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UPMSP High School Mobile-Phone Repair - Code 980 study materials
UPMSP High School Mobile-Phone Repair - Code 980 study resources

UPMSP High School Mobile-Phone Repair - Code 980 practice questions

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Question 1Safety, Tools and Workshop Practice

A mobile phone technician is about to open a smartphone that contains a lithium-ion battery. Which precaution is most important before starting disassembly?

  1. Power the phone off completely and avoid puncturing or bending the battery Correct answer.
  2. Remove the SIM tray only after the back cover has been unscrewed
  3. Place the phone on a soft cloth to protect the screen from scratches
  4. Charge the battery fully so that the phone stays on during the repair

Explanation

A lithium-ion battery that is punctured, crushed, or shorted can vent hot gas and catch fire, so the device must be powered down and the cell handled without pressure or deformation. Fully charging the pack before service increases stored energy and makes any accidental damage more dangerous. Screen protection and SIM removal are useful steps but do not address the main hazard.

Question 2Safety, Tools and Workshop Practice

Which tool is designed to measure the DC voltage of a phone battery connector during diagnosis?

  1. A hot-air rework station
  2. An ultrasonic cleaner
  3. A precision screwdriver set
  4. A digital multimeter Correct answer.

Explanation

A digital multimeter in DC voltage mode measures potential difference across the battery connector and lets the technician confirm whether the pack or the charging circuit is supplying power. Hot-air stations, ultrasonic cleaners, and screwdrivers perform mechanical or thermal tasks and cannot report voltage.

Question 3Safety, Tools and Workshop Practice

A technician must store a small container of isopropyl alcohol in the workshop. Which practice best follows good workshop safety?

  1. Store it in an open tray near the soldering station for quick access
  2. Pour it into an unlabelled bottle to save space on the bench
  3. Keep it beside the hot-air nozzle so that it warms before use
  4. Keep it in a closed labelled container away from heat sources and open flames Correct answer.

Explanation

Isopropyl alcohol is flammable and volatile, so it must be kept in a closed, clearly labelled container away from ignition sources such as soldering irons and hot-air nozzles. Open trays allow vapour to accumulate, and unlabelled bottles create a risk of mistaken identity. Proximity to heat directly increases the fire hazard.

Question 4Safety, Tools and Workshop Practice

When soldering a wire to a charging-port pad, which combination of conditions produces a reliable joint?

  1. Correct iron tip temperature, clean tinned surfaces, and a brief contact time Correct answer.
  2. No flux and a heavily oxidised pad
  3. Maximum iron temperature with prolonged heating of the pad
  4. A cold iron held on the joint for several minutes

Explanation

A sound solder joint needs enough heat to melt the alloy, clean oxide-free surfaces with flux, and short contact so that components and pads are not damaged. Excessive temperature or long dwell times lift pads and damage plastic connectors. Oxide and missing flux prevent wetting, and a cold iron never reaches soldering temperature.

Question 5Safety, Tools and Workshop Practice

Which personal protective equipment is most appropriate when using an ultrasonic cleaner with a cleaning solvent?

  1. Ear defenders only
  2. A grounding wrist strap only
  3. Safety goggles and suitable gloves Correct answer.
  4. A dust mask only

Explanation

Solvent splash and vapour are the main hazards of ultrasonic cleaning, so eye protection and chemically resistant gloves are the key controls. A dust mask does not stop solvent vapour, ear defenders address noise only, and an anti-static strap protects electronics from static rather than the operator from chemicals.

Question 6Safety, Tools and Workshop Practice

A technician notices a frayed live wire on the bench power supply cable. What is the correct immediate action?

  1. Turn the supply off at its own switch and keep using the cable
  2. Wrap the frayed section with adhesive tape and continue working
  3. Stop using the unit, disconnect it from the mains, and tag it for repair Correct answer.
  4. Continue using it but keep hands away from the damaged part

Explanation

Damaged mains insulation is a shock and fire hazard, so the equipment must be taken out of service, isolated from the supply, and marked so nobody else plugs it in. Taping or working around the damage leaves the hazard present, and switching off only the unit does not remove mains potential from a damaged cable.

