Re: 1977 9.9 Johnson ignition troubleshooting procedure

[Don]

Feel a bit out of my element, your electronics knowledge far surpasses mine for sure, but will try!
OK, your "driver coil" terminology equates OMC’s "charge coil". I find OMC’s terminology very confusing as well, because the term charge coil makes one think of an alternator or battery charging circuit, which is not the case. The charge coil is just what you described: "the coil that generates the AC voltage that gets stored in the capacitor…….". The charge coil is just a simple winding of wire that generates voltage when the flywheel magnets pass by it. The charge coil voltage/current is rectified to DC and stored in the capacitor inside the "power pack". The charge coil leads are found in the four pin connector coming out from under the flywheel, the leads are brown and brown/yellow tracer. I don’t have the exact resistance spec, but am thinking it is around 400 ohms, and there should be no shorts to ground or the mag plate.
The component I was referring to, the sensor coil is another simple winding found under the flywheel, its leads are found in the four pin connector and are black and white/black tracer. This component is what sends the low voltage to the powerpack which operates the SCRs allowing the capacitor to send its stored voltage to either one of the to coil primary circuits. One sensor coil operates both coils because the powerpack can sense sensor voltage polarity. The sensor resistance is usually about 15 ohms, and there should be no shorts to ground/mag plate.
Again, these components are just simple windings and rarely fail. They do get damaged physically when hit by flywheel magnets or debris under the flywheel. The other obvious damage to look for is damage to the harness/leads coming out from under the flywheel, wires can get melted from overheating or if they have been rubbing on the flywheel. Taped up bulges in the harness are usually good indications of previous harness/wiring repairs.
All the fancy electronic circuitry is inside the powerpack, there are no resistance tests that can be performed on the powerpack with the exception of testing its ground lead. Resistance between the powerpack ground lead and a good engine block ground should be less than one ohm.
The engine is shut off by killing spark, the powerpack’s capacitor is drained to ground when you press the stop button. The best way to test for stop button problems is to eliminate it from the circuit, and the best way to do this is to push the black stop button pin out of the three wire rubber connector next to the coils, then reconnect the plug connector and try for spark again. Please do not simply cut the leads, then make repairs with butt connectors. I’m sure you can figure out some way of pushing that pin out of the connector. Soak the rubber boot in alcohol first, this usually helps loosen things up a bit. Please do not use WD 40 or any sort of lubricant spray, this may cause shorts later on.
Finally, it is pretty simple to just substitute another known good powerpack. No need to remove the old powerpack, just substitute the connections and ground the substitute pack’s ground lead using one of the thermostat cover screws.
Hope this is helpful to you…Don
PS-The powerpack substitution test is not a substitute for doing basic tests, but can at least tell you something….All components should be tested before just replacing the powerpack to ensure a marginal component does not damage the powerpack in the future…