Safety Precaution in Television Workshop for SS 3

Class: SS 3
Term: First Term
Week: 1
Age: 16 years
Duration: 45 minutes
Subject: Radio, TV and Electronics
Curriculum Theme: Safety Precaution in Television Workshop
Previous Lesson:
Topic: SAFETY PRECAUTION IN TELEVISION WORKSHOP.
Subject Matter: Power supply; Picture tube; Extra-high voltage section; Components ratings

Specific Objectives

By the end of the lesson, pupils/students should be able to:

Cognitive Domain

• Identify potential danger points in a television set related to power supply, picture tube, and extra-high voltage section.
• Explain the safety precautions associated with different component ratings.
• State the appropriate procedures for handling high-voltage sections in a TV workshop.

Affective Domain

• Appreciate the importance of safety measures in a television workshop environment.
• Observe and follow safety guidelines when working with electronic equipment.
• Understand the risks involved in neglecting safety precautions.

Psychomotor Domain

• Demonstrate the safe dismantling of a TV set under supervision.
• Handle components with appropriate safety practices, especially those related to high voltage.

Reference Materials

The following resources were used in planning this lesson:

• 2025 Revised 9 Years Basic Education Curriculum
• Relevant State Unified Scheme of Work
• Electronics Workshop Safety Manuals
• The HeadTeacher Scheme of work

Instructional Materials

The teacher will teach this lesson with the aid of:

• A working television set (for demonstration)
• Insulated tools (screwdrivers, pliers)
• Safety gloves and goggles
• Multimeter
• Circuit diagrams of a TV set
• Warning signs and labels

Rationale for the Lesson

This lesson is essential for students to develop a strong safety consciousness before engaging in practical work with electronic devices. Understanding safety precautions prevents accidents, protects equipment, and ensures a secure learning environment. It equips students with the foundational knowledge to handle complex electronic systems responsibly.

Prerequisite/Previous Knowledge

Students should have basic knowledge of electricity, simple electronic components, and general workshop safety rules.

Lesson Content/Board Summary

SAFETY PRECAUTION IN TELEVISION WORKSHOP

Safety Precautions for Power Supply Section

The power supply section of a television set contains high voltage and can store dangerous charges even after being switched off. Proper precautions are crucial to avoid electric shock.

1. Always unplug the television from the mains power supply before attempting any work.
2. Wait for several minutes after unplugging to allow filter capacitors to discharge.
3. Use a discharge tool or a resistor with insulated leads to safely discharge large electrolytic capacitors in the power supply section.
4. Never work on a live circuit unless absolutely necessary for troubleshooting, and always use insulated tools and a spotter.
5. Check the fuse rating and replace it only with a fuse of the correct specified rating.

Safety Precautions for Picture Tube (CRT)

The Cathode Ray Tube (CRT) in older television sets is a vacuum tube that can implode if mishandled, and it also holds a high voltage charge.

1. Handle the picture tube with extreme care to prevent breakage or implosion.
2. Wear safety goggles and thick gloves when working near the CRT.
3. Avoid striking or dropping the CRT.
4. Discharge the anode cap (extra-high voltage terminal) of the picture tube using a high-voltage probe before touching it.
5. Do not attempt to remove the picture tube without proper training and tools.

Safety Precautions for Extra-High Voltage (EHT) Section

The Extra-High Voltage (EHT) section generates very high voltages (thousands of volts) for the picture tube, posing a severe electrocution risk.

1. Always ensure the television is unplugged and discharged before working on the EHT section.
2. Use only properly insulated tools when working on or near the EHT section.
3. Never touch the EHT anode cap or flyback transformer output directly without discharging it first.
4. Be aware that the EHT capacitor can retain a charge for a long time.
5. Work with one hand behind your back to prevent a complete circuit through your body in case of accidental contact.

Safety Precautions for Component Ratings

Using components with incorrect ratings can lead to overheating, component failure, fire, or electric shock.

1. Always replace components with parts that have the same or equivalent specifications (voltage, current, power, resistance, capacitance, etc.).
2. Never use components with lower voltage or current ratings than specified in the circuit design.
3. Ensure power resistors are adequately rated for the power they dissipate to prevent overheating.
4. Check the temperature ratings of components, especially in high-power sections.
5. Refer to the television’s service manual for correct component specifications.

Teaching Methods/Instructional Techniques

Discussion, Demonstration, Guided Practice, Question and Answer, Explanation, Observation, Practical Activity.

Instructional Procedures

Step 1: Introduction

Time: 5 minutes

Teaching Skill: Questioning/Activating Prior Knowledge

Teacher’s Activity: The teacher greets the students and asks them about general safety rules they know for working with electrical appliances or in a workshop. The teacher then introduces the topic: Safety Precautions in a Television Workshop, emphasizing its importance.

Pupils’ Activity: Students respond to questions about general safety and listen attentively to the introduction.

Learning Point: Workshop safety importance

Step 2: Exploring Power Supply Safety

Time: 8 minutes

Teaching Skill: Demonstration/Explanation

Teacher’s Activity: The teacher displays a TV set and identifies the power supply section. He explains the dangers associated with it, such as high voltage and stored charges in capacitors. He demonstrates how to safely unplug and discharge capacitors using appropriate tools.

