Question 1(a) [3 marks]

Explain different types of maintenance in brief.

Answer:

Type of Maintenance	Description
Preventive Maintenance	Scheduled regular inspection and servicing to prevent breakdowns
Corrective Maintenance	Repairs performed after equipment failure to restore functionality
Predictive Maintenance	Uses condition monitoring to predict when maintenance will be needed

Mnemonic: "PCPro" - Preventive prevents, Corrective cures, Predictive predicts

Question 1(b) [4 marks]

Explain maintenance procedure of Washing Machine.

Answer:

Maintenance Procedure for Washing Machine:

flowchart LR
    A[Regular Inspection] --> B[Clean Filter]
    B --> C[Check Hoses]
    C --> D[Balance Load]
    D --> E[Clean Drum]

Filter Cleaning: Remove and clean lint filter monthly
Hose Inspection: Check for cracks and leaks every 3 months
Load Distribution: Ensure proper balancing to prevent vibration
Drum Cleaning: Run empty hot water cycle with vinegar quarterly

Mnemonic: "FHLD" - Filters, Hoses, Loads, Drum need regular attention

Question 1(c) [7 marks]

Explain maintenance and troubleshooting procedure of Microwave Oven.

Answer:

Maintenance and Troubleshooting for Microwave Oven:

Maintenance Task	Procedure	Frequency
External Cleaning	Wipe with mild detergent	Weekly
Internal Cleaning	Clean food particles and grease	After each spill
Door Seal Check	Inspect for damage or leakage	Monthly
Ventilation Check	Ensure vents are unobstructed	Monthly

Troubleshooting Procedure:

flowchart TD
    A[No Power] -->|Check| B[Power Connection]
    C[Not Heating] -->|Check| D[Door Switch & Magnetron]
    E[Uneven Cooking] -->|Check| F[Turntable Mechanism]
    G[Sparking] -->|Check| H[Metal Objects/Damaged Cavity]
    I[Unusual Noise] -->|Check| J[Fan & Turntable Motor]

Power Issues: Check fuse, circuit breaker, and cord
Heating Problems: Test door switch, high voltage capacitor, magnetron
Safety First: Never operate with damaged door or seals

Mnemonic: "POWER" - Power, Oven interior, Wiring, Electronics, Radiation seals

Question 1(c OR) [7 marks]

Explain maintenance and troubleshooting procedure of projector.

Answer:

Maintenance and Troubleshooting for Projector:

Maintenance Task	Procedure	Frequency
Lens Cleaning	Use lens cloth and solution	Monthly
Filter Cleaning	Remove and clean dust	Every 100 hours
Lamp Inspection	Check for discoloration/dimming	Every 300 hours
Ventilation	Ensure proper airflow	Before each use

Troubleshooting Procedure:

flowchart TD
    A[No Power] -->|Check| B[Power Supply & Cable]
    C[No Image] -->|Check| D[Source Connection & Input Selection]
    E[Poor Image] -->|Check| F[Focus & Lens]
    G[Overheating] -->|Check| H[Ventilation & Filters]
    I[Lamp Failure] -->|Check| J[Lamp Life & Replacement]

Image Issues: Adjust focus, resolution, keystone correction
Lamp Problems: Check lamp hours, replace if exceeding limit
Connectivity: Verify input source and cable connections
Thermal Issues: Clean filters and ensure proper ventilation

Mnemonic: "FLAMVE" - Filters, Lamp, Airflow, Mounting, Voltage, Environment

Question 2(a) [3 marks]

Explain the terms in brief: (1) Hue (2) Brightness

Answer:

Term	Description
Hue	The pure color attribute that distinguishes colors (red, green, blue, etc.) based on light wavelength
Brightness	The amount of light emitted or reflected from a color, determining how light or dark it appears

Diagram:

             Hue
          (Color Type)
              ↑
              |
Saturation ←--+--→ Brightness
(Intensity)   |   (Lightness)
              ↓
            Value

Mnemonic: "HB-WC" - Hue determines What Color, Brightness determines White-to-black level

Question 2(b) [4 marks]

Write a short note on LCD TV.

