Chainsaw Repair

Learned something new from a ole timer in the small engine repair for around 46 years. Think he said he was in his 70's.   

Called me and wanted to know if I had a coil for a S25da. I just so happened to have one pulled I parted out.

He went on to tell me he has only seen this happen once in all his time and now it makes 2 times.

Saw will not shut off.  Switch good, wires ground etc all good. Something goes wrong in coil and wont allow it to shut off.
I had never heard of such.

I sent him a coil and he installed it and it now shuts off.  Coil was the problem.

Anyone else ever heard or seen this before. Coils locked in run and never shuts  off when you try everything in the book.

Stihl 042 he said about 20-25 years ago.

Most of the coils I'm familiar with shut off by grounding through the switch so it does seem any break in
that small little wire would result in that symptom. When I think about it, I'm surprised it doesn't happen
more often, given the conditions I usually find under the recoil housings of saws I'm asked to repair. .   

I have no clue what happens.

The ole timer told me no type of grounding would shut these 2 coils off that I mentioned in OP.

Just shared so others would know if it happens to them to try another known good coil.