Author Topic: Echo 3900  (Read 3965 times)

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Offline Cut4fun .

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Re: Echo 3900
« Reply #20 on: September 11, 2012, 08:57:06 pm »
Coil part # 15660137330

Pretty neat read I just stumbled on.


The Echo CS-3900 Chain Saw ignition coil [module] has an armature and is U-shaped with two ends [sometimes three ends] facing the flywheel. The coil also has two sides. The primary side has thick wire wrapped around one leg approximately 150-200 times. The secondary side has very thin wire wrapped around the primary windings approximately 20,000 times. The flywheel has two imbedded magnets, a north and a south pole. When the magnets pass the U-shaped iron cores on the ignition coil, the primary winding builds voltage up to approximately 200 volts. Then, the electronic control module trigger breaks the current and sends it to the secondary side of the coil building voltage up to 20,000 volts used to fire the spark plug.

The Echo CS-3900 Chain Saw ignition chip is a trigger device that determines when the coil needs to fire the spark plug. It works by breaking the current from the primary side and sending it to the secondary side of the coil. This transfer steps up the voltage to fire the spark plug. The ignition trigger replaces points and the condenser on most chain saws having just two magnets [north and south]. If a flywheel has more than two magnets, then the ignition chip trigger will not work.

Note: On Stihl models 031, 032 and 041 these coils have a spark advance built into them and the ignition chip will cause misfiring.

To test the Echo CS-3900 Chain Saw ignition coil, disconnect the ignition switch wire at the ignition coil. Using a good quality spark tester, pull the starter rope with a good fast pull and check for spark. Removing the spark plug makes this process easier since it reduces the resistance when pulling the starter rope. If no spark is visible, remove the Echo CS-3900 Chain Saw ignition coil and sand the bottom of the coil. Also sand the mounting surface where the coils are attached to ensure a good and proper grounding of the ignition coil. Note: On some saws, the ignition coil bolts onto a plastic housing with a ground wire running to the cylinder or crankcase for a ground.

The high voltage from the ignition coil travels through an insulated spark plug wire to the terminal on top of the spark plug, then travels down the electrode threw the porcelain insulator to the ground electrode which is connected to the metal bottom body of the spark plug and is screwed into the cylinder.

Spark plugs can either have a metal gasket to seal the spark plug to the cylinder or a taper spark plug to seal the spark plug to the cylinder. The heat from the Echo CS-3900 Chain Saw spark plug is dissipated to the cylinder to help keep the spark plug cool.
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