Answer:

LCD TV Technology:

flowchart LR
    A[Backlight] --> B[Polarizing Filter]
    B --> C[Liquid Crystal Layer]
    C --> D[Color Filter]
    D --> E[Screen]

Working Principle: Uses liquid crystals that twist/untwist to allow/block light
Key Components: Backlight, polarizing filters, liquid crystal matrix, color filters
Advantages: Thin profile, energy efficient, no radiation, sharp image
Limitations: Limited viewing angle, slower response time than newer technologies

Mnemonic: "BPLCS" - Backlight Passes Light through Crystals to Screen

Question 2(c) [7 marks]

Draw and explain block diagram of DTH receiver.

Answer:

DTH Receiver Block Diagram:

flowchart LR
    A[Satellite Dish] --> B[LNB]
    B --> C[Tuner]
    C --> D[Demodulator]
    D --> E[MPEG Decoder]
    E --> F[Video/Audio Processor]
    F --> G[TV Display]
    H[Smart Card] --> I[Conditional Access Module]
    I --> D
    J[User Interface] --> K[Microcontroller]
    K --> C
    K --> E

Satellite Dish: Captures signals from satellite
LNB (Low Noise Block): Converts high frequency signals to lower frequency
Tuner: Selects specific channel frequency
Demodulator: Extracts digital information from carrier signal
MPEG Decoder: Decompresses video/audio data
Conditional Access Module: Controls subscription access
Microcontroller: Controls overall operation and user inputs

Mnemonic: "SLTDMP" - Satellite, LNB, Tuner, Demodulator, MPEG, Processor

Question 2(a OR) [3 marks]

Explain the terms in brief: (1) Luminance (2) chrominance

Answer:

Term	Description
Luminance	The brightness or intensity component of a video signal (Y) that carries black and white information
Chrominance	The color component of a video signal (Cb, Cr) that carries hue and saturation information

Diagram:

Video Signal
    |
    +----------+----------+
    |                     |
Luminance (Y)      Chrominance (C)
(Brightness)         /         \
                    /           \
                   /             \
            Blue-Y (Cb)       Red-Y (Cr)
            (Blue diff)       (Red diff)

Mnemonic: "LC-BH" - Luminance controls Brightness, Chrominance controls Hue

Question 2(b OR) [4 marks]

Explain Grassman's law.

Answer:

Grassman's Laws of Color Mixing:

Law	Description
Symmetry	If color A matches color B, then B matches A
Proportionality	If A matches B, then nA matches nB (for any intensity n)
Additivity	If A matches B and C matches D, then A+C matches B+D

Application: Forms the basis of RGB color model in displays
Significance: Allows creating any color by mixing three primary colors
Limitation: Applies only to light (additive mixing), not pigments

Mnemonic: "SPA Color" - Symmetry, Proportionality, Additivity laws for Color matching

Question 2(c OR) [7 marks]

Draw and explain block diagram of colour TV receiver.

Answer:

Colour TV Receiver Block Diagram:

flowchart LR
    A[Antenna] --> B[Tuner]
    B --> C[IF Amplifier]
    C --> D[Video Detector]
    D --> E[Video Amplifier]
    E --> F[Color Processor]
    F --> G[RGB Matrix]
    G --> H[Picture Tube/Display]
    D --> I[Sound IF]
    I --> J[Sound Demodulator]
    J --> K[Audio Amplifier]
    K --> L[Speaker]
    M[Sync Separator] --> N[Deflection Circuits]
    N --> H
    D --> M

Tuner: Selects desired channel frequency
IF Amplifier: Amplifies intermediate frequency signals
Video Detector: Extracts video and audio information
Color Processor: Separates luminance and chrominance
RGB Matrix: Converts color signals to red, green, blue
Sync Separator: Extracts horizontal and vertical sync
Deflection Circuits: Control electron beam scanning

Mnemonic: "TIVCRDS" - Tuner, IF, Video, Color, RGB, Deflection, Speaker

Question 3(a) [3 marks]

State main components of solar power system and specifications of solar power system.

