SUCCESS!!! Just repaired Stihl 045/056 Bosch electronic ignition!!!!!

[foggysail]

Dustin- if you got a shock "touching" the ignition, it is functioning. I don't know of an easy way to get at the center pin on the pulse transformer the black thing into which the high voltage plug wire is inserted. And yes, there could be something else at fault with your ignition.

It is important to remember that when you are looking for an arc in the plug, THE BODY OF THE PLUG MUST BE GROUNDED. A clip wire to ground from the plug body (not the center pin of teh plug) works.

Couple of suggestions if you are testing with the plug body properly grounded. First, examine the transformer especially around where the plug wire enters it. What you are looking for are carbon track marks that provide a current path (along with arcing maybe) for the high voltage ignition pulse.

Whether you see anything or not, put a light spray of WD40 on the transformer especially around where the plug wire enters it. The oil will provide insulation for any arc path.

Is there anyway that you can push an insulated wire into where the plug wire when seated resides? If so, try removing the insulation from the tip of the new wire and plug it into the transformer. Consider using hot glue to temporally hold it in place. The wire should be about a foot in length. So if you get this far, take the other end of the wire and point it towards a grounded surface on your saw.....cylinder head for example and pull the starting cord. This is a test of teh spark plug wire itself. If you DO have a spark jumping from the new wire, then of course the plug wire has failed.

Let us know how you make out

Foggy

 

[shu7241]

Have read these posts from day one to present, very interesting. For foggysail. Do you have a schematic of the stihl ignition system? If so could you put it online for the rest of us to see. I have friends who tinker with small engines and they have never heard of this fix. Thanks. Bill

 

[kwhite87]

Hey foggysail, I am having issues with an 051 Bosch unit. Looks similar but isn't the same. Have you fiddled with any of those before or suggest maybe I dig into it?

Edit: it may not even be Bosch.

 

[foggysail]

Hey foggysail, I am having issues with an 051 Bosch unit. Looks similar but isn't the same. Have you fiddled with any of those before or suggest maybe I dig into it?

Edit: it may not even be Bosch.
View attachment 468029

No idea what that ignition is; sorry!

 

[foggysail]

Have read these posts from day one to present, very interesting. For foggysail. Do you have a schematic of the stihl ignition system? If so could you put it online for the rest of us to see. I have friends who tinker with small engines and they have never heard of this fix. Thanks. Bill

Bill-- I do have the schematic in a file someplace. I'll look for it and post it. It is not very complicated. Just remember, I ripped apart an ignition to learn how it was electrically constructed. I was not concerned about component values after I located teh failure mechanism which is the "capacitor" that all are now familiar with.

 

[shu7241]

Thanks for your reply. I am sure your fix works, I am just curious about grounding one side of the capacitor. Isn't that what the second lead does. I have looked on Google imagines at other electronic ignitions and haven't seen any where the charging capacitor is grounded on one side. I am not being argumentative, just trying to understand. Thanks. Bill

 

[hotshot]

Thanks for your reply. I am sure your fix works, I am just curious about grounding one side of the capacitor. Isn't that what the second lead does. I have looked on Google imagines at other electronic ignitions and haven't seen any where the charging capacitor is grounded on one side. I am not being argumentative, just trying to understand. Thanks. Bill

See the attachment in post #96 on page 5, it is very close if not the exact CDI

 

[foggysail]

Hotshot-- I just tried to pull the attachment, somehow it didn't come up. I do though remember looking at it after your post so its most likely pretty much the same as what I found in my analysis. In any case, I will try to find the schematic in my files and post it.


Bill-- You don't have all the circuitry. First, a capacitor charges to some voltage ( V) as long as there is a current ( i) flowing into it whereby

V = (i)x(t)/c where t is in seconds and i in amperes which itself is qxt where q is coulombs and t in seconds; c is in farads and V is in volts. For a constant current flowing into the capacitor, there is a linear voltage rise. Note that the smaller value of c, the greater change in voltage for a given i and t but see the formula for energy below. Once the capacitor is charged.......think of it as a bucket fulled with coulombs.... it will remain charged until it is discharged.

The reason fro having one side of the capacitor....IN THIS CIRCUIT ONLY or similar circuits.........is that ground....which conducts.... is a path for the capacitor to discharge through.

The ignition circuit charges the capacitor through magnetic coupling and a diode that allows current to only flow in one direction, into the capacitor. But a charged capacitor is of no value unless the charge can be used. So to make use of the charged cap (energy = cxv^2 or the capacitor value times the voltage charged squared) the charged cap is discharged with an electronic switch called an SCR, silicon controlled rectifier through the high voltage pulse transformer whose output is a ratio of the primary winding and the secondary winding to produce the high voltage pulse that causes an arc in the spark plug.

Save above until I can find teh circuit schematic and then it should make sense.

Foggy

 

[shu7241]

Hotshot-- I just tried to pull the attachment, somehow it didn't come up. I do though remember looking at it after your post so its most likely pretty much the same as what I found in my analysis. In any case, I will try to find the schematic in my files and post it.