Question 7Safety, Tools and Workshop Practice

Why should a technician wear an anti-static wrist strap when handling a bare logic board?

  1. It keeps the board cool during testing
  2. It drains static charge from the body so that sensitive chips are not damaged Correct answer.
  3. It protects the technician from mains electric shock
  4. It measures the current flowing through the board

Explanation

Static electricity built up on the body can discharge into a board and destroy or degrade integrated circuits, and a wrist strap with a suitable resistor safely bleeds that charge to ground. The strap is not a shock-protection device for mains voltage, does not measure current, and has no cooling function.

Question 8Safety, Tools and Workshop Practice

A phone shows no charging and the technician measures about 5 V at the charging-port pins but no voltage reaching the battery connector. Which diagnostic step is most logical next?

  1. Replace the battery immediately without further measurement
  2. Reflash the phone firmware and retest
  3. Clean the speaker grille and retest
  4. Trace continuity from the port through the charging IC to the battery connector Correct answer.

Explanation

Voltage present at the port but absent at the battery connector points to a break in the charging path, such as the charging IC, a protection component, or a track, so continuity tracing localises the fault. Replacing the battery cannot fix a missing supply, firmware does not create voltage, and speaker cleaning is unrelated.

Question 9Safety, Tools and Workshop Practice

Which practice correctly protects a phone's flex cables during disassembly?

  1. Fold the flex sharply to keep it out of the way
  2. Lift connectors straight up with a plastic spudger and avoid sharp metal levers near the flex Correct answer.
  3. Pry connectors with a metal screwdriver for extra leverage
  4. Pull the flex cable firmly until the adhesive releases

Explanation

Flex cables and board connectors are fragile, so they should be released vertically with a non-conductive plastic tool that will not short or scratch nearby parts. Metal levers concentrate force and can tear tracks or bridge contacts, pulling damages the connector, and sharp folds crack the conductive traces.

Question 10Safety, Tools and Workshop Practice

A technician needs to remove a small BGA shield cover held by lead-free solder. Which approach is safest for the board?

  1. Chip the cover off with a chisel and hammer
  2. Heat the board in an oven at maximum temperature for a long period
  3. Use controlled hot air with flux and even heating, then lift the part gently Correct answer.
  4. Use a large flame torch directly on the board

Explanation

Lead-free solder needs a controlled, even heat source with flux to melt properly, and gentle lifting avoids pulling pads. A torch, chisel, or uncontrolled oven heating creates localised overheating, pad lift, and board warpage that can destroy the assembly.

Question 11Safety, Tools and Workshop Practice

Which action best prevents cross-contamination when cleaning a phone that arrived with liquid damage?

  1. Use fresh cleaning materials and dispose of contaminated swabs safely Correct answer.
  2. Blow compressed air directly into the ear speaker
  3. Rinse the board under a running tap
  4. Reuse the same swab on several phones to save materials

Explanation

Liquid-damaged devices may carry corrosive residue and biological contamination, so fresh materials and safe disposal of used swabs prevent spreading contamination to other devices and to the technician. Reusing swabs transfers residue, tap water adds minerals and corrosion, and blowing air drives contaminants deeper into the speaker.

Question 12Safety, Tools and Workshop Practice

A technician is choosing a screwdriver for the tiny Phillips screws that hold a phone's internal bracket. What is the correct selection rule?

  1. Use the largest driver that fits loosely in the recess
  2. Use a flat-blade driver on any screw head
  3. Use a driver one size smaller so it enters easily
  4. Match the driver tip size and type exactly to the screw head Correct answer.

Explanation

A driver that matches the head size and type transmits torque across the full recess and avoids cam-out, which rounds the screw head. Oversized tips do not seat properly, flat blades damage cross-head screws, and undersized tips slip and strip the recess.

Question 13Safety, Tools and Workshop Practice

What is the main reason for keeping a workbench free of loose metal screws and offcuts while a phone board is powered?

