Chapter 1

Part A: Support and maintenance

Computer support and maintenance

Last updated November 20266 sectionsabout 9 min read

Key takeaways

Resistors limit current, capacitors store and release charge, diodes let current flow one way only and transistors amplify or switch signals; an integrated circuit puts a whole circuit on one chip.
Voltage is measured in volts, current in amperes and resistance in ohms, and Ohm's Law ties them together: V = I x R.
The wall socket supplies AC, but every internal component runs on DC, so the power supply unit converts one into the other.
Logic gates combine binary inputs into one output; NAND and NOR are universal, so any other gate can be built from them alone.
Preventive maintenance is scheduled work before a fault, corrective maintenance responds to one, and internal work starts only once the system is powered off, unplugged and the technician is protected against static.

Supporting and maintaining computer systems starts below the level of a whole machine: the electronic components that make up a circuit board, the physics that governs how they behave, and the digital logic those components are wired to implement. This chapter builds that foundation, then the tools, procedures and safety habits every support technician works by.

Electronic components

Resistor

Limits and controls the flow of current in a circuit; its value is measured in ohms (Ω).

Capacitor

Stores and releases electrical charge, used for filtering and smoothing power in a circuit.

Diode

Allows current to flow in one direction only, used for rectification (converting AC to DC).

Transistor

A semiconductor device that amplifies or switches electronic signals; millions of microscopic transistors etched onto silicon are what a modern CPU actually is.

Integrated circuit (IC)

A complete circuit, resistors, transistors and all, fabricated on a single small chip of semiconductor material, e.g. the CPU, RAM chips, and a motherboard's chipset.

Printed Circuit Board (PCB)

The rigid board (e.g. a motherboard) that physically holds components and connects them electrically through etched copper traces.

Physics of electronics

Three quantities describe how electricity behaves in any circuit a technician will work on: voltage (V, the electrical “pressure” pushing current, measured in volts), current (I, the rate of flow of charge, measured in amperes), and resistance (R, opposition to that flow, measured in ohms). Ohm's Law ties the three together, V = I × R, and is the basis for diagnosing why a component is drawing too much or too little power.

Direct Current (DC)

Current that flows in one constant direction; what every internal computer component (CPU, RAM, drives) actually runs on.

Alternating Current (AC)

Current that periodically reverses direction; what the wall socket supplies, converted to DC by the Power Supply Unit (PSU) before it reaches any internal component.

Semiconductor

A material (typically silicon) whose conductivity sits between a conductor and an insulator, and can be precisely controlled; the physical basis of diodes, transistors and every IC described under electronic components.

Digital logic

Underneath every instruction a computer executes is binary: two states, 0 and 1, represented electrically as low and high voltage. Logic gates are the transistor-built building blocks that combine binary inputs into a binary output, and every digital circuit in a computer, from a CPU's arithmetic unit to a memory chip's addressing, is ultimately built from them.

Gate	Output is 1 when…	Typical use
AND	all inputs are 1	Confirming multiple conditions must all hold at once.
OR	at least one input is 1	Confirming any one of several conditions holds.
NOT	its single input is 0 (inverts it)	Negating a signal.
NAND	not all inputs are 1 (AND, inverted)	A universal gate; any other gate can be built from NAND gates alone.
NOR	no input is 1 (OR, inverted)	Also universal, the other building-block gate.
XOR	inputs differ (exactly one is 1)	Detecting a difference between two bits, e.g. in binary addition.

Truth table: AND vs OR vs XOR (two inputs A, B)
A B | AND | OR | XOR
0 0 |  0  | 0  |  0
0 1 |  0  | 1  |  1
1 0 |  0  | 1  |  1
1 1 |  1  | 1  |  0

Maintenance tools and equipment

Screwdriver set

Phillips and flat-head, in the small sizes computer cases and expansion cards use; the single most-used tool for any hardware job.

Anti-static wrist strap

Clipped to an earthed point and worn on the wrist, it continuously discharges static electricity from the technician's body before it can damage a sensitive component (see Safety precautions, below).

Multimeter

Measures voltage, current and resistance; used to test whether a PSU, cable or component is delivering the power it should.

