ISCET Component-Level Troubleshooting Questions and Answers

Question 1

A technician is troubleshooting a linear DC power supply and observes excessive 60/120 Hz AC ripple on the output using an oscilloscope.
The DC output voltage is present but is lower than specified.
Which component failure is the most likely cause of these symptoms?

Accepted Answer

An open or dried-out main filter capacitor

Answer

A shorted rectifier diode

Answer

An open-circuited transformer primary

Answer

A shorted Zener diode in the regulator section

Question 2

When measuring a 10 kΩ resistor in-circuit with a digital multimeter, the reading is stable at 4.7 kΩ. Assuming the multimeter and the resistor's marked value are correct, what is the most probable explanation for this reading?

Accepted Answer

Another component or circuit path is in parallel with the resistor being measured.

Answer

The multimeter's battery is low, causing an inaccurate reading.

Answer

The resistor has failed and its value has decreased by more than 50%.

Answer

The circuit's power was accidentally left on during the measurement.

Question 3

A technician is signal tracing an audio amplifier. The signal at the collector of Q1 is a clean sine wave with a +5V DC bias. This signal is fed through a coupling capacitor, C2, to the base of Q2. At the base of Q2, the technician measures a distorted sine wave with a +1.5V DC offset. What is the most likely fault?

Accepted Answer

The coupling capacitor (C2) is leaky.

Answer

The coupling capacitor (C2) has failed open.

Answer

The transistor Q2 has a collector-to-emitter short.

Answer

The transistor Q1 is not amplifying correctly.

Question 4

Using a digital multimeter's diode test function to check a known-good NPN Bipolar Junction Transistor (BJT) out-of-circuit, what readings are expected?

Accepted Answer

A forward voltage drop (approx. 0.7V) from the base to the collector and from the base to the emitter, and OL when leads are reversed.

Answer

An open circuit (OL) reading between all three terminals in both directions.

Answer

A low resistance reading between the collector and emitter in both directions, indicating a short.

Answer

A forward voltage drop (approx. 0.7V) from the collector to the base and from the emitter to the base.

Question 5

While signal tracing a common-emitter amplifier stage, a technician confirms a valid AC signal at the transistor's base but finds no AC signal at the collector. A DC voltage measurement at the collector shows it is at the full VCC supply voltage. What is the most probable fault?

Accepted Answer

The collector load resistor is open.

Answer

The transistor is shorted from collector to emitter.

Answer

The emitter resistor is open.

Answer

The coupling capacitor at the input is shorted.

Question 6

An electronic device operates normally but fails intermittently when the chassis is tapped or when it undergoes a significant temperature change. This type of symptom is most characteristic of which fault?

Accepted Answer

A cold solder joint or a hairline crack on the PCB.

Answer

A failed voltage regulator IC.

Answer

An electrolytic capacitor that has lost its capacitance.

Answer

A resistor that has drifted out of tolerance.

A technician is troubleshooting a linear DC power supply and observes excessive 60/120 Hz AC ripple on the output using an oscilloscope.The DC output voltage is present but is lower than specified.Which component failure is the most likely cause of these symptoms?

A technician is troubleshooting a linear DC power supply and observes excessive 60/120 Hz AC ripple on the output using an oscilloscope.
The DC output voltage is present but is lower than specified.
Which component failure is the most likely cause of these symptoms?