Hi I I accidently connected my A20-OLinuXino-Lime2 with 12v dc power.. So I unplugged power when I noticed (it took 1 min or less). After that, I plugged with 5v dc power but board shows only power red led.. and seems not working.. How can I find out if board is burned or not?
I am using A20-OLinuXino-LIME2-e4GB for freedombox
I've done this multiple times. The board is damaged for sure. What exactly got damaged is hard to tell. This would require measuring most of the components on the way of the current starting from the power jack. Quite likely the AXP209 got damaged since its absolute maximum is 11V and there is nothing between the power jack and the AXP209. However, it is very likely that other components got damaged too.
We did same mistake, and found problem.
Solution is, remove Diode D3 i.e. SMBJ6.0A and it will work.
(Later replace the diode D3 with new one.)
Use only 5v power supply.
C174 probably suffered
If the diode D4 has been short-circuited, the pcb may not be destroyed.
This can be checked by supplying the pcb with a voltage generator (between 4 and 5V) connected to the jack with a resistance of about 15/30 ohm (about 2 W) in series.
If the 5VEXT/GND voltage is close to 0 V we can expect the circuits not destroyed and investigate further.