  1. Metal pieces improve heat dissipation from the board
  2. Metal offcuts attract dust to the display
  3. Loose screws increase the phone's weight
  4. Loose metal can bridge contacts and cause short circuits Correct answer.

Explanation

Conductive debris on a live board can bridge adjacent pads or components and create short circuits that destroy the circuit. Dust attraction, weight, and heat dissipation are not credible reasons, and the short-circuit risk is the genuine safety and reliability concern.

Question 14Safety, Tools and Workshop Practice

A lithium-ion pouch battery has begun to swell inside a phone. What is the correct handling procedure?

  1. Puncture the pouch to release the pressure before removal
  2. Store the swollen battery in a drawer with other spare parts
  3. Stop work, isolate the device, and place the battery in a fire-resistant container for safe disposal Correct answer.
  4. Press the battery flat and continue the repair

Explanation

A swollen cell is mechanically unstable and can rupture, vent, or ignite, so work should stop and the pack isolated in a fire-resistant container for proper disposal. Puncturing releases flammable electrolyte, pressing can rupture the pouch, and storing it with other parts puts the whole stock at risk.

Question 15Safety, Tools and Workshop Practice

Which measurement confirms that a charger is delivering power to a phone's charging port?

  1. Resistance across the loudspeaker coil
  2. Continuity of the vibration motor leads
  3. DC voltage at the port contacts with the charger connected Correct answer.
  4. Capacitance of the display backlight circuit

Explanation

Measuring DC volts at the port contacts while the charger is connected directly shows whether supply reaches the phone. Speaker resistance, backlight capacitance, and motor continuity test unrelated circuits and cannot confirm charger output.

Question 16Safety, Tools and Workshop Practice

Why is a temperature-controlled soldering station preferred over a simple mains iron for phone board rework?

  1. It works without any electrical supply
  2. It holds a set tip temperature, reducing the risk of pad lift and heat damage Correct answer.
  3. It automatically removes solder from the joint
  4. It cools the board below room temperature

Explanation

Phone boards use small pads and heat-sensitive plastics, so a station that regulates tip temperature lets the technician apply just enough heat for a short time. A basic iron swings in temperature and overheats joints. No soldering iron works without power, removes solder by itself, or cools the board.

Question 17Safety, Tools and Workshop Practice

A technician must test a phone board that has been removed from its case. Which setup best reduces the risk of accidental short circuits during the test?

  1. Hold the board in one hand while probing with the other
  2. Place the board on a non-conductive stand with only the required connectors attached Correct answer.
  3. Rest the board on a sheet of aluminium foil
  4. Lay the board directly on the metal bench top

Explanation

A non-conductive support keeps the underside of the board clear of metal that could bridge contacts, and attaching only the needed connectors limits accidental shorts. A metal bench, foil, or hand-holding exposes the board to conductive surfaces and uncontrolled movement.

Question 18Safety, Tools and Workshop Practice

A phone draws abnormally high current as soon as it is connected to a bench supply, even before the power button is pressed. Which interpretation and action are most appropriate?

  1. Assume the battery is simply old and fit a new one
  2. Conclude that the display is faulty and replace it
  3. Suspect a short on a main power rail; isolate sections and check for a low-resistance path before applying power again Correct answer.
  4. Increase the supply current limit and continue testing

Explanation

Excessive current before the phone is switched on indicates a short or leak on a supply rail, so the technician should limit current, isolate sections, and look for a low-resistance path rather than feeding more energy into the fault. A battery swap, a higher current limit, or a display replacement does not address a rail short and may cause further damage.

Question 19Safety, Tools and Workshop Practice

A workshop uses both leaded and lead-free solder. Which control is most important for the technician's health?

  1. Store solder reels in an open box on the bench
  2. Keep the bench fan blowing fumes towards the face
  3. Avoid eating or smoking at the bench, wash hands after work, and use fume extraction Correct answer.
  4. Work faster so that exposure time is shorter

Explanation

Solder fume and lead contamination enter the body mainly by inhalation and ingestion, so fume extraction plus hand washing and no eating at the bench are the key controls. Working faster does not reduce exposure, directing fumes at the face increases it, and open storage adds contamination and oxidation.

