ITI Electronics Mechanic Interview Questions and Answers

How do you read the value of a resistor?

From its colour bands: the first bands are digits, the next is the multiplier and the last is the tolerance. For example brown-black-red-gold is 10 × 100 = 1,000 Ω (1 kΩ) at ±5%. Confirm with a multimeter out of circuit.

How to say it: Work one example aloud. It shows you can actually do it.

What is the difference between an electrolytic and a ceramic capacitor?

An electrolytic capacitor has large capacitance and is polarised. It must be fitted the right way round, or it can bulge or burst. A ceramic capacitor has small capacitance and is not polarised.

What does a diode do, and how do you test it?

It lets current flow in one direction only. On the multimeter's diode range, forward bias shows a voltage drop (around 0.6 to 0.7 V for a silicon diode), and reverse bias shows open. Readings both ways mean it is shorted or open.

What is a Zener diode used for?

Voltage regulation. Connected in reverse bias, it holds a nearly constant voltage across it once the Zener voltage is reached.

What are NPN and PNP transistors, and what is a transistor used for?

Both are bipolar transistors with three terminals (emitter, base and collector) differing in which way current flows. A small base current controls a larger collector current, so a transistor is used as an amplifier or as a switch.

What is a rectifier? Explain a bridge rectifier.

A rectifier converts AC to DC. A bridge rectifier uses four diodes so that both halves of the AC cycle reach the load in the same direction, giving full-wave rectified DC, which a filter capacitor then smooths.

What does a voltage regulator IC like the 7805 do?

It gives a steady +5 V output from a higher, unregulated DC input. The 78xx series gives positive fixed voltages, the 79xx series negative ones.

What is an SMPS?

A switched-mode power supply. It switches the input at high frequency and uses a small transformer and feedback control, so it is lighter and more efficient than a linear supply. Common in TVs, computers and chargers.

What are the basic logic gates?

AND, OR, NOT, NAND, NOR, XOR and XNOR. NAND and NOR are called universal gates because any other gate can be built from them.

What can you measure with a multimeter?

Voltage (AC and DC), current, resistance, continuity, and on most meters diode and capacitance checks. Measure resistance and continuity only with the circuit switched off.

What is an oscilloscope used for?

To see a signal's waveform over time (its voltage, frequency and shape), which a multimeter cannot show. It is used to trace signals and find where a waveform goes wrong.

What makes a good solder joint?

Clean surfaces, the right iron temperature, enough solder to form a smooth, shiny cone around the lead, and no bridges to the next pad. A dull, lumpy joint is a dry joint and causes intermittent faults.

How to say it: Mention "dry joint". It is the fault supervisors see most.

How do you remove and replace an SMD component?

With a hot-air rework station at the right temperature and airflow, lifting the part with tweezers once the solder melts, cleaning the pads with flux and solder wick, then placing and reflowing the new part.

What is ESD and how do you prevent it?

Electrostatic discharge: static from your body can damage ICs without any visible sign. Wear an earthed wrist strap, work on an ESD mat, and handle boards by the edges in ESD-safe bags.

A device does not power on. How will you find the fault?

Check the input supply and fuse first, then the power supply section (rectifier diodes, filter capacitor, regulator output) with a multimeter, then follow the supply rails to the board. Look for burnt components and bulged capacitors on the way.

What is the usual practical test?

Identifying and testing components, soldering a small circuit such as a power supply or LED driver on a PCB, measuring voltages at test points, or finding a fault in a given board.

How to say it: Keep the work area tidy and wear the wrist strap: both are watched.