GA-B75M-HD3 REV: 1.0 triggers instant power loss repair

Gigabyte b75m-hd3 Rev: 1.0 switch instantly enguishes auto power off, removes q54, solves the problem, lights up normally, and the maintenance is completed.

Machine plate No: GA-B75M-HD3 REV: 1.0

Fault phenomenon: switch 0.3-0.5 seconds auto power off

Fault description: switch is instantly enguished, and switch cannot be stopped.auto power off speed is a little slower than that of CPU Short circuit, and it is much faster than VIN to detect auto power off fault.auto power off speed is similar to that of Jijia 6x7x VVT VCC fault auto power off, and multimeter cannot be measured.

GA-B75M-HD3 REV: 1.0 triggers instant power loss repair Figure 1.

Maintenance process: for this auto power off speed, first measure VTT, because auto power off is too fast, and there is no oscilloscope, but pull out 4Pin auto power off, it is roughly judged that it is not VTT fault.Vin detection is normal, pull down the speed of the apwrok auto power off. After 10 minutes of touching, nothing is found. According to the old idea, it must be repeated again and again.

First think about how to repair it. I’m going to test it twice

Scan the small MOSFET of the whole board in standby mode.
switch auto power off and then scan again to see if there is any abnormal difference before and after comparison.
However, it is not as troublesome as you imagine. When you scan from bottom to top for a few minutes, the fault will come out.

GA-B75M-HD3 REV: 1.0 triggers instant power loss repair Figure 2.

Scan to q54 this MOSFET level D 1.4V, very rare this VCC, open the drawing point to see.

GA-B75M-HD3 REV: 1.0 triggers instant power loss repair Figure 3.

Q54 is a good standby signal of rsmrst, 1.4V is definitely abnormal, and it is normal at 3.3V

GA-B75M-HD3 REV: 1.0 triggers instant power loss repair Figure 4.

The 1.4V VCC is abnormal, but it can still be switch, so this is the normal thinking.Standby good signal will be ignored, directly remove the q54, do not rsmrst recovery 3.3V, after switch no instant auto power off fault.Remove the q54, solve the problem, light up normally, and finish the maintenance.