Answer:

Main Components of Solar Power System:

Component	Function
Solar Panels	Convert sunlight to electricity
Charge Controller	Regulates battery charging
Battery Bank	Stores electrical energy
Inverter	Converts DC to AC electricity
Mounting Structure	Supports and positions panels

Specifications:

Panel Rating: 100-400W per panel
Battery Capacity: 100-200Ah
Inverter Rating: 500-5000W
System Voltage: 12/24/48V

Mnemonic: "SCBIM" - Solar panels, Controller, Battery, Inverter, Mounting

Question 3(b) [4 marks]

List types, applications and technical specifications of microwave oven.

Answer:

Types of Microwave Ovens:

Type	Features
Solo	Basic heating and defrosting only
Grill	Additional grilling element
Convection	Has heating element and fan for baking
Combination	Integrates microwave, grill and convection

Applications:

Food reheating
Defrosting
Cooking
Baking (convection models)

Technical Specifications:

Power: 700-1200 Watts
Capacity: 20-40 Liters
Frequency: 2.45 GHz
Voltage: 220-240V AC

Mnemonic: "SGCC" - Solo, Grill, Convection, Combo ovens for various cooking needs

Question 3(c) [7 marks]

Explain working of Air conditioner and Refrigerator

Answer:

Working Principle of Air Conditioner and Refrigerator:

flowchart LR
    A[Compressor] -->|High pressure hot gas| B[Condenser]
    B -->|High pressure liquid| C[Expansion Valve]
    C -->|Low pressure liquid| D[Evaporator]
    D -->|Low pressure gas| A

Common Components:

Compressor: Pressurizes refrigerant gas
Condenser: Releases heat, converts gas to liquid
Expansion Valve: Reduces pressure of liquid refrigerant
Evaporator: Absorbs heat, converts liquid to gas

Differences:

Aspect	Air Conditioner	Refrigerator
Purpose	Cools entire room	Maintains cold in insulated cabinet
Temperature	18-26°C typically	2-8°C (fridge), -18°C (freezer)
Control	Thermostat with remote	Manual or digital thermostat

Mnemonic: "CEVA" - Compression, Expansion, Vaporization, Absorption cycle

Question 3(a OR) [3 marks]

List technical specifications of Air conditioner and Refrigerator

Answer:

Technical Specifications:

Specification	Air Conditioner	Refrigerator
Cooling Capacity	1-2 ton (12,000-24,000 BTU)	100-500 liters capacity
Power Consumption	1000-2500 watts	100-400 watts
Energy Efficiency	ISEER/Star Rating 3-5	BEE Star Rating 3-5
Refrigerant Type	R32, R410A	R600a, R134a
Voltage/Frequency	220-240V/50Hz	220-240V/50Hz

Mnemonic: "CPERS" - Capacity, Power, Efficiency, Refrigerant, Supply specifications

Question 3(b OR) [4 marks]

Explain electronic controller for washing machine.

Answer:

Electronic Controller for Washing Machine:

flowchart TD
    A[User Interface] --> B[Microcontroller]
    B --> C[Motor Driver]
    B --> D[Water Valve Control]
    B --> E[Temperature Sensor]
    B --> F[Water Level Sensor]
    B --> G[Door Lock Control]
    B --> H[Drain Pump Control]

Microcontroller: Central processing unit that controls all operations
Sensors: Water level, temperature, load balance, door position
Actuators: Motor driver, water valves, heater, drain pump
User Interface: Program selection, temperature, spin speed settings

Mnemonic: "MIST-WAD" - Microcontroller Integrates Sensors and Timers for Water, Agitation and Drainage

Question 3(c OR) [7 marks]

Draw and explain block diagram of Microwave oven. List wiring and safety instructions for microwave oven

Answer:

Microwave Oven Block Diagram:

flowchart LR
    A[Control Panel] --> B[Control Circuit]
    B --> C[High Voltage Transformer]
    C --> D[High Voltage Capacitor]
    D --> E[Magnetron]
    E --> F[Waveguide]
    F --> G[Cooking Cavity]
    B --> H[Turntable Motor]
    B --> I[Fan Motor]
    B --> J[Door Interlock Switches]

Control Circuit: Processes user inputs and controls timing
High Voltage Transformer: Steps up voltage to 2000-4000V
Magnetron: Generates microwave radiation at 2.45 GHz
Waveguide: Directs microwaves into cooking cavity
Turntable: Ensures even cooking through rotation

Safety Instructions:

Never operate with door open or damaged
Ensure proper grounding
Don't override safety interlocks
Use microwave-safe containers only

Wiring Instructions:

Use appropriate gauge power cable (typically 14-16 AWG)
Connect to dedicated 15-20A circuit
Ensure proper ground connection
Keep wiring away from heat sources

Mnemonic: "MAGIC" - Magnetron And Guided waves Into Cavity

Question 4(a) [3 marks]

Draw block diagram of Photocopier.