Bill-- You don't have all the circuitry. First, a capacitor charges to some voltage ( V) as long as there is a current ( i) flowing into it whereby

V = (i)x(t)/c where t is in seconds and i in amperes which itself is qxt where q is coulombs and t in seconds; c is in farads and V is in volts. For a constant current flowing into the capacitor, there is a linear voltage rise. Note that the smaller value of c, the greater change in voltage for a given i and t but see the formula for energy below. Once the capacitor is charged.......think of it as a bucket fulled with coulombs.... it will remain charged until it is discharged.

The reason fro having one side of the capacitor....IN THIS CIRCUIT ONLY or similar circuits.........is that ground....which conducts.... is a path for the capacitor to discharge through.

The ignition circuit charges the capacitor through magnetic coupling and a diode that allows current to only flow in one direction, into the capacitor. But a charged capacitor is of no value unless the charge can be used. So to make use of the charged cap (energy = cxv^2 or the capacitor value times the voltage charged squared) the charged cap is discharged with an electronic switch called an SCR, silicon controlled rectifier through the high voltage pulse transformer whose output is a ratio of the primary winding and the secondary winding to produce the high voltage pulse that causes an arc in the spark plug.

Save above until I can find teh circuit schematic and then it should make sense.

Foggy

 

[shu7241]

Foggy, that makes it very clear, I completely understand it now. Ha-Ha. I did not see schematic in earlier post. There is no need to dig out your drawing. A friend of mine dug out the epoxy in his ignition, I opened the circuit and ordered capacitors. If and when we get everything back together I will post the results. Thanks again. Bill

 

[foggysail]

Bill--

The only thing I ask is to keep the forum informed of your progress so ALL can benefit. Today we are still waiting for Dostin's status with his problem. His last post, 402 leaves the board hanging after my suggestions. To my knowledge his is the only mod that supposedly failed even though he indicates that a high voltage was present when he received a shock. But if his saw has no spark...........

Good luck and enjoy

 

[54stude]

Bill--

The only thing I ask is to keep the forum informed of your progress so ALL can benefit. Today we are still waiting for Dostin's status with his problem. His last post, 402 leaves the board hanging after my suggestions. To my knowledge his is the only mod that supposedly failed even though he indicates that a high voltage was present when he received a shock. But if his saw has no spark...........

Good luck and enjoy

Based on your description, is it possible that dustin's saw has the capacitor not grounded, or the polarity wrong?

 

[foggysail]

The capacitor is not polarized---. I believe he has the capacitor installed correctly because he reported that he received a shock when pulling the starter cord.

 

[texican65]

Well how'd it go, did anybody send you one? I've got an early '80s 056 mag II that had a bad electronic SEM ignition, I ripped it out and replaced it with one of the Selettra ignition modules and she's a runner again. I've got that old SEM...is it the same as the Bosch...I don't think so? Will it help?

Dow

 

[JonCraig]

On my 041AV, the Bosch and SEM ignitions were drastically different. Flywheel was different too.

I'd assume they're different on the 056 as well.

 

[shu7241]

Foggy, that makes it very clear, I completely understand it now. Ha-Ha. I did not see schematic in earlier post. There is no need to dig out your drawing. A friend of mine dug out the epoxy in his ignition, I opened the circuit and ordered capacitors. If and when we get everything back together I will post the results. Thanks again. Bill

 

[shu7241]

Foggy, I hate to say it but my repair job was a bust but not because of the fix. Got everything put together, spun the flywheel and got no fire. Major disappointment. Checked everything out and found the secondary coil open. Earlier it had read 2300 ohms. Have no idea why coil opened up. Now looking for coil that don't cost $50. Interesting forum, thanks for the information. Bill

 

[foggysail]

Foggy, I hate to say it but my repair job was a bust but not because of the fix. Got everything put together, spun the flywheel and got no fire. Major disappointment. Checked everything out and found the secondary coil open. Earlier it had read 2300 ohms. Have no idea why coil opened up. Now looking for coil that don't cost $50. Interesting forum, thanks for the information. Bill

By "secondary coil" I presume you're referring to the coil used to charge the capacitor, not the coil (pulse transformer) that the spark plug wire mounts into. Strange that it should open because there are no really high voltages generated in that coil. But poop does happen! Not sure if I have one around here, if so I'll get back to you. I don't have many parts to this saw. Maybe someone who reads this thread will respond with help.

Foggy

 

[shu7241]

Foggy, No, just the opposite. To me, the primary is the low voltage coil , the secondary coil is the high voltage coil. Bill

 

[foggysail]

Foggy, No, just the opposite. To me, the primary is the low voltage coil , the secondary coil is the high voltage coil. Bill

Bill-- the "coil" with the plug wire attachment is a transformer designed for pulse applications; it has a primary and secondary winding. I refer to the transformer as a pulse transformer because its volt time integral core can support a pulse without entering into saturation. The second magnetic device is a coil that gets energy from the rotating magnet which is used to charge the capacitor that get discharged with the scr into the pulse transformer.