Stihl 041 Super AVE - No Spark - SEM Electronic Ignition

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Yes, I don't know exactly where to cut and solder on your older Bosch circuit board, since the capacitor is located on the opposite side of the plate as compared to the newer ones that Foggysail modified.

It is noteworthy that in the later design implementation, Bosch moved the capacitor to the other side of the "can" where there is more volume.

Let's see if we can reason this out:

You mentioned being able to solder one side of the new capacitor to any ground available: Looking at Foggysail's solution, he chose to ground one side the new capacitor using a wire with a lug crimped to it, and attached that lug under one of the high voltage spark coil, hold-down screws. This would certainly provide a path to ground for one side of the capacitor.

The odd thing is, the Bosch circuit diagram does not show either side of the factory capacitor being directly grounded: One side goes to the anode side of the Thyristor and the other is attached to a ground path that goes through the low voltage windings of the ignition coil and to one side of the high voltage coil windings. At least that's what I read from the circuit diagram from the shop manual.

What I don't understand about Foggysail's solution, is why he grounded one side of the capacitor and why that allows the circuit to function properly to fire the spark. I would have thought the "fix" would entail circumventing the existing capacitor by disconnecting both capacitor leads and then connecting the new capacitor with wires which soldered to the appropriate circuit board connections, (after having cut the leads that went to the bad capacitor), effectively removing both sides of the bad capacitor from the circuit and providing the new capacitor the correct circuit connections to the Thyristor and to both sides to spark coil per the circuit diagram.

My understanding of electrical circuits is very limited compared to Foggysail's. Too bad we can't ask him what to do, but he hasn't been online since 2021. (or at least responded to a thread on the forum)

I think you perhaps you have mis-understood and mis-labled which is the primary and secondary spark coil connections in your labeled picture. I think you have reversed them; I have uploaded a picture which shows what I believe them to be. The Stihl shop manual circuit diagram shows the low voltage wire coming from the capacitor to the low voltage side of the coil to be the left wire on the right side of the spark coil and the right-most wire is connected to one side of the high voltage coil windings.

I have uploaded an edited picture which shows the wires labeled as I think they should be.

If I were you, I'd try to cut the lead on the circuit board that goes between the upper capacitor connection and the Anode of the Thyrister. (and the cathode of diode number 2) Doing so would isolate the bad capacitor from the circuit. Then if you can solder a new wire upstream of the cut lead (attaching it to the Thyristor and diode 2, and run that wire to one side of the new capacitor, it should be a simple matter to solder a second wire to the point on the circuit board which goes to the primary side of the spark coil (and secondary side).

I've uploaded a diagram showing the suggested locations. Severing the one side of the capacitor circuit should isolate it and enable the circuit to be completed by the new soldered wires and new capacitor located out from under the hot flywheel environment.

Examining the photograph you made of your stator with the epoxy removed, is very difficult for me to make out each of the electrical components and their soldered connections that you've exposed. So I can't tell you where exactly to cut, except to do so, by the upper factory capacitor attachment point to the circuit board. I can't tell where the Thyristor is located. If you could locate the anode side of the Thryistor, and solder one wire to it, after cutting the lead to the bad capacitor, you'd be halfway there. Then just solder the second wire to the wire that goes to the primary side of the spark coil. That should work.

Again, I don't know why Foggysail's solution involved grounding one side of the new capacitor, but my proposed solution, should work as well.

Hope this helps. Good Luck!
 

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Yeah, about Foggy's solution, it's also unclear to me about the other wire being grounded, regarding the schema, same as you.

My reasoning on HV and LV wires is twofold:
1) The kill-switch wire goes from LV coil and it's coming out from the stator plate on the left side, so corresponds with the left wire coming out from the LV coil.
2) Since HV coil should have much more windings than LV coil, I'm guessing that the LV coil is that orange thing on the top. because it's much smaller than the black one beneath.
3) The right wire on the right side is coming out of that LV coil, while the left one is coming out of HV coil.

But, as you said, we can disregard all that crap and just go with a no-nonsense approach: We see 2 capacitor contacts and adjacent copper leads.
Cut near the contacts and solder two wires from a new capacitor near the cut and that's it.
Maybe. :D
 

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The "orange thing" is certainly part of the spark coil. Whether it is the high voltager or low voltage side is tough to figure out. All the coils I'm familar with usually have the primary side wrapped around an iron pole of sorts, and then the secondary, high tension windings are wrapped on top of the primary windings. I suppose it doesn't matter which is wrapped a round the iron pole.

What is interesting or remarkable to me about how such coils actually work is this: In the old days of points ignition in automotive applications (and chain saws as well), when the points were closed the 12 volt current flowed through the primary side of the coil, creating magnetic flux lines. When the points open, the magnetic field collapses, causing the high voltage current in the secondary windings to occur, thus firing the spark plug. Witih the advent of CDI ignitions, it is my understanding that the high voltage current is generated when the charge from the capacitor is released, which causes an extremely rapid magnetic effect to course through the primary windings and the secondary windings.

The point being the spark plug fires on the increase waveform of the magnetic field, not the collapse of the magnetic field when the points open.

Anyway, I hope your cut and solder locations work out satisfactorily. And the saw roars to life again!
 
It doesn't matter whether current gets stronger or weaker in the LV coil, important thing is that it changes, that's what induces current in the HV coil.
Anyway, thanks for all you help, time and patience.
I'll probably take this to a friend with much more theoretical and practical electronic knowledge and figure it out.
 
I've have owned a Stihl 041 super AVE for 35 years and it finally died from a "no-spark" condition. This one has the SEM version of the electronic ignition. Researching the forums and looking on fleabay, I am unable to locate a replacement SEM coil. I believe the coil is an SEM Type GA coi which is used on Husky 2100's and some Dolmarsl, but I haven't pulled the flywheel yet. Any suggestions for replacement coils or other other solutions to make a spark at the right time? The saw ran really strong, excellent compression; the piston and cylinder show no scoring, so I'd prefer to fix it than junk it or sell it for parts. Thanks in advance for responses.
There is an ignition chip called: "Nova 2". Some Stihls may work that were once points with this aftermarket generic chip. They cost about $20.
 
There is an ignition chip called: "Nova 2". Some Stihls may work that were once points with this aftermarket generic chip. They cost about $20.
Mate I had experience with my 031, replaced coil with Chinese knock off and ignition timing then SEVERELY ******** using an electronic chip Atom brand.( Australian item now not available) I made a post on that you can find under Hard Starting I think it was. Ended up discarding Woodruff key and retiming using flashing power timing light.
 
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