Mercury Force 9.9, 15HP Outboards Service Manual, Page 90Get this manual
AASEM-WALBRO IGNITION SYSTEM 1Theory of Operation SEM-WALBAO ignition is Capacitive Discharge Ignition with all of the standard components encased inside two modulesInside the modules there are four wi re coils of various size and length The module also contains several electron ic components, which are used to control the voltage flow and strengthThe SEM flywheel contains magnets placed inside the outer rimAs the flywheel rotates, the magnetic field will cut through the ignit ion module coreTh is core in turn creates stronger magnetic field inside the ignition module coi lsFlywheel rotation wilt cause the charge coil to generate negative, positive and then second negative pulseA diode will eliminate the two nega Ove pulses and supply the positive pulse to the capacitor for storageOnce the voltage is stored inside the capacitor, it is necessary to release this voltage through the primary wind ingsA small trigger coil will generate small voltage to ThyristorTrigger coil voltage is similar in form as the charge coilThe second negative pulse, the one right after the positive charging pulse, is used to turn the Thyristor on The Thyristor, in turnreleases the stored capacitor voltage to ground through the pri mary coil The sudden flow ofvoJtage through the primary coilinduces voltage rise inside the secondary coilSecondary voltage can reach approximately 30,000 volts, if needed, before bridg ing the spark plug gap and re turning to ground