Answer:

Photocopier Block Diagram:

flowchart LR
    A[Document Scanner] --> B[Image Processor]
    B --> C[Laser Unit]
    C --> D[Photosensitive Drum]
    E[Charging Unit] --> D
    D --> F[Developer Unit]
    F --> G[Transfer Unit]
    G --> H[Paper Feed]
    G --> I[Fusing Unit]
    I --> J[Output Tray]

Scanner: Captures original document image
Drum: Holds electrostatic image
Developer: Applies toner to charged areas
Transfer: Transfers toner to paper
Fuser: Melts toner permanently onto paper

Mnemonic: "SDTFO" - Scan, Develop, Transfer, Fuse, Output

Question 4(b) [4 marks]

List specifications of MF printer and CCTV.

Answer:

Specifications:

MF Printer Specifications	CCTV Specifications
Print Resolution: 600-1200 dpi	Camera Resolution: 2-8 MP
Print Speed: 15-40 ppm	Frame Rate: 15-30 fps
Scan Resolution: 300-600 dpi	Storage: 1-8 TB HDD/NVR
Paper Capacity: 150-500 sheets	Night Vision: 10-30m range
Connectivity: USB, Ethernet, Wi-Fi	Connectivity: Coaxial/IP/Wireless
Functions: Print, Scan, Copy, Fax	Video Format: H.264/H.265

Mnemonic: "RSCPF" - Resolution, Speed, Capacity, Protocol, Function specifications

Question 4(c) [7 marks]

Explain working of laser printer with block diagram.

Answer:

Laser Printer Working:

flowchart LR
    A[Data Processing] --> B[Laser Unit]
    B --> C[Photosensitive Drum]
    D[Primary Corona] --> C
    C --> E[Developer Unit]
    E --> F[Transfer Corona]
    F --> G[Paper Transport]
    G --> H[Fusing Unit]
    H --> I[Output]
    J[Cleaning Unit] --> C

Working Process:

Charging: Corona wire gives drum uniform negative charge
Writing: Laser neutralizes charges on drum to form image
Developing: Toner adheres to discharged areas of drum
Transfer: Paper receives positive charge, attracts toner
Fusing: Heat and pressure melt toner onto paper
Cleaning: Residual toner is removed from drum

Resolution: Determined by laser precision (600-1200 dpi)
Speed: Based on drum rotation and paper transport (15-40 ppm)

Mnemonic: "CWTFC" - Charge, Write, Transfer, Fuse, Clean cycle

Question 4(a OR) [3 marks]

Draw block diagram of CCTV.

Answer:

CCTV System Block Diagram:

flowchart LR
    A[Cameras] --> B[Video Transmission]
    B --> C[Digital Video Recorder]
    C --> D[Storage HDD]
    C --> E[Monitor Display]
    F[Power Supply] --> A
    F --> C
    G[Network Switch] --> C
    C --> H[Remote Access]

Cameras: Capture video footage
Transmission: Coaxial cable/IP network/Wireless
DVR/NVR: Processes and records video
Storage: Hard drives for footage retention
Monitor: Displays live or recorded footage

Mnemonic: "CTDSM" - Camera, Transmission, DVR, Storage, Monitor system

Question 4(b OR) [4 marks]

List specifications of inkjet printer and Photocopier.

