Hello Peter,
A common failure mode with any type of ignition system (coil, magneto or CDI) is EHT overvoltage, which quickly leads to internal insulation breakdown in the secondary coil. Once the coil's internal insulation is damaged...your ignition system is finished...dead.
A common cause of this catastrophic insulation breakdown will occur if the sparkplug lead is intentionally or
unintentionally disconnected from the sparkplug while the engine is running or being hand cranked. The extremely high voltage (EHT) excursion from the coil is limited by the ionisation of the spark plug gap (typically around 12 KV in a model spark plug). If the spark plug gap is absent for whatever reason, the coils output voltage will continue to rise even higher, until eventually it finds a weakness in the coils internal insulation. Once the coils internal insulation fails, it's game over.
Excessive oiling of a spark plug can also prevent the spark occurring, which again will put the coils internal insulation under added stress. Most full size aircraft engine magnetos have a safety spark gap built into their design to protect the coils internal insulation from the damaging overvoltage. The safety gap is set a little wider than the spark plug gap. The idea is, if the spark plug fails to spark, for whatever reason, the the safety gap will arc over at a slightly higher voltage, thus protecting the coils internal insulation.
There could be other possible causes of failure of your ignition module; manufacturing quality is a big unknown.
Cheers
Mike
