Electrical Systems Diagnostics Flashcards

A technician is diagnosing a parasitic draw on a piece of equipment. With the ignition off and all accessories turned off, the multimeter, connected in series with the negative battery cable, reads 250 mA. What is the most appropriate next step?

Answer: Begin pulling fuses one by one while observing the multimeter reading.

A parasitic draw of 250 mA (0.25 A) is excessive; a normal range is typically under 50 mA. The standard procedure to isolate the source of the draw is to pull fuses one at a time. When the fuse for the problematic circuit is pulled, the amperage reading on the multimeter will drop significantly, identifying which circuit contains the fault.

When testing the AC voltage output from a stator on a small engine, where should the multimeter leads be placed?

Answer: Across the two stator output wires (or pins) coming from under the flywheel housing.

The stator produces alternating current (AC) voltage. To measure its total output, the multimeter, set to AC volts, must be connected across the two output leads from the stator itself, before the voltage regulator/rectifier. This tests the stator's ability to generate voltage independently of the rest of the charging system.

A technician performs a voltage drop test on the starter motor's positive cable. With the engine cranking, the multimeter reads 0.8 volts. What does this reading indicate?

Answer: There is high resistance in the positive side of the starter circuit.

A voltage drop test measures the amount of voltage 'lost' due to resistance in a circuit. A reading of 0.8 volts on the positive cable during cranking is excessive; a general rule of thumb is that it should not exceed 0.5 volts. This indicates a problem such as a corroded connection, a damaged cable, or a faulty solenoid contact on the positive side of the circuit.

While testing an electronic ignition coil with a multimeter set to ohms, a technician measures the resistance of the secondary winding. What would a reading of 'OL' or infinity most likely indicate?

Answer: There is an open circuit or break within the secondary winding.

The secondary winding is a very long, fine wire. A reading of 'OL' (Over Limit) or infinity indicates infinite resistance, meaning there is a break in the winding and the circuit is open. A short circuit would show as a very low resistance reading, not an open one.

Which of the following components in a small engine's charging system is specifically designed to act as a voltage regulator by allowing current to flow in reverse once a specific voltage is reached?

Answer: Zener Diode

A Zener diode is a special type of diode designed to operate in the reverse-biased condition. When the voltage across it reaches the 'Zener voltage,' it conducts in reverse, effectively shunting excess voltage to ground. This characteristic allows it to be used as a simple and effective voltage regulator in small engine charging circuits.

A customer's zero-turn mower clicks once when the key is turned to the start position, but the engine does not crank. The battery is fully charged and the connections are clean and tight. Which of the following is the MOST likely cause?

Answer: A faulty starter solenoid.

The single click indicates that the starter solenoid is being energized (receiving power from the key switch) but is failing to make the high-current connection to power the starter motor itself. This can be due to burnt internal contacts or a mechanical failure within the solenoid. A seized engine would typically result in a loud 'thud' and no crank, while ignition and fuel issues would allow the engine to crank but not start.