Stihl 041 AV Electronic - No spark

[JonCraig]

The "big thing the coil bolts to" is apparently called the "Stator". You're saying that would need to be replaced, rather than the coil/module (the smaller, black, solid-state unit)?

[bgsengine]

Correct - If it was a solid state ignition module (You got to remember they did not have the tiny I/C circuits back then in the early 70's that make today's little ignition modules possible) it would not be referring to it as "Ignition Coil" - The stator plate is what replaces the points - I have had a few of these apart over the years.. and replaced a couple of those stator plates for no spark.. (E-X-P-E-N-S-I-V-E even back then) - unless I miss my guess that is the actual CDI/Electronic Module that manages the timing and voltage through the coil - as I said I would start first by doing some basic resitance checks on the coil itself before even thinking about the solid state module being bad.

Yours is an "early production" SEM coil and module - the coil is separate from the ignition module components (stator plate) but as it is solid state it is rare to need that plate - which is why I suspect you have a continuity problem in the coil or wiring - can't see how just cleaning it would have damaged the electronic module.

[JonCraig]

What sort of impedences would I be looking for? Testing the coil off the saw (ie, no other connections to interfere with the reading):

Plug wire connection to ground on the coil = 2.071 KOhm. I'm assuming this is the secondary.

The other, little wire that connects to the stator to ground = 0.1 Ohm. ie, basically a dead short. If this is the primary (and there's no solid state circuitry in this box), then that seems like a shorted coil to me.

Thoughts, and thanks as always. You guys never cease to educate me!

--JC

[bgsengine]

thats where an accurate meter comes in handy - and knowing how to read it -

The primary (small wire) would be expected to be in the range of a few hundred ohms (200-600 ohms) while the secondary may be in the range of 2-6K ohms if you genuinely show a tenth of an ohm reading on the primary wire to coil ground, I would think that is almost surely the issue - like you said a dead short.

Perhaps a Stihl guy can come along with exact specs on the coil and diagnosis of the ignition - but from your stated history of cleaning the unit up, I would be taking a close look at the point where the small wire goes in to the coil and see if there's not maybe broken insulation there somewhere.

[KE4AVB]

Per the service manual the SEM coil should be 0.4-0.5 ohms Primary; 2,700 - 3,300 (2.7K - 3.3K) ohms Secondary.

[JonCraig]

My meter is a Fluke 115, and I was an electronics minor in college. Double checked the kill wire and all looks good there. Just ordered a NOS coil off ebay.

Will update when it comes in--hopefully without asking for a source for a stator!

[wristpin]

If the coil is good would it be possible to use an after market trigger module such as a Nova or a Meco?

[JonCraig]

From my reading elsewhere, using a Nova is only possible if using the points-type flywheel, not this ignition. Presumably something to do with the magnets. So if, on this one, it is the stator, that's probably the direction I'll be looking.

[bgsengine]

From my reading elsewhere, using a Nova is only possible if using the points-type flywheel, not this ignition. Presumably something to do with the magnets. So if, on this one, it is the stator, that's probably the direction I'll be looking.

I believe you are correct -

I *THINK* (Not even remotely sure) the stator contains the primary charging coil - much like other SEM ignitions I have worked with on Jonsered and Husqvarna where they had the charge coil by the flywheel and the secondary (spark) coil mounted separately (In the air box) - you need both coils to produce spark.

[JonCraig]

Got a NOS coil a few days ago and finally had a chance to play with this thing again today. Still no spart with the new coil. So now I'm faced with either trying to source a new Stator, or convert the whole deal to points. Questions:

Anyone have a good source for a new stator?

Alternatively, I've never replaced a points ignition with one of those Nova modules before. How complicated would it be to convert this saw to one of those setups? There are a couple points-type flywheels on ebay and are cheap enough. What is involved in the conversion? Maybe a better question is: can anyone point me towards what module to use and an instruction manual? Atom seems to be another brand of the same sort of deal. I just can't figure out (without seeing, I'm hoping) how on earth you can time the saw with a module mounted externally…?