Compressed air / anti-static brush

Clears dust from fans, heatsinks and vents without touching (and risking scratching or discharging static onto) sensitive components.

Thermal paste

Fills microscopic gaps between a CPU and its heatsink so heat transfers efficiently; reapplied whenever a heatsink is removed.

Cable ties / management tools

Keep internal cabling tidy, improving airflow and making the next repair easier to work in.

Maintenance procedures

Preventive maintenance

Scheduled, routine work done before a fault occurs, dust removal, thermal paste renewal, cable inspection, software updates, to reduce the chance of failure.

Corrective maintenance

Work done in response to an actual fault, diagnosing and repairing or replacing whatever failed.

Documentation

Recording what was done, when, and by whom, on every maintenance visit; essential both for warranty/audit purposes and so the next technician does not repeat wasted diagnostic steps.

Follow the manufacturer's documented procedure for the specific model being serviced rather than a generic checklist alone
Power down and unplug the system before any internal work (see Safety precautions, below)
Work through a fault systematically rather than replacing parts by guesswork
Test the system fully after any maintenance before returning it to the user

Safety precautions

Electrostatic discharge (ESD)

A sudden, invisible static-electricity discharge that can permanently damage a component; prevented with the wrist strap, an anti-static mat, and touching a grounded metal surface before handling any component.

Power safety

Always power off and unplug a system, and discharge the PSU's residual capacitors, before opening the case; never work on live power.

Environmental safety

Keep liquids away from equipment, work in a dry, well-ventilated area, and never obstruct a system's ventilation once reassembled, overheating is itself a safety risk, not just a performance one (see the troubleshooting chapter).

Manual handling

Lift heavy equipment (towers, printers, monitors) with correct posture, and use two people or a trolley for anything awkward or heavy.

Fire safety

Never use water on an electrical fire; a CO₂ or dry-powder extinguisher rated for electrical equipment is the correct response.

Applying Ohm's Law

A resistor of 15 ohms has a current of 0.8 amperes flowing through it. Compute the voltage across it.

V = I x R = 0.8 x 15 = 12 volts.

A separate component has 10 volts across it and a resistance of 25 ohms. Compute the current flowing through it.

I = V / R = 10 / 25 = 0.4 amperes.

Exam tip

A recurring CISSE Foundation pattern pairs an electronic component with the physical quantity from the physics of electronics that describes it (“a resistor's value is measured in …”). Know the unit for each of voltage, current and resistance cold, and be ready to apply Ohm's Law (V = I × R) to a simple numeric question, not just define it.

Self-check

(a) A component has a resistance of 40 ohms and a current of 0.3 amperes flowing through it. Compute the voltage across it. (3 marks)

(b) Distinguish between AC and DC, and explain why a computer's internal components run on DC even though the wall socket supplies AC. (4 marks)

(d) Distinguish between preventive and corrective maintenance, giving one example of each. (4 marks)

(e) A technician is about to open a computer case to replace a component. State two safety precautions they must take first, and explain the specific risk each addresses. (5 marks)

Show worked answer

(a) V = I x R = 0.3 x 40 = 12 volts. (3 marks)

(b) DC (Direct Current) flows in one constant direction; AC (Alternating Current) periodically reverses direction. A computer's internal components (CPU, RAM, drives) run on DC because their circuitry requires a steady, one-directional current to function correctly; the Power Supply Unit (PSU) converts the wall socket's AC into the DC every internal component actually needs. (4 marks)

(c) A=0,B=0: output 1 (not all inputs are 1). A=0,B=1: output 1. A=1,B=0: output 1. A=1,B=1: output 0 (all inputs are 1, so NAND inverts AND's 1 to 0). (4 marks)

(d) Preventive maintenance is scheduled, routine work done before a fault occurs, for example dust removal and thermal paste renewal. Corrective maintenance is work done in response to an actual fault, for example diagnosing and replacing a failed hard drive. (4 marks)

(e) Power off and unplug the system before opening the case, addressing the risk of working on live power, which could cause electric shock or damage components. Wear an anti-static wrist strap (or touch a grounded metal surface), addressing the risk of electrostatic discharge (ESD), an invisible static charge that can permanently damage a sensitive component even without the technician feeling anything. (5 marks)