Hi Guys,
Quick question… I was flying my quad with an APM2.5 board on it and after taking a break, I went to fire up my quad again and got the beeping motor issue. I debugged it to no power going to the board from the power module. I checked with a multimeter and found 5v at the connector to the APM, but the APM doesn’t power on.
I put a jumper on J1 and ran a wire from my BEC off a speed controller and everything is working fine. So, my question is what should I check/replace on the APM? It seems like the power module is working ok and the APM is working fine off of the BEC power. Help. 
Thanks,
KS
My post from Oct 12 th sounds the same. I looked at the APM 2 board layout and can see that the PM
feeds the board thru a fuse and diode. I think my APM must have fuse or diode out. I think I will try to feed BEC from PM to rail (same place you have your BEC from ESC) and see if the voltage and current still work. My APM still works fine…If the above case is right I still don’t know what happened to fuse or diode.
OK so I unhooked the two + leads from the PM plug and one ground wire then I wired them to a plug
that would plug into the rail using both + wires tied to + and - to ground pin. All seems to work well voltage and current still read.