Question 20Safety, Tools and Workshop Practice

A technician suspects a phone's charging fault is caused by a damaged USB-C receptacle whose pins are bent and touching. What is the most defensible repair decision?

  1. Leave the damaged receptacle and rely on wireless charging only
  2. Replace the receptacle with the correct part and verify pin continuity before powering the phone Correct answer.
  3. Bridge the bent pins together with solder to restore contact
  4. Straighten the pins with a needle while the charger is connected

Explanation

A receptacle with bent, touching pins can short the supply and data lines, so the correct fix is replacement with the specified part followed by continuity checks before power is applied. Straightening live pins risks a short, ignoring the fault leaves a hazard, and bridging pins creates a permanent short.

Question 21Basic Electronics and Electrical Fundamentals

In a mobile phone repair workshop, which instrument is used to measure the potential difference between two points of a circuit without breaking the connection?

  1. Ohmmeter connected across the supply
  2. Ammeter connected in series
  3. Voltmeter connected in parallel Correct answer.
  4. Megger connected in series

Explanation

A voltmeter measures potential difference and must be connected in parallel with the component so that it taps the voltage while drawing very little current. An ammeter, by contrast, is inserted in series to measure current flow.

Question 22Basic Electronics and Electrical Fundamentals

A resistor of 220 Ω carries a current of 0.05 A. What is the voltage drop across it?

  1. 0.23 V
  2. 11 V Correct answer.
  3. 44 V
  4. 4.4 V

Explanation

Ohm's law states V = I × R, so multiplying 0.05 A by 220 Ω gives 11 V. This is a typical calculation when checking a current-sense resistor path on a phone board.

Question 23Basic Electronics and Electrical Fundamentals

Which property of a capacitor allows it to block direct current while passing alternating current in a phone's audio filter circuit?

  1. It stores charge as a magnetic field
  2. Its resistance rises with temperature
  3. It converts AC into DC permanently
  4. Its reactance falls as frequency rises Correct answer.

Explanation

Capacitive reactance is inversely proportional to frequency (Xc = 1/2πfC), so at high frequencies the reactance is low and the capacitor passes AC, while at zero frequency it blocks DC. This is why coupling capacitors separate bias from signal.

Question 24Basic Electronics and Electrical Fundamentals

A phone battery is marked 3.85 V and 4000 mAh. What does the 4000 mAh rating express?

  1. The maximum charging current
  2. The internal resistance of the cell
  3. The charge capacity of the cell Correct answer.
  4. The energy stored in watt-hours

Explanation

Milliampere-hour is a unit of electric charge: 4000 mAh means the cell can deliver 4000 mA for one hour. Energy in watt-hours would require multiplying by the nominal voltage.

Question 25Basic Electronics and Electrical Fundamentals

In a phone charging circuit, two resistors of 100 Ω and 100 Ω are connected in parallel. What is the equivalent resistance?

  1. 200 Ω
  2. 50 Ω Correct answer.
  3. 100 Ω
  4. 25 Ω

Explanation

For two equal resistors in parallel the equivalent is half of one value, so 100 Ω in parallel with 100 Ω gives 50 Ω. The general formula 1/R = 1/R1 + 1/R2 confirms this result.

Question 26Basic Electronics and Electrical Fundamentals

Which material is used for the semiconductor substrate of most mobile phone integrated circuits?

  1. Graphite
  2. Silicon Correct answer.
  3. Copper
  4. Aluminium

Explanation

Silicon is the standard semiconductor material for integrated circuits because its oxide forms a stable insulating layer and its doping behaviour is well controlled. Copper and aluminium are used as conductors, not as the substrate.

Question 27Basic Electronics and Electrical Fundamentals

Which safety practice is mandatory before soldering or desoldering components on a phone mainboard?

