3.1 Repair/Replacement of Faulty Components

When equipment fails, the technician has two choices: repair the faulty part or replace it. A repair restores the original part, for example by resoldering a cracked joint or tightening a loose terminal. A replacement removes the part and fits a new one of the same specification. The choice depends on what failed, the cost of the part and the time needed, the availability of a spare, and whether the repair will be reliable. A cracked solder joint is repaired, a burnt resistor or a swollen capacitor is replaced, and a module that is sealed or costs less than the labour to open it is replaced as a whole.

Every job follows the same sequence: switch off and isolate the equipment, discharge stored energy, inspect, locate the fault, repair or replace, test, reassemble and record. This topic covers the maintenance activities involved and the safe disposal of the waste they create.

3.1.1 Maintenance activities

Maintenance activities are the practical actions that keep equipment working or bring it back into service. Before any of them, disconnect the equipment from the supply, wait for large capacitors to discharge (in a power supply or a television this can take minutes) and, where necessary, discharge them with a suitable resistor. Wear anti-static protection when handling circuit boards, and keep the workshop bench clear.

The activities fall into four groups: cleaning, tightening, soldering and assembling.

3.1.1.1 Cleaning

Dust, grease, flux and corrosion cause overheating, leakage between tracks and poor contacts, so cleaning is the first step of most repairs and is part of routine preventive maintenance.

Materials. A soft brush and a blower remove loose dust. Isopropyl alcohol (IPA) and a lint-free cloth or cotton bud remove flux residue and grease from boards. Contact cleaner restores connectors, switches and sockets. A fine eraser or a glass-fibre pen cleans oxidised contacts and pads.

Method.

1. Switch off, unplug and discharge the equipment.
2. Blow or brush the dust away, working from the top downward and keeping the dust moving out of the equipment.
3. Clean boards and connectors with a small quantity of cleaner, and do not soak them.
4. Allow all parts to dry fully before power is applied.

Cautions. Do not use tap water or household detergents on a circuit board, and never spray a liquid into equipment that is connected to the supply. Keep the brush from bending the legs of small parts. Use anti-static brushes and a wrist strap where the equipment contains sensitive devices.

3.1.1.2 Tightening

Vibration, heat cycling and ageing loosen screws, terminals and connectors. A loose connection has a higher resistance than a good one, and the extra resistance turns current into heat.

Example 1: A power terminal that should have a resistance of almost zero has loosened and now has a contact resistance of 0.05 Ω. The load draws 16 A. Find the power wasted as heat at the terminal.

P = I² R = 16² × 0.05 = 256 × 0.05 = 12.8 W

Answer: The loose joint dissipates 12.8 W in a very small place, which is enough to scorch insulation and char the terminal block. Retightening it removes the fault.

Method.

1. Check each screw, terminal and connector for looseness, signs of heating (darkened or melted insulation) and stripped threads.
2. Use the correct screwdriver or spanner, so that the head is not damaged.
3. Tighten firmly but not excessively. Over-tightening strips threads, cracks plastic casings and cuts through the strands of a conductor. Where the maker gives a torque, use a torque screwdriver.
4. Replace damaged screws and terminals instead of re-using them.
5. After tightening, pull gently on each conductor to prove that it holds.

Torque is the turning effect of a force, equal to the force multiplied by the distance from the axis. For example, a force of 20 N applied on a 0.12 m handle gives 20 × 0.12 = 2.4 N·m. A torque tool applies a set value, so every screw is tightened equally.

3.1.1.3 Soldering

Soldering joins a component lead to a pad on the circuit board with a molten alloy, called solder, which then solidifies to form a strong, electrically good joint. It is used to fit replacement parts and to repair cracked or dry joints.

Materials. A temperature-controlled soldering iron with a clean, tinned tip, solder with a flux core, a damp sponge or brass wool for tip cleaning, a desoldering pump or braid, a heat-proof stand and tweezers. Lead-free solder (a tin-based alloy) is preferred because it avoids lead, and leaded solder needs a lower temperature. Typical iron settings are about 320 °C to 350 °C for leaded solder and 350 °C to 380 °C for lead-free solder, but follow the maker's guidance.

Method.

1. Clean the pad and the component lead.
2. Place the component and hold it firmly.
3. Touch the iron to the pad and the lead together, so that both heat.
4. Feed solder to the joint, not to the iron tip, and let it flow around the lead.
5. Remove the solder, then the iron, and keep the joint still until it sets.
6. Inspect the joint: a good joint is smooth, shiny and has a concave fillet that wets both lead and pad.
7. Trim the lead if necessary.

Faults. A dry (cold) joint is dull, grainy or lumpy and has poor contact. A bridge links two neighbouring pads and shorts them. Too much heat lifts the track from the board.

Desoldering. To remove a part, heat the joint and use the pump to suck the solder away or the braid to draw it off, then lift the lead out. Do not force a component out, because that can tear the track.

