IGNITER FUNCTION Re: john deere 170 riding mower W/kawasaki 420v motor (NO START)
This information relates to the LX172, it replaced the 170 and actually uses the same igniter (also called ignition module). The igniter serves several functions, it grounds out the coil to shut the engine down when the ignition switch is turned off, or when a safety switch is activated . It will also prevent the engine from starting via the seat switch, neutral switch, or PTO switch. The 170 has different switches, but they do the same thing. The main function of the igniter is to trigger the coil causing a discharge of high voltage current from the coil windings to the spark plug. It has to be connected from the igniter to the coil to work. The LX172 has two wires connected to the igniter at the single spade connector, you can disconnect the second wire that connects the safety switches and ignition switch to test for a spark but if you try to start the engine with the wire disconnect the safety switches, fuel shutoff and ignition switch will not shut off engine. Below is the JD explanation.
With the neutral start/brake switch closed, current flows to the ignition relay energizing the coil, closing the relay. Closing the relay breaks the path to ground for the ignition coil current and sends current to the fuel shutoff solenoid (Y1). An alternate current path is provided to keep ignition relay energized when the PTO is engaged, the transmission is engaged, or the brake pedal is not depressed. With the operator on the seat, the seat switch (S2) is closed and current flows to the ignition relay coil keeping the relay energized.
As the flywheel turns, a magnet in the flywheel starts to align with the ignition coil and produces current in the primary coil by electromagnetic induction. In the initial stage low voltage current is produced. The low voltage current flows to a transistor (C), and resistors (A and B) in the ignition module (A1). Resistor (A) has high resistance so current will flow through resistor (B) to transistor (C). The transistor base is energized which closes the transistor and provides a path to ground for ignition coil current flow.
In the spark stage (spark produced), the flywheel magnet is fully aligned with the ignition coil and high voltage (maximum) current is induced in the primary coil. The high voltage current can now flow through resistor (A) to transistor (D). The transistor base is energized which closes the transistor and provides a path to ground for current that was flowing to transistor base. With current no longer applied to transistor base, the transistor opens breaking the path to ground. The sudden reduction of current flow, induces high voltage current in the secondary coil. The high voltage current flows through the coil wire to the spark plug (E1). The voltage is now high enough to jump the spark plug gap and a spark is produced, igniting the fuel/air mixture in the cylinder.