  1. Work on a carpeted surface to cushion the board
  2. Disconnect the battery connector and use an ESD-safe bench Correct answer.
  3. Hold the board with bare fingers for stability
  4. Increase the iron temperature to the maximum

Explanation

Disconnecting the battery prevents short circuits during work, and an ESD-safe bench with a wrist strap protects sensitive ICs from static discharge. High iron temperatures and carpeted surfaces increase the risk of damage.

Question 28Basic Electronics and Electrical Fundamentals

A 5 V supply feeds a series circuit of 1 kΩ and 3 kΩ. What is the current flowing through the 3 kΩ resistor?

  1. 1.25 mA Correct answer.
  2. 2.5 mA
  3. 0.8 mA
  4. 5 mA

Explanation

The total series resistance is 4 kΩ, so I = V/R = 5/4000 = 1.25 mA, and the same current flows through both resistors in series. Series elements always share identical current.

Question 29Basic Electronics and Electrical Fundamentals

A silicon diode in a phone's charging protection path is forward biased. What is its approximate voltage drop?

  1. 1.4 V
  2. 5.0 V
  3. 0.7 V Correct answer.
  4. 0.2 V

Explanation

A forward-biased silicon p-n junction drops about 0.6 to 0.7 V, which is the barrier potential of silicon. Germanium diodes drop about 0.2 to 0.3 V, and 1.4 V would correspond to two silicon junctions in series.

Question 30Basic Electronics and Electrical Fundamentals

A capacitor marked 104 is used in a phone circuit. What is its value?

  1. 100 nF Correct answer.
  2. 104 pF
  3. 0.104 µF
  4. 10 nF

Explanation

In the three-digit code, the first two digits give the significant figures and the third gives the number of zeros in picofarads, so 104 means 10 followed by four zeros, i.e. 100000 pF or 100 nF. This equals 0.1 µF.

Question 31Basic Electronics and Electrical Fundamentals

Why is a Schottky diode often preferred over a standard silicon diode in a phone's power path?

  1. It works only with alternating current
  2. It has a lower forward voltage drop and switches faster Correct answer.
  3. It blocks higher reverse voltage than any other diode
  4. It stores charge like a capacitor

Explanation

A metal-semiconductor Schottky junction has a forward drop of roughly 0.2 to 0.3 V and very short reverse recovery, which reduces losses and improves efficiency in switching supplies. The lower drop matters when the battery rail is only a few volts.

Question 32Basic Electronics and Electrical Fundamentals

In a common-emitter transistor stage used as a switch in a phone board, which condition drives the transistor into saturation?

  1. Base current large enough to make collector current limited by the load Correct answer.
  2. Zero base current with collector voltage applied
  3. Collector-emitter junction forward biased alone
  4. Base-emitter junction reverse biased

Explanation

Saturation occurs when enough base current is supplied so that the collector current is limited by the external load rather than by the transistor, leaving a small collector-emitter voltage. In this state the device behaves almost like a closed switch.

Question 33Basic Electronics and Electrical Fundamentals

A phone's lithium-ion cell reads 3.0 V on a multimeter. What does this indicate about the cell state?

  1. Overcharged beyond its limit
  2. Deeply discharged and requiring careful pre-charge Correct answer.
  3. Shorted internally and unusable
  4. Fully charged and ready for use

Explanation

A lithium-ion cell at about 3.0 V is near or below its normal discharge cutoff, so it should be charged with a low pre-charge current before normal charging. Charging a deeply discharged cell at full current can cause damage or heating.

Question 34Basic Electronics and Electrical Fundamentals

What is the purpose of a decoupling capacitor placed close to an IC power pin on a phone mainboard?

  1. To convert the DC supply into AC
  2. To provide a low-impedance path for high-frequency current and stabilise the supply Correct answer.
  3. To limit the maximum current drawn by the IC
  4. To increase the DC voltage supplied to the IC

Explanation

A decoupling capacitor acts as a local charge reservoir and shunts high-frequency noise to ground, keeping the supply rail steady during fast switching. Placing it close to the pin minimises trace inductance.

Question 35Basic Electronics and Electrical Fundamentals

A resistor has colour bands brown, black, red, gold. What is its value and tolerance?