Answer:

Specifications:

Inkjet Printer Specifications	Photocopier Specifications
Print Resolution: 1200-4800 dpi	Copy Resolution: 600-1200 dpi
Print Speed: 8-20 ppm	Copy Speed: 20-60 cpm
Ink Type: Dye/Pigment	Toner Type: Dry/Liquid
Paper Capacity: 100-250 sheets	Paper Capacity: 250-2000 sheets
Connectivity: USB, Wi-Fi	Functions: Copy, Scan, Print, Fax
Duty Cycle: 1,000-5,000 pages/month	Duty Cycle: 10,000-100,000 pages/month

Mnemonic: "RSIPCD" - Resolution, Speed, Ink/toner, Paper capacity, Connectivity, Duty cycle

Question 4(c OR) [7 marks]

Explain working of LCD projector with block diagram and list its specifications.

Answer:

LCD Projector Working:

flowchart LR
    A[Input Source] --> B[Signal Processor]
    B --> C[Lamp/Light Source]
    C --> D[Condenser Lens]
    D --> E[Dichroic Mirrors]
    E -->|Red| F[Red LCD Panel]
    E -->|Green| G[Green LCD Panel]
    E -->|Blue| H[Blue LCD Panel]
    F --> I[Prism]
    G --> I
    H --> I
    I --> J[Projection Lens]
    J --> K[Screen]

Working Process:

Light Generation: High-intensity lamp produces white light
Color Separation: Dichroic mirrors split light into RGB
Modulation: LCD panels control light intensity for each color
Recombination: Prism reassembles RGB images
Projection: Lens system projects image onto screen

Specifications:

Resolution: XGA (1024×768), WXGA (1280×800), FHD (1920×1080)
Brightness: 2000-5000 ANSI lumens
Contrast Ratio: 2000:1 to 20000:1
Lamp Life: 3000-6000 hours
Throw Ratio: 0.5:1 to 2.0:1
Connectivity: HDMI, VGA, USB, Wi-Fi

Mnemonic: "LSPMPS" - Lamp, Split, Panels, Modulate, Prism, Screen

Question 5(a) [3 marks]

Draw block diagram of PA system.

Answer:

Public Address (PA) System Block Diagram:

flowchart LR
    A[Microphone] --> B[Pre-amplifier]
    B --> C[Mixer]
    D[Audio Source] --> C
    C --> E[Equalizer]
    E --> F[Power Amplifier]
    F --> G[Speaker Network]
    H[Volume Control] --> C

Microphone: Converts sound to electrical signals
Pre-amplifier: Boosts microphone signal
Mixer: Combines multiple audio sources
Equalizer: Adjusts frequency response
Power Amplifier: Increases signal power
Speakers: Convert electrical signals back to sound

Mnemonic: "MMEPS" - Microphone, Mixer, Equalizer, Power amp, Speakers

Question 5(b) [4 marks]

Explain tweeter and woofer.

Answer:

Speaker Components:

Feature	Tweeter	Woofer
Frequency Range	High (2kHz-20kHz)	Low (20Hz-2kHz)
Size	Small (0.5"-1.5")	Large (4"-15")
Diaphragm	Light, rigid (dome/cone)	Heavy, flexible cone
Voice Coil	Small diameter	Large diameter
Cabinet Design	Horn/sealed	Ported/sealed/bass reflex

Working Principle:

flowchart LR
    A[Audio Signal] --> B[Crossover Network]
    B -->|High Frequencies| C[Tweeter]
    B -->|Low Frequencies| D[Woofer]
    C --> E[High-Frequency Sound Waves]
    D --> F[Low-Frequency Sound Waves]

Tweeter: Reproduces high frequencies with clarity and detail
Woofer: Reproduces low frequencies with power and depth

Mnemonic: "THSL" - Tweeters handle Highs, Small and Light; Woofers handle Lows

Question 5(c) [7 marks]

Define microphone. List types of microphone and explain working of any one type of microphone.

Answer:

Microphone Definition: A microphone is an electroacoustic transducer that converts sound waves into electrical signals.

