Practical: Replacing Computer Components – JSS3 Computer Hardware & GSM Repair Lesson Note (First Term)

Replacing computer components is the practical skill of removing a faulty part, such as the power supply unit or motherboard, and fitting a working one safely.

• Class: JSS 3
• Subject: Computer Hardware and GSM Repair
• Focus: Practical guide to Power Supply Unit (PSU) and motherboard replacement.

Behavioural objectives

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

1. State the functions of the power supply unit and the motherboard.
2. List three signs of a faulty PSU.
3. Explain why static electricity must be controlled when handling a motherboard.
4. Replace a PSU by following the steps in the correct order.
5. Replace a motherboard and connect the front panel headers correctly.

What tools and safety rules do you need?

You need a few simple tools and must follow basic safety rules before you open any computer.

• Screwdriver: removes the side panel and the screws that hold the parts.
• Phone camera: takes photos of the cable layout before you disconnect anything.
• Small container: keeps screws together so none is lost.
• Anti-static wrist strap: lets static electricity flow away from your body, if available.
• Power off: switch off and unplug the computer from the wall before opening the case.

What is a power supply unit (PSU)?

The power supply unit (PSU) is the metal box inside the computer that changes the strong mains electricity from the wall into the low-voltage electricity the parts can use.

• Position: the power cord from the wall plugs into the PSU at the back of the case.
• Input: high-voltage alternating current (AC) from the wall socket.
• Output: low-voltage direct current (DC) sent by cables to the motherboard, hard drive and fans.

What are the signs of a bad PSU?

A bad PSU usually shows one or more of three signs.

• No power: the computer does not turn on at all, with no lights and no fans.
• Burning smell: a smell like fried wire comes from the case.
• Sudden restarts: the computer restarts by itself while you are working.

Other faults can cause these signs too, so test the power cable and wall socket first.

How do you replace a PSU?

A PSU is replaced by unplugging it, unscrewing it from the case, and fitting a new one in the same place.

1. Safety first: unplug the main power cable from the wall.
2. Open the case: use a screwdriver to remove the side panel.
3. Unplug internal cables: gently disconnect all the colourful wires from the PSU that go to the motherboard, the hard drive and the fans.
4. Unscrew the box: remove the 4 screws at the back of the case. Hold the PSU with one hand so it does not fall.
5. Slide it out: lift the old PSU out and slide the new one into the same space.
6. Screw it in: fix the new PSU with the 4 screws at the back.
7. Reconnect the cables: plug the cables back into the motherboard, hard drive and fans.
8. Test: close the case, plug in the power and switch on.

• Tip: choose a replacement PSU with the same type of fitting and enough power for the computer.

What is a motherboard?

The motherboard is the largest circuit board in the computer, and every other part sits on it or connects to it.

• Copper paths: thin copper lines on the board carry signals between parts, like nerves in the body.
• Care: one deep scratch can cut a copper path, so replacing a motherboard needs great care.

Why is static electricity dangerous to a motherboard?

Static electricity is an electric charge that can build up on your body and damage delicate chips when you touch them.

• Simple trick: touch the metal frame of the computer case often while you work.
• Why it works: the charge passes into the metal instead of into the chips.
• Better method: wear an anti-static wrist strap clipped to the metal case.
• Handling: hold the board by its edges and keep it away from carpet or plastic bags.

How do you prepare to replace a motherboard?

Preparation means recording where everything connects and removing parts that make the board heavy or hard to handle.

• Take a photo: photograph the old motherboard with a phone before you disconnect anything, to remember where the wires go.
• Remove the RAM: pull the RAM out of its slots.
• Remove the CPU fan: this makes the board lighter and easier to lift.

What are the steps to replace a motherboard?

A motherboard is replaced by removing all connections, unscrewing the old board, and screwing the new board onto the case standoffs.

1. Disconnect everything: remove all cables, the graphics card and the RAM.
2. Unscrew the board: remove the 6 to 9 small screws. They go into standoffs, the little brass legs that keep the board from touching the metal case.
3. Change the I/O shield: pop out the silver rectangular plate at the back where the USB ports show. Snap in the new one that came with the new board.
4. Line it up: lay the new board down gently. The holes must line up exactly with the brass standoffs.
5. Screw it down: turn each screw until it is firm. Do not over-tighten, because the board can crack.

What do these motherboard terms mean?

These five terms are the main words used in this practical.

How do you connect the front panel headers?

Front panel headers are the tiny wires that connect the buttons and lights on the front of the case to the motherboard.

Look for small labels printed on the board:

• PWR_SW: the power switch.
• RESET_SW: the reset switch.
• HDD_LED: the hard drive light.

• Risk: if the power switch wire is wrong, the power button will not work.
• Check: always read the motherboard manual or the tiny labels on the board.

How do you test the computer after replacing the motherboard?

The final test is to reconnect power, switch on, and check that the fans spin and the screen shows a display.

1. Reconnect the big 24-pin power cable from the PSU to the motherboard.
2. Reconnect the 4-pin or 8-pin CPU power cable.
3. Plug in the monitor and the power cable.
4. Press the power button. If the fans spin and writing appears on the screen, the rebuild is successful.

What if the fans spin but the screen is blank?

• Monitor cable: check that it is firmly plugged into the computer and the monitor.
• RAM: remove it and push it firmly back into its slots.
• Graphics card: check that it sits fully in its slot and that the monitor cable is in the right port.

Evaluation

1. Why is it important to touch the metal case before touching the motherboard?
2. What is the job of the I/O shield (the silver plate)?
3. If the computer fans are spinning but nothing shows on the screen, which part would you check first?
4. What happens if you forget to fit the brass standoffs before putting in the motherboard?
5. List three signs of a bad PSU.

Assignment

Write the steps for replacing a PSU in your exercise book, in the correct order, and state one safety rule for each of the first two steps.