  1. 10 kΩ ±5%
  2. 1 kΩ ±10%
  3. 100 Ω ±5%
  4. 1 kΩ ±5% Correct answer.

Explanation

Brown is 1, black is 0, red is a multiplier of 100, giving 10 × 100 = 1000 Ω, and gold indicates ±5% tolerance. Reading the multiplier band as a zero count is the standard four-band convention.

Question 36Basic Electronics and Electrical Fundamentals

Why must an ammeter never be connected directly across a battery in a phone circuit?

  1. Its high internal resistance would stop all current flow
  2. It would reverse the battery polarity
  3. Its very low internal resistance would cause a large current and possible damage Correct answer.
  4. It would measure voltage instead of current

Explanation

An ideal ammeter has almost zero resistance so that it does not disturb the circuit, which means connecting it across a source creates a near short circuit and a dangerously high current. Ammeters must always be inserted in series with the load.

Question 37Basic Electronics and Electrical Fundamentals

A phone board draws 0.4 A from a 4.2 V battery rail. What power is being consumed?

  1. 10.5 W
  2. 4.6 W
  3. 0.095 W
  4. 1.68 W Correct answer.

Explanation

Electrical power is the product of voltage and current, so 4.2 V × 0.4 A = 1.68 W. This relationship is used when estimating heat dissipation and battery drain in a phone.

Question 38Basic Electronics and Electrical Fundamentals

A coil of wire in a phone's wireless charging circuit produces a changing magnetic field. Which principle explains the voltage induced in a nearby receiver coil?

  1. Thermionic emission
  2. Electrostatic attraction
  3. Electromagnetic induction Correct answer.
  4. Photoelectric effect

Explanation

A changing magnetic flux through a coil induces an electromotive force according to Faraday's law, which is the basis of wireless power transfer. The receiver coil converts the changing flux back into an alternating voltage.

Question 39Basic Electronics and Electrical Fundamentals

A technician measures 0 V across a resistor that should drop 1.2 V while the circuit is powered. Which interpretation is most reasonable?

  1. The resistor is dissipating maximum power
  2. No current is flowing through that resistor or the measurement point is open Correct answer.
  3. The multimeter battery is always the cause
  4. The resistor value has increased to infinity

Explanation

By Ohm's law, a zero voltage drop across a resistor implies zero current through it, which points to an open path or a poor probe contact. Checking continuity and probe placement confirms which cause applies.

Question 40Basic Electronics and Electrical Fundamentals

In a phone mainboard, a rail is labelled 1.8 V and feeds a sensor drawing 20 mA. How much power does the sensor consume?

  1. 36 mW Correct answer.
  2. 90 mW
  3. 0.9 W
  4. 0.036 mW

Explanation

Power equals voltage times current, so 1.8 V × 0.020 A = 0.036 W, which is 36 mW. Keeping units consistent in amperes and volts avoids decimal errors.

Question 41Basic Electronics and Electrical Fundamentals

Two resistors of 6 Ω and 3 Ω are connected in parallel across a 6 V source. What current flows from the source?

  1. 3 A Correct answer.
  2. 2 A
  3. 1 A
  4. 0.67 A

Explanation

The parallel equivalent is (6 × 3)/(6 + 3) = 2 Ω, and the total current is 6 V / 2 Ω = 3 A. Alternatively, branch currents of 1 A and 2 A add to 3 A.

Question 42Basic Electronics and Electrical Fundamentals

A phone shows no charging and the charging port measures 5 V on VBUS but the battery rail stays at 3.7 V with no rise. Which fault is most consistent with these readings?

  1. A shorted battery that is clamping the rail
  2. A weak Wi-Fi antenna
  3. An open circuit in the charging path between VBUS and the battery charger IC output Correct answer.
  4. A faulty display connector

Explanation

Presence of 5 V on VBUS shows the cable and port are delivering power, while an unchanged battery rail suggests the charge path is interrupted before reaching the cell. Continuity and component checks along that path localise the open.

Question 43Basic Electronics and Electrical Fundamentals

A transistor in a phone board is found with both junctions reverse biased when the control signal is high. What does this indicate?

