Troubleshooting and Diagnostics Flashcards

A technician observes 60 Hz hum on an audio amplifier output with no input connected. The most probable cause is:

Answer: Power supply filtering capacitor failure or ground loop

60 Hz hum typically originates from inadequate power supply filtering or a ground loop coupling AC line frequency into the circuit.

When an IC chip becomes unusually hot during operation, the first diagnostic step should be:

Answer: Check for correct supply voltage and verify no output is shorted

Verifying supply voltage and checking for output shorts identifies whether the IC is being forced to dissipate excessive power.

A MOSFET gate-to-source resistance measures near-zero ohms. This indicates:

Answer: The gate oxide has broken down, creating a short

The gate-to-source path should be very high resistance; a near-zero reading indicates gate oxide breakdown.

In troubleshooting, the term 'sneak path' refers to:

Answer: An unintended current path caused by component failure or design error

A sneak path is an unintended circuit path that allows current to flow in unexpected ways, often causing erratic behavior.

After replacing a faulty component, best practice before applying power is to:

Answer: Verify the replacement part orientation, check for solder bridges, and confirm polarity

Visual inspection for correct orientation, polarity, and solder quality prevents repeat failures caused by installation errors.

A crystal oscillator circuit fails to start oscillating. After confirming the crystal is good, the next most likely suspect is:

Answer: The feedback network capacitors (C1 and C2 in Pierce oscillator)

The Pierce oscillator requires correct feedback capacitor values to sustain oscillation; wrong or failed caps prevent startup.

A technician reads 12V at the input of a 5V linear regulator but only 3.8V at the output under load. The most likely fault is:

Answer: The regulator IC is failing or overheating into thermal shutdown

A linear regulator producing below-nominal output under load is typically failing internally or entering thermal shutdown due to overheating.