Pupils’ Activity: Students observe the demonstration and ask questions for clarification.

Learning Point: Power supply hazards

Step 3: Understanding Picture Tube Safety

Time: 7 minutes

Teaching Skill: Explanation/Visual Aid

Teacher’s Activity: The teacher points out the picture tube (CRT) on the TV set. He explains the risks of implosion and the high voltage present at the anode cap. He instructs on the use of safety goggles and gloves and how to discharge the anode cap.

Pupils’ Activity: Students listen, observe the CRT, and note the safety gear and discharge procedure.

Learning Point: Picture tube dangers

Step 4: Addressing Extra-High Voltage (EHT) Section Safety

Time: 7 minutes

Teaching Skill: Demonstration/Guidance

Teacher’s Activity: The teacher identifies the EHT section and flyback transformer. He explains the extremely high voltages involved and demonstrates how to use insulated tools and the “one-hand” rule when working near this section. He stresses the importance of ensuring the TV is fully discharged.

Pupils’ Activity: Students observe the EHT section and the safety demonstration, understanding the high risks.

Learning Point: Extra-high voltage risks

Step 5: Component Ratings and Safety

Time: 6 minutes

Teaching Skill: Explanation/Discussion

Teacher’s Activity: The teacher explains the concept of component ratings (voltage, current, power) and why it is crucial to replace components with those of correct specifications. He shows examples of components with their ratings.

Pupils’ Activity: Students listen, examine component examples, and discuss the implications of incorrect ratings.

Learning Point: Component rating safety

Step 6: Guided Practical Observation

Time: 4 minutes

Teaching Skill: Guided Practice/Observation

Teacher’s Activity: The teacher, with adequate guidelines, instructs students to observe him as he carefully begins to dismantle a small part of the TV set, pointing out the identified danger points and demonstrating the appropriate handling practices for each.

Pupils’ Activity: Students follow the teacher’s guide to observe the dismantling process and the safe handling of danger points.

Learning Point: Safe TV handling

Step 7: Evaluation/Review

Time: 5 minutes

Teaching Skill: Questioning/Assessment

Teacher’s Activity: The teacher evaluates the learning by asking the following questions:

1. Mention two safety precautions for working with the power supply section of a TV.
2. Why is it dangerous to mishandle the picture tube?
3. What is the primary risk associated with the Extra-High Voltage (EHT) section?
4. Why must components be replaced with parts of the correct rating?

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Safety precaution knowledge

Step 8: Note-Taking

Time: 4 minutes

Teaching Skill: Guided Writing

Teacher’s Activity: The teacher guides pupils/students to copy the essential Board Summary notes on safety precautions in a television workshop into their notebooks.

Pupils’ Activity: Pupils/students copy the notes carefully into their notebooks.

Learning Point: Safety notes recording

Step 9: Conclusion

Time: 2 minutes

Teaching Skill: Reinforcement

Teacher’s Activity: The teacher summarises the key safety points discussed and reminds students that safety is paramount in any electronics workshop. He encourages them to always prioritize safety before starting any practical work.

Pupils’ Activity: Students listen and acknowledge the importance of safety.

Learning Point: Workshop safety reinforcement

Continuous Assessment/Further Study

Type: Homework/Further Reading

Instruction: Research and write short notes on the following:

1. The function of a discharge tool in an electronics workshop.
2. The specific dangers of working with capacitors in old TV sets.
3. How a multimeter can be used to check for residual voltage in a circuit.
4. List five general safety rules applicable to any electronics workshop.

Lesson Keywords

• Power supply – Section that converts AC mains to DC voltages for the TV.
• Picture tube (CRT) – Vacuum tube that displays images in older TVs.
• Extra-high voltage (EHT) – Very high voltage generated for the CRT anode.
• Component ratings – Electrical specifications (voltage, current, power) of electronic parts.
• Discharge tool – Device used to safely remove stored charge from capacitors.
• Anode cap – High-voltage terminal on the CRT.

Differentiation

For weaker learners, provide simplified diagrams of the TV sections and pre-label danger points. Allow them to work in pairs during observation. For faster learners, challenge them to research and present on advanced safety equipment or procedures, such as lockout/tagout systems for workshop machinery.

Suggested Lesson Videos

Search on YouTube for: “TV repair safety precautions” or “electronics workshop safety high voltage”

Teacher Guide for Using This Lesson Plan

Before the lesson, ensure the working TV set is safe for demonstration purposes and that all necessary insulated tools and safety gear (gloves, goggles, discharge tool) are available. Emphasize that students are to observe only and not touch components without explicit instruction and supervision. During the demonstration of dismantling, clearly articulate each step and the associated safety measure. Pay close attention to students’ understanding of the EHT section and capacitor discharge, as these are critical safety areas. Encourage questions throughout the lesson to clarify any misconceptions. Remind students that the Board Summary should be copied accurately into their notebooks during the note-taking step.