Troubleshooting and Diagnostics Flashcards

A switching power supply produces excessive output ripple. The most likely failed component is:

Answer: The output filter capacitor

A degraded output filter capacitor loses its ability to smooth the switching waveform, resulting in high ripple.

When diagnosing a noisy audio amplifier, injecting a clean signal at the output stage and working backward is known as:

Answer: Signal injection troubleshooting

Signal injection involves applying a known test signal at various points to isolate the stage where the fault occurs.

A PNP transistor is suspected faulty. Using a DMM in diode-check mode, the base-emitter junction should read approximately:

Answer: 0.6–0.7V with positive lead on emitter, near OL reversed

For a PNP transistor, the base-emitter junction forward biases with the positive lead on the emitter (P-type).

An oscilloscope probe is set to 10X attenuation. If the screen shows 5V peak, the actual circuit voltage is:

Answer: 50V peak

A 10X probe attenuates the signal by 10, so multiply the displayed voltage by 10 to get the actual voltage.

A logic analyzer is preferred over an oscilloscope when troubleshooting:

Answer: Multiple simultaneous digital signal timing relationships

A logic analyzer captures many digital channels simultaneously, making it ideal for analyzing timing, protocols, and bus activity.

A ceramic capacitor measures near-zero resistance with an ohmmeter. This indicates:

Answer: The capacitor is shorted

A good capacitor briefly shows low resistance then rises as it charges; a permanently low reading indicates a short.

In a three-phase motor controller, one phase is missing. The likely symptom is:

Answer: Motor draws excessive current, runs hot, and may not start under load

A missing phase forces the remaining two phases to carry full load current, causing overheating and torque reduction.