Electric Skateboard Remote Control Schematic
Sounds like they could be either LDO, Transistors, MosFETS or diodes. To identify them you'll need a digital multi-meter and I would follow this simple method:




Disconnect batteries, Use diode mode to check between Pin 1 and Pin 2 (and reverse)



  If it appears to read around 0.7V in one direction then it's likely a transistor, else carry-on. 



Use diode mode to check between Pin 1 and Pin 3



  If it appears to read around 0.7V then it's likely a diode, else carry-on.



Reconnect the batteries. Measure voltage Vg between Pin 1 and Pin 2



  If absolute Vg voltage value is greater than ~2V and voltage on Pin 2 is similar to voltage on Pin 3 then it's most likely a MosFET. If voltage Vg is close to 0V and Pin 3 and Pin 2 voltage values are different, it is also likely a MosFET. Else carry-on.



Read voltage between Pin 1 and Pin 3 (V1), between Pin 2 and Pin 3 (V2)



  Is voltage V1 inferior to V2? Then it's most likely an LDO.


EDIT

To be clear, this method would only work if U3 and Q1 are still indeed functioning. If you can't determine what is what, it probably indicates malfunctioning packages. In that case, you may want to reverse engineer the circuit around them to figure out their function.