Since very few information is available on repairing UBNT Nanostation M5 Loco ( probably the same for M2 ), i am going to post here and keep updating that post with the main kinds of failure encountered with their eventual repair
To do these repairs since the board contains big ground planes, you absolutely need to preheat it to at least 120 C° before using soldering iron or smd rework station.
Types of failure
PoE shorted, power supply led blinks as a consequence of that
This can be caused by shorted D5 diode ( look for the big black square diode on the left of the ethernet port ), replace it with another one or if you are in an hurry and willing to risk, just remove it.
Ethernet port goes only at 10 Mbit ( but usually won’t work at all even if it says that ) , or no link is detected
This is the trickiest damage, i’ve tried replacing ethernet transformer where it was evidently burned ( one winding open ), but even after that i only got from “no link” to “10Mbit” , so either other components shorted or in that case the SoC is damaged and no repair is worth to do.
The nanostation will only go into firmware recovery mode ( 4 leds blinking )
That kind of failure can be caused by remote reset NPN transistor damaged, replace or remove ( if you don’t need remote reset ) Q503 , you can find it on the right of the reset switch, beware that this kind of failure can be also caused by broken switch, so check first with a multimeter if the switch is working properly, also check that the one on the PoE injector is not broken.