1978 Evinrude Outboards 9.9/15HP Service Manual, Page 32Get this manual
After the capacitor is charged, the flywheel continues to rotate so the magnetic field of magnet passes through the sensor coil winding, producing alternating currentCurrent leaves the sensor coil through wire (a) which is positive (+), and enters the power packCurrent flows through diode to the #1 S.C.Rgate, turning on S.C.R#1 and returns to the other side of the sensor coil through diode DCurrent flow is blocked by diodes and CWhen the opposite flywheel magnet is passed by the sensor coil, current flow is reversed, and wire (b) is positive (+)Current enters the power pack and flows through diode to the gate of S.C.R#2 turning on S.C.R#2 and returns to the other side of the sensor coil through diode ACurrent flow is blocked by diodes and bypasses diode D
1Flywheel magnet 2Charge coil 3Wire (a) 4Inside power pack 5Diode 6Engine ground
7Capacitor 8Diode 9Diode C
10Diode 11Wire (b)
Figure 4-2Capacitor Charge Circuit
The four diodes in the triggering circuit direct current flow to the S.C.Rgates and back to the sensor