Abstract: A simplified, electronic circuitry, testing apparatus for performing voltage, continuity, open circuit or dynamic signal substitution testing of each individual major component within an automotive-type transistor ignition system preferably having a multi-function control for connecting a single pair of test probes to any of various test circuitry subcircuits thereof, a signal generator may be included therein, a plurality of discrete display components integral to the test subcircuits may display test results, this testing apparatus being capable of being powered by the electrical power source for the engine ignition system and preferably containing safety devices for preventing electrical damage to the ignition system under test or to the testing apparatus itself; preferably a separate adapter component and a separate spark indicator component which establishes a precise test spark gap may be connected as part of the testing apparatus.

Abstract: Faulty alternator diodes are identified by detection of a voltage ripple across the terminals of the automotive storage battery. A diode is forward biased whenever the battery has adequate charge to be designated a "good battery", and the forward bias condition is utilized as a reference potential. A voltage divider scales the reference potential, and couples it to the inverting terminal of a comparator. The non-inverting terminal is biased at a predetermined differential from the inverting terminal, and the probe signal is AC coupled to the non-inverting terminal. If a diode is bad, the superposition of the AC with the bias will switch the comparator and energize a light emitting diode.