3.1.1.4 Assembling

After a repair, the equipment is reassembled in the reverse order of disassembly. Careful assembly prevents new faults.

1. Check that the repair is finished and that the work area is free of loose screws, wire strands and solder droplets, which can short circuits.
2. Place the boards and modules in their correct positions and plug in connectors fully, observing the polarity and the keying.
3. Route cables as they were and secure them with ties or clips, away from heat, moving parts and sharp edges.
4. Replace the earth connections and shields, since leaving out an earth lead makes the equipment unsafe.
5. Fit the screws in the right holes. A long screw in a short hole can touch a component.
6. Test the equipment before closing the case, then close and test it again.
7. Record what was replaced and the parts used.

A good habit is to photograph the equipment before disassembly or to keep screws and parts sorted in a labelled tray, so that nothing is lost or mixed.

3.1.2 Disposal of waste materials

Repair work creates waste: old batteries, scrap metal and plastics, and failed boards. Some of it is hazardous. Lead, brominated flame retardants and the chemicals in batteries pollute soil and water, and burning plastics produces poisonous fumes. Waste is therefore sorted at the bench into separate labelled containers, and nothing is burned or thrown into ordinary rubbish.

Electronic waste in Kenya is handled under the National Environment Management Authority (NEMA) rules. In practice, hazardous waste is stored safely and handed only to a handler or recycler licensed by NEMA, and a record of what was handed over is kept. The Environmental Management and Co-ordination (Waste Management) Regulations, 2006 and the Sustainable Waste Management Act, 2022 govern the collection, transport and disposal of waste.

3.1.2.1 Old batteries

Batteries include lead-acid, nickel-metal hydride, alkaline and lithium-ion types. All contain materials that harm the environment, and some can burn. A swollen, hot or leaking battery is a hazard and must be handled carefully with gloves and eye protection.

Method. Remove batteries from the equipment, tape over the terminals of lithium and other cells to prevent short circuits, and store them by type in a dry, non-conductive container away from heat. Never puncture, crush or burn a battery. Never mix leaking batteries with others. Hand them to a recycler or collection point.

3.1.2.2 Lugs and screws

Cable lugs, terminals, screws, nuts and washers are small metal parts of steel, brass or copper. They are collected in a container, sorted by metal if the volume justifies it, and sold or given to a metal recycler. Do not mix them with the general rubbish, and keep sharp parts from injuring the hand when sorting.

3.1.2.3 Tapes

Insulating tape is made of PVC or similar plastic with an adhesive, and it cannot be recycled with the metals. Used tape and its backing are collected and disposed of with general waste in sealed bags. Burning tape produces smoke that irritates the lungs. Reduce waste by cutting only the length needed.

3.1.2.4 Cable sheaths

Cable sheaths are made of PVC or similar plastic and cover copper or aluminium conductors. Strip the sheath and insulation from the conductor, collect the metal for recycling and collect the plastic for a plastic recycler or general waste. Burning cables to recover copper is dangerous and against the waste rules, since it produces toxic fumes and pollutes the air.

3.1.2.5 PCBs

Here PCBs means printed circuit boards: the green boards that carry the components. They contain copper, solder (often with lead), flame retardants and sometimes precious metals, so they have value for recyclers and are hazardous if dumped. Keep them in a labelled container and send them to a licensed e-waste recycler. Do not burn them or soak them in acid to recover metals, because both are harmful. Old oil-filled capacitors and transformers may contain a different substance, also abbreviated PCBs (polychlorinated biphenyls). These are toxic, and the equipment must be handed to a specialist.

3.1.2.6 Off cuts

Off cuts are the small pieces left over from the work: wire ends, trimmed component leads, cut cable and solder droplets. They are sharp and can pierce skin or get into eyes. Collect them with the bench tray or a catch container while cutting, sweep rather than blow them, and recycle the copper and the leaded solder with the metals.

Record what was disposed of, the quantity and who received it. These records are needed to show that waste was handled correctly.

Chapter Summary

This chapter focused on the essential maintenance activities involved in the repair and replacement of faulty electrical and electronic components. Key procedures such as cleaning, tightening, soldering, and assembling were discussed in detail to ensure effective servicing and prolong equipment lifespan. Proper disposal of waste materials, including old batteries, lugs and screws, tapes, cable sheaths, printed circuit boards, and off cuts, was emphasized to promote environmental safety and compliance. The chapter also covered the importance of adhering to Environmental Health and Safety (EHS) regulations to protect both technicians and users during maintenance work. Additionally, Occupational Safety and Health Administration (OSHA) regulations were examined, highlighting the legal requirements and safety practices necessary for maintaining a safe working environment. Together, these topics provide a comprehensive framework for performing maintenance activities responsibly and efficiently in electrical and electronic equipment repair.