Its your power system not being upto the job
so i need to replace the power module?
There are many factors, like maybe your battery didnt have a high enuff C rating or perhaps it was low. If the motors suck too much, voltage will drop and you could get a brown out because the voltage drops to low, and the capacitors along the way got completely drained and didnt have enuff in reserve.
Brownout is lower-than-spec-voltage state at which a cicrcuit cannot mainain normal operation, an microcontroller/processor usualy have a internal brownout detection, which pulls down reset while voltage is below minimum - to ensure proper start, and not unpredictable corruption/crash.
If you see the log suddently stop, and maybe then a new log start (reboot) even before hitting ground - that can be a brownout.
in short: your +5v is not reliable if that happens - or there was a overload.
yup, sometimes you can spot it looking at the Vcc log in the log files if your flight Arducopter based controller supports it (I.e APM and I assume Pixhawk, VR Microbrain doesn't). Look for voltage dips or a generally low voltage.
Although the auto log analysis tool will show a brown out error if your power system is fine but a cable got yanked/Failed, as the log file will be truncated (not complete).