disassemble a cdi, magneto, coil

There's 2 amatures that prtrude from the plastic casing that pick-up the magnets on the flywheel and make electricity. There is also a wire that acts as a safety switch to ground the spark in the event the handle is released.

Right now, I'm not getting a meter reading from either side of the U (contacts) to the plug wire, I think I should be???

Oddly, both sides of this U (pick-ups) are giving me a reading to the kill switch wire. I've got it out of the mower! Both of the pick-up (sides of the U) are grounded to the motor block. There must be a snubber inside the unit itself to prevent the current from reversing and going to ground on the block.
 
Yep, as Gearnut says, often there'll be a step-up transformer with two separate isolated windings, or, alternately, it will be an auto-transformer with a common ground.

External bench-testing will be useless unless you know precisely what's inside.

Also, most common potting mixes are thermo-setting 2-part plastics and will not melt with heat. They will soften slightly at about 60 degrees Celsius, but that's about it, they won't do much else until they begin to burn. I've tried 'de-potting' circuits in the past, without much success.

I've attached a block diagram as drawn by another member some time ago. (Sorry, can't remember who for credit where it's due.) In this circuit, an auto-transformer is shown.


machiasmort, just saw your latest post. By 'armatures', do you mean wires?
Next question, what 'U' contacts?
Don't expect continuity between wires. There can be a lot going on that you can't see, as I mentioned earlier. Chances are there's a series capacitor or a semiconductor here and there that prevents continuity testing. There's no way you can determine what's inside by external measurements. Modern electronics is more complex than that. You really are wasting your time.
(Prove me wrong, I don't mind.)
 

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What I'm calling armatures are the pick-up arms that pick up the magnet spinning on the flywheel and excite the coils thereby producing spark at the plug.

My question? Shouldn't there be continuity between those arms and the plug wire?

I never realized that only one side of the coil on our HT's was grounded!

I appreciate all of the help and ideas, because I am clueless on this one! If I get it to work, will be attributed to act of God unless somebody really knows their stuff out there well enough to help a blind man thru this!

Will post some pics in the days to follow. Thanks again!
 
Now I'm with you. Those 'arms' are the coil core. There definitely won't be continuity between them and the plug wire. The core is at ground potential.
(See the diagram that I posted above.)
 
TT, I've thought about it!

Steve, I appreciate your help greatly. I think I'm starting to understand a little more.

Using the refferenced names on the schematic, Magnets pass the coil core, charging the exciter. Exciter then passes the charge to the diode (keeping it flowing one direction) and then to the capacitor where it is stored till there is enough juice. When the Cap hits it's limit it sends the juice to the "zero crossing switch" (point right?) which ok's it to go to the larger coil to be amplified and sent to the plug.

I've got a feeling this thread might help somebody else out latter?

So the reason I might not be getting continuity between coil core and plug wire is due to the fact there is a Capacitor in line with the flow of electricity.

With all of the garbage in landfills, you'd think our Government would make them(manufacturer's) produce these things to be recycleable. Like put the assembly in a water tight box which could be opened.

They stick their nose in everything else!
 
machiasmort said:
Using the refferenced names on the schematic, Magnets pass the coil core, charging the exciter. Exciter then passes the charge to the diode (keeping it flowing one direction) and then to the capacitor where it is stored till there is enough juice. When the Cap hits it's limit it sends the juice to the "zero crossing switch" (point right?) which ok's it to go to the larger coil to be amplified and sent to the plug.
Click to expand...

Yep, pretty much. I'm not sure just how accurate that schematic is, but it's the best I've seen so far. Probably not 100% accurate though.
In effect, as the magnet turns, it causes the two poles of the core to alternate between N-S to S-N, (hope you follow me), causing an alternating current to flow in the windings that are wound on the core.
The core itself has no electrical connection to the circuit, except to ground. It only conducts magnetic flux and not electricity as such.
As you say, then the alternating current is recified to pulsing DC by the rectifier diode, charging the capacitor. In the circuit would be a comparator, to sense when the cap is charged fully then trigger a transistor or MOSFET to dump the capacitor's charge into the primary of the transformer. The 'step-up' transformer ensures that several kV, (probably about 5kV-20kV), is applied to the spark plug.


So the reason I might not be getting continuity between coil core and plug wire is due to the fact there is a Capacitor in line with the flow of electricity.
Click to expand...

No. As mentioned above, the core is hard-wired to ground.


With all of the garbage in landfills, you'd think our Government would make them(manufacturer's) produce these things to be recycleable. Like put the assembly in a water tight box which could be opened.
Click to expand...

Potting prevents copying, though. Also, it helps conduct heat away without needing metal heatsinks.
All the same, I hate the unservicable nature of this stuff. In a way, give me points etc. any day.
 
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