Radio Control Helecopter.

This had been sat negelected for a long time (over a year !)! Cheap radio control helecopters have come on a bit since this model was given to me for repair (and forgotton about !) but I decided to get it done anyway.

Only one of its twin rotors would spin.

The two motors were wired to a dual n channel mosfet package, only one motor spinning tended to indicate one dead mosfet ! It was a FDS8926A (8 pin package just next the red wire closest to the bottom of the pic) , a replacement chip was sourced for <£1 and fitted, the original chip was definitely dead as it had a hole burnt in it ! Observational repair is so useful, no matter how complex a system is, a very very good look can lead to a fix without in depth knowledge of a circuit.

The motor still would not spin ! I swapped the motor wiring over, it drove the other motor just fine so I stripped the non functioning motor.

It was tiny (fortunately not as tiny as the rear rotor !). Inspection showed that one of the tiny leafs of metal that act as brushes to the commutator had vapourised, probably an over current situation took out the brush and mosfet.

I thought this was dead and buried but I managed to re form the contact by bending it differently, the motor now worked and the helecopter was airbourne once again !