Gigabyte GA-B85M-D2V does not trigger repair

Gigabyte GA-B85M-D2V does not trigger, IO is broken, replace one on the pallet, and repair the fault.

Machine model: Gigabyte GA-B85M-D2V

Fault phenomenon: no triggering

Maintenance process: The colleague took a motherboard and asked for help. He said that the bridge might be broken. Let me see if I can save it. After getting the mainboard, pressing the switch did not respond. The 2.56V of the measuring switch pin was obviously abnormal. Continue to measure the 1117 5V produced by the standby 3.3V, and the normal output 2.56V was normal. It should be 3.3V, but the 1117 could not be broken.

It is still the same when removing one from the material plate and replacing it with another, that is, there is a problem with the rear stage. Disconnect the parts that are in contact with the standby 3.3V one by one. In addition to the bridge, 2.56V is still the same for half a day. I have decided that the bridge is broken, but I still don’t give up. Connect the voltage regulator 3.3V to the 1117’s 3.3 output pin, and then measure the power pin 0.25V. However, the measurement of R172’s 3.3V end and 0.25 end is completely different from the previous one, which means that the bridge is OK. Then why is the 1117’s output not 3.3V? When the power is off, replace the two power banks NR176 NR180 connected to the 1117 with 2PIN. When the power is on, the output is 3.3V, but the switch pin is still 0.25V. Continue to remove the IO, and the switch pin 3.3V is normal, The IO is broken, the material plate is replaced, and the boot is triggered. It is repaired here.