  1. The device is acting as a capacitor
  2. The device is operating as a linear amplifier
  3. The device is saturated and conducting heavily
  4. The device is in cutoff and the drive signal is not reaching the base Correct answer.

Explanation

With both junctions reverse biased the transistor is in cutoff, so no collector current flows even though the control signal should turn it on. This points to a break in the base drive path or a failed device.

Question 44Basic Electronics and Electrical Fundamentals

A 4000 mAh battery powers a phone that draws an average of 500 mA. Approximately how long will it run, ignoring losses?

  1. 4 hours
  2. 8 hours Correct answer.
  3. 2 hours
  4. 20 hours

Explanation

Dividing capacity by average current gives 4000 mAh / 500 mA = 8 hours. Real runtime is shorter because of conversion losses and because capacity is rated at a specific discharge rate.

Question 45Mobile Phone Hardware Architecture and Components

A mobile phone's power management IC (PMIC) is best described as the component that:

  1. converts and regulates battery voltage into the multiple rails the phone's subsystems require Correct answer.
  2. stores the operating system image between power cycles
  3. amplifies radio-frequency signals before they reach the antenna
  4. converts digital image data into signals for the display panel

Explanation

The PMIC takes the raw battery voltage and generates regulated, sequenced supply rails (for example core, memory, camera and display rails) needed by the phone's chips. It also manages charging and power sequencing at boot. It does not store firmware, amplify RF, or drive the display.

Question 46Mobile Phone Hardware Architecture and Components

In a typical smartphone, the component responsible for executing the operating system and application code is the:

  1. antenna switch module
  2. baseband processor
  3. application processor (SoC) Correct answer.
  4. NAND flash memory

Explanation

The application processor, usually part of a system-on-chip, runs the operating system, user applications and graphics workloads. The baseband handles cellular protocol processing, flash stores data, and the antenna switch routes RF paths.

Question 47Mobile Phone Hardware Architecture and Components

Which memory type in a phone loses its contents when power is removed and is used as working memory for the running OS?

  1. eMMC flash
  2. LPDDR SDRAM Correct answer.
  3. UFS flash
  4. EEPROM

Explanation

LPDDR SDRAM is volatile working memory that holds the running OS and active application data, so it clears on power loss. eMMC, UFS and EEPROM are non-volatile and retain data without power.

Question 48Mobile Phone Hardware Architecture and Components

The primary function of the antenna in a mobile handset is to:

  1. convert analogue audio into digital PCM samples
  2. transduce electrical RF signals into electromagnetic waves and vice versa Correct answer.
  3. rectify alternating current from the charger into direct current
  4. regulate the charging current delivered to the battery

Explanation

An antenna is a transducer that converts guided electrical RF energy from the transceiver into radiated electromagnetic waves, and captures incoming waves back into electrical signals. Rectification, charging regulation and audio digitisation belong to other circuits.

Question 49Mobile Phone Hardware Architecture and Components

A phone's camera module fails to focus at any distance and the lens assembly does not move. Which component inside the module should be suspected first?

  1. the flex connector's shielding foil
  2. the image sensor's colour filter array
  3. the IR-cut filter glass
  4. the voice-coil motor (VCM) autofocus actuator Correct answer.

Explanation

Autofocus movement is produced by a voice-coil motor that shifts the lens barrel under magnetic force. If the lens never moves, the actuator or its driver circuit is the prime suspect. The sensor, IR-cut filter and shielding do not create mechanical focus motion.

Question 50Mobile Phone Hardware Architecture and Components

Which statement correctly distinguishes an LCD from an OLED display panel in a handset?

  1. OLED pixels emit their own light, while LCD pixels rely on a backlight Correct answer.
  2. LCD pixels emit their own light, while OLED pixels require a separate backlight
  3. OLED panels cannot display colour images
  4. LCD panels contain no polarising filters

Explanation

OLED sub-pixels are self-emissive organic diodes, so black areas can switch off completely. LCD pixels only modulate light, so they need a backlight plus polarisers. Both technologies display full colour.