Hi John @John_Ninja
Thanks for the diagram
Are you using a 3S or 4S battery? if 3S (11.1v nominal) then do not use the 12v BEC output, it will only give you about 10v and the linear regulator on the PDB will not provide any supply suppression.
extract from MATEK site >>>
Most importantly, Use a digital voltmeter to check voltage on the 5v pad and GND. I'm suspecting you have a faulty board and it's been putting full battery voltage to the FC ESC 5v line
BUT I'm going to question why you are powering the FC from 5v on the ESC connections ? you ought to be connecting FC to the Vbatt connections from the PDB (VCC & GND)
This will power the FC correctly and you will also have the LiPo battery voltage reported for telemetry / OSD if/when you need that very useful feature.
Let us know how you get on