Electronics and Device Repair

A circuit is a closed loop that lets current flow. Voltage pushes the current, and resistance limits it. Knowing the link between them lets you predict what should happen.

• Voltage is the push, measured in volts, current is the flow, measured in amps, and resistance is the opposition, measured in ohms.
• The basic rule is that voltage equals current times resistance, written V = I x R, so current equals voltage divided by resistance.
• In a series circuit the parts share one path and resistances add, while in a parallel circuit each part has its own path.
• Power in watts equals volts times amps, which tells you how hot a part may get.
• Work only with safe low voltage, and never practise on mains-powered equipment.

Activity. Solve at least six circuit problems on paper, including two series and one parallel, and show the working and units for each.

Standard to meet. Answer at least five of your six correctly with units, and explain how the series and parallel results differ.

Safe habits protect you and the device. You unplug, discharge stored energy and protect parts from static. A supervisor signs off before you start.

• Never open or repair a mains-powered device, and check with your local authority and your supervisor for the rules that apply.
• Disconnect the power and remove any battery before you open a device, and wait for stored charge to fall.
• Wear an anti-static wrist strap and work on a mat so static, also called electrostatic discharge or ESD, does not damage sensitive parts.
• Keep your bench tidy, wear eye protection when you solder or cut and keep long hair and loose clothes away.
• A common mistake is to assume a device is dead because it is switched off.

Activity. Write and sign a bench safety plan listing at least ten rules, then have your supervisor check and sign it.

Standard to meet. List at least ten rules in your plan, cover power, static, heat and eye protection, and obtain your supervisor's signature.

A multimeter measures voltage, resistance and continuity. Using it correctly gives you facts about the fault. You record every reading with its unit.

• Set the dial to the right mode and range before you touch the probes to the circuit.
• Measure voltage with the probes across a part and resistance only with the power off.
• Use continuity mode to test whether a wire, fuse or track conducts, because it beeps when it does.
• Compare each reading with the expected value and the tolerance and note whether it is inside the range.
• A common mistake is to measure resistance in a live circuit, which gives false readings and can damage the meter.

Activity. Measure at least eight parts, including resistors, a fuse and a cable, and complete a table of expected value, tolerance range, reading and verdict.

Standard to meet. List the unit for every reading in your table, calculate the tolerance ranges correctly and match your verdicts to the numbers.

Diagnosis moves from symptom to cause in a logical order. You ask questions, check the simple things and isolate the fault step by step. Writing it down prevents going in circles.

• Ask the user what happened, when it started and what was done before the fault appeared.
• Look first at the obvious things such as the power lead, the fuse, the connectors and the battery.
• Measure the voltage at the input and then at each stage, to find where it stops.
• Change one thing at a time and retest, so you know which change fixed the fault.
• A common mistake is to replace several parts at once, which hides the real cause and wastes parts.

Activity. Diagnose five faulty low-voltage devices and write a record for each with symptom, steps, readings and the confirmed cause.

Standard to meet. Show in each record at least three measured readings, one change at a time and a cause backed by a measurement.

Good soldering makes a clean, strong joint. You heat, feed solder and inspect. After each repair you retest to make sure the fault is gone.

• Set the iron to a suitable temperature, often about 350 degrees C for common solder, and keep the tip clean and tinned.
• Heat the part and the pad together for two to three seconds, then touch the solder to the joint and not to the iron.
• Remove the solder first and then the iron, and let the joint cool without moving it.
• Inspect each joint with a magnifier for a shiny, smooth, cone-shaped finish, and redo any dull or lumpy joint.
• Use extraction or fume control at the bench and keep the area ventilated.

Activity. Complete at least five repairs, each with a photo of the joint, a retest reading and a note of any rework.

Standard to meet. Pass at least 90% of final joints at inspection and record a before and after reading for every repair.

A repair is not finished until you have proved it works. Tests and records protect you and the customer. A soak test shows faults that appear after warm-up.

• Write a short test list for each type of device that covers power, function and any safety item.
• Run the device for a soak test, such as one hour, and check it at the start, the middle and the end.
• Record the readings and the result of each test with the date and your initials.
• Keep a return record so repeat faults can be compared.
• A common mistake is to hand a device back after a one-minute test.

Activity. Complete a test and record sheet for each of your five repairs, with the soak test results and sign-off.

Standard to meet. Record all five repairs in full, record the soak test result and follow up any failures.

Each repair has a cost made of parts, time and risk. You work it out so you can price fairly. A warranty is part of the price.

• List the parts used with their cost and the time spent on the repair.
• Value your time at a stated hourly rate and include a small amount for tools and consumables.
• Add the cost of parts and time to get the cost per repair, and add a margin to set the price.
• Decide the warranty period and the cost you set aside for rework.
• A common mistake is to leave out your time or the cost of a repeat repair.

Activity. Complete a cost sheet for all five repairs with parts, time, total cost and proposed price.

Standard to meet. Check that your totals are correct, add a note to every cost and write down your warranty reasoning.

The review looks across all your repairs for patterns. Repeat faults point to a weakness in the design or the way devices are used. You write down what you would do differently.

• Group your five faults by type, such as cable break, blown fuse or bad joint.
• Count how often each type occurs and note which parts fail most.
• Suggest a prevention for the most common fault, such as strain relief on a cable.
• Review your safety record and note any near misses and how to avoid them.
• A common mistake is to review only the success stories.

Activity. Present a review with a faults table, one prevention idea and a plan for your next five repairs.

Standard to meet. Match your table totals to your records and link your prevention idea to the most common fault.