CDI problems 1979 402 motor

Howdy,
We recently lost spark on our motor.
After testing the ignition system it was discovered that our cdi unit (part #332-4911) was u/s and needed replacing.
A new genuine unit was purchased and fitted and the motor ran fine for about a day and now we have no spark again.
After running some more tests it was discovered that the CDI unit was again U/S and needed replacement. These units are not cheap and my question is what can cause these units to fail? All other components on the engine have been tested by our local dealer and are ok. He recommends replacing the trigger assembly this time as a precaution but I feel we are being '' parts changers'' and not ''problem solvers".
Does anyone else have experience with this type of problem and what precautions can be taken to stop this happening again?

Thankyou in advance.

Re: CDI problems 1979 402 motor

Several things could cause this but the #1 item would be a faulty/miswired key switch or decayed harness that is allowing 12volt feedback on the kill circuit. Make sure the mercury switch is good and its wiring is ok as it can cause a no spark issue but not "blow" a pack. Also a bad coil can cause a inductive "kick" and damage pack and usually the ferrite core is broken or damaged....

Re: CDI problems 1979 402 motor

Is that the ferrite core in one of the coils?
Thanks.

Re: CDI problems 1979 402 motor

Yes..

Re: CDI problems 1979 402 motor

Can a cracked core in a coil be detected by voltage/electrical checks alone?
Or is there another way to detect if a core is broken?

thanks

Re: CDI problems 1979 402 motor

You can inspect visually or send to CDI and have tested as they have a tester for this. Cost about $15-20 a coil and no.. a meter/voltage/ohm test cannot check this.

Re: CDI problems 1979 402 motor

I have discovered that the rectifier is not working. Can this cause a CDI unit to fail?

Thankyou