CPU reads the BIOS running code.

ASRock Fatal1ty z77 professional motherboard has reset without running code repair Figure 4.
First test 16 DMI bus, in the CPU pin pin direct test,diode value are more than 500, normal!

ASRock Fatal1ty z77 professional motherboard has reset without running code repair Figure 5.
Test DMI CLK again. This is directly from the bridge to the CPU BTB connector. You can’t start the test. You can directly test diode value on BTB connector. It is normal.
Test the BIOS pin Diode value is normal, 1 pin boot with 3.3V.BIOS has also been flashed. Try to clear the BIOS and power off after one second of power on, indicating that the BIOS is basically normal.
A closer examination revealed some details:
1: The CPU is still warm and not hot when the fan is turned on for two minutes.
2: The CPU VCC is always 1.2V, and has not changed since it was started.This indicates that the CPU VCC has always been the preset VCC, and has not been adjusted according to SVID.

If you look at the timing, when the CPU sends out SVID, it needs CPU CLK to be normal, and it also needs two key signals: procpwrgd and mempwrok.These two signals are sent by Nanqiao to CPU, so they are measured immediately
Mempwrok 1.5V normal!Procpwrgd is 0V (position in the red box below)!

ASRock Fatal1ty z77 professional motherboard has reset without running code repair Figure 6.
Procpwrgd is 0V, the cause of the fault is found in the running circuit, and the procpwrgd line is scratched!Fly good line, motherboard run code booting up!This is the end of the repair.