1997+ Mercury 35/40HP 2 Cylinder Outboards Service Manual PN 90-826148R2, Page 62Get this manual
Principle Of Operation, CDM without Timing Protection Module (TPM) The ignition system is alternator-driven with distributor-less capacitor dischargeMajor components of the ignition system are the flywheel, stator, trigger, capacitor discharge modules (CDM and spark plugsThe stator assembly is mounted stationary below the flywheel and has capacitor charging coils wound in seriesThe flywheel is fitted with permanent magnets inside the outer rimAs the flywheel rotates the permanent magnets pass the capacitor charging coils causing the coils to produce AC voltage (260 320 volts)The AC voltage then is conducted to the capacitor discharge module (CDM) where it is rectified and stored in capacitorThe trigger assembly (also mounted under the flywheel) has coilThe flywheel has another permanent magnet located around the center hubAs the flywheel rotates, the magnet passes the trigger coilThis causes the trigger coil to produce AC voltage pulse which is sent to an electronic switch (SCR) within the CDMThe SCR switch discharges the stored voltage of the capacitor into the primary side of the CDM's ignition coilCapacitor voltage within the CDM is amplified as high as 45000 volts to jump the gap at the spark plugThe proceeding sequence occurs once-per-enginerevolution for each cylinderSpark timing is changed (advancedretarded) by rotating the trigger assembly which changes each trigger coil position in relation to the permanent magnets on the flywheel center hubA rev-limiter (over-speed protection) circuit is contained inside the trigger assemblyThe trigger pulse(s) provide power for the rev-limiter circuit, this circuit in turn counts the trigger pulses to determine engine RPMIF the engine RPM increases above the specified RPM limit, the rev limiter will prevent the trigger pulses from reaching the CDM eliminating spark delivery to the cylinderThe Rev limiter will start to limit at 5900 150 RPM and fully limit at 6200 150 RPM