Types of Microphones:

Type	Working Principle	Applications
Dynamic	Electromagnetic induction	Live performance, broadcasting
Condenser	Electrostatic principles	Studio recording, smartphones
Ribbon	Electromagnetic induction	Studio vocals, instruments
Carbon	Resistance variation	Old telephones
Piezoelectric	Piezoelectric effect	Contact mics, instruments
MEMS	Micro-electromechanical	Laptops, tiny devices

Dynamic Microphone Working:

flowchart LR
    A[Sound Waves] --> B[Diaphragm]
    B --> C[Attached Coil]
    C --> D[Movement in Magnetic Field]
    D --> E[Induced Voltage]
    E --> F[Electrical Signal Output]

Sound Capture: Diaphragm vibrates with sound waves
Transduction: Coil attached to diaphragm moves within magnetic field
Signal Generation: Movement induces voltage proportional to sound intensity
Output: Low impedance, strong signal requiring minimal amplification
Advantages: Durable, handles high SPL, no external power needed

Mnemonic: "DDCMIO" - Diaphragm Displaces Coil in Magnetic field Inducing Output

Question 5(a OR) [3 marks]

Define: (1) Pitch (2) Loudspeaker (3) Reverberation.

Answer:

Definitions:

Term	Definition
Pitch	The perceived frequency of a sound that determines how "high" or "low" it sounds
Loudspeaker	An electroacoustic transducer that converts electrical signals into sound waves
Reverberation	The persistence of sound after the original sound has stopped due to multiple reflections

Diagram:

Reverberation
    |
    v
Original Sound -----> Early Reflections -----> Late Reflections
    ^                       |                       |
    |                       v                       v
Direct Sound           Clarity (≤80ms)       Spaciousness (>80ms)

Mnemonic: "PLR Sound" - Pitch defines tone, Loudspeaker produces it, Reverberation extends it

Question 5(b OR) [4 marks]

Draw block diagram of Home theatre sound system and explain in brief.

Answer:

Home Theatre Sound System:

flowchart TD
    A[Audio/Video Source] --> B[AV Receiver/Amplifier]
    B --> C[Front Speakers]
    B --> D[Center Speaker]
    B --> E[Surround Speakers]
    B --> F[Subwoofer]
    B --> G[Video Display]
    H[Remote Control] --> B

AV Receiver: Central hub that processes audio/video signals
Front Speakers: Left and right channels for stereo sound
Center Speaker: Delivers dialog and central sounds
Surround Speakers: Create immersive environment with ambient sounds
Subwoofer: Reproduces low-frequency effects (LFE) below 120Hz
Configuration: Common setups include 2.1, 5.1, 7.1, or 9.1 channel systems

Mnemonic: "AFSCS" - Amplifier drives Front, Surround, Center Speakers and Subwoofer

Question 5(c OR) [7 marks]

Explain Electrostatic loudspeaker and permanent magnet loudspeaker.

Answer:

Comparison of Loudspeaker Types:

Feature	Electrostatic Speaker	Permanent Magnet Speaker
Working Principle	Electrostatic forces between plates	Electromagnetic induction
Construction	Thin diaphragm between stator plates	Cone attached to voice coil in magnetic field
Power Requirements	Needs high voltage polarizing supply	No external power beyond signal
Frequency Response	Excellent mid/high frequency	Good across full range with proper design
Efficiency	Low (1-3%)	Moderate (2-5%)
Distortion	Very low	Moderate

Electrostatic Speaker Working:

flowchart LR
    A[Audio Signal] --> B[Step-up Transformer]
    C[High Voltage DC Supply] --> D[Charged Diaphragm]
    B --> E[Conductive Stator Plates]
    E --> F[Electrostatic Force]
    F --> D
    D --> G[Sound Waves]

Diaphragm: Thin, lightweight membrane with conductive coating
Operation: Audio signal varies charge on stator plates, creating varying force on diaphragm

Permanent Magnet Speaker Working:

flowchart LR
    A[Audio Signal] --> B[Voice Coil]
    C[Permanent Magnet] --> D[Magnetic Field]
    B --> E[Current in Coil]
    E[Current in Coil] --> F[Electromagnetic Force]
    F --> G[Cone Displacement]
    G --> H[Air Movement]
    H --> I[Sound Waves]

Voice Coil: Winding of wire attached to speaker cone
Operation: Current through coil creates magnetic field that interacts with permanent magnet
Advantages: Robust design, good power handling, no high voltage required
Applications: Most common speaker design for general audio reproduction

Mnemonic: "ESPM" - Electrostatic uses Static charges, Permanent Magnet uses Magnetic forces