Help Desk: Desktop Computer Components and Repair

2026-09-20 · help-desk, tcm, class-notes

Electrostatic discharge (ESD) is the sudden flow of static electricity between two objects at different charge levels. You feel a shock at around 3,000 volts, but chips can be damaged by a few hundred — far below…

Class notes · TCM Security, Practical Help Desk · Section 4

Quick reference: the short version of this section is the Section 4 cheat sheet. Exam-depth hardware is in A+ Core 1.

Learning objectives

By the end of these notes you should be able to:

  1. Work inside a PC safely, avoiding electrostatic discharge and electrical hazards.
  2. Explain the role, key specifications and failure signs of the CPU, RAM, storage, PSU, GPU and motherboard.
  3. Install and replace each major component.
  4. Identify common ports, cables and peripherals.
  5. Describe the POST and boot process, and use BIOS/UEFI settings.
  6. Size a power supply with a worked calculation.
  7. Apply a structured troubleshooting method to hardware tickets.
  8. Inspect hardware from the command line before opening a case.

1. Safety and ESD

1.1 Electrostatic discharge

Electrostatic discharge (ESD) is the sudden flow of static electricity between two objects at different charge levels. You feel a shock at around 3,000 volts, but chips can be damaged by a few hundred — far below what you'll notice. Damage may be instant or latent: a component that fails weeks later.

Precaution

Why

Antistatic wrist strap clipped to bare metal on the chassis

Keeps you at the same potential as the PC

Antistatic mat

A safe, grounded work surface

Antistatic bags for parts

Shield components in storage

Handle boards by the edges

Avoid touching contacts and chips

Avoid carpets and wool

Big static generators

1.2 Electrical safety

  1. Shut down properly.
  2. Switch off at the PSU rocker and unplug the power cable.
  3. Press and hold the power button for about 5 seconds to drain residual charge.
  4. Never open a PSU. Its capacitors can hold a dangerous charge long after unplugging. A faulty PSU is replaced, not repaired.

1.3 Opening the case

2. The CPU

2.1 What it does

The central processing unit executes instructions: the fetch-decode-execute cycle from section 3.

2.2 Key specifications

Spec

Meaning

Why it matters

Cores

Independent processing units on one chip

More cores = more simultaneous work

Threads

Logical processors; SMT/Hyper-Threading gives 2 per core

Better multitasking throughput

Clock speed (GHz)

Cycles per second; base and boost speeds

Faster single-task performance

Cache (L1/L2/L3)

On-chip fast memory

Less waiting on RAM

TDP (watts)

Heat the cooler must remove

Sizes the cooler and PSU

Socket

The physical interface, e.g. Intel LGA 1700, AMD AM5

The CPU must match the board

Architecture

x86-64 (Intel/AMD) or ARM

Determines which software runs natively

2.3 Installing a CPU

  1. Open the socket: lift the retention arm and open the load plate.
  2. Orient the CPU: line up the small triangle on the CPU with the triangle on the socket (pin 1), and match the notches.
  3. Lower it straight down. Never press or slide it — bent socket pins are the classic disaster.
  4. Close the load plate and lever.
  5. Thermal paste: apply a pea-sized amount to the centre of the CPU's heat spreader. Coolers with pre-applied paste don't need more.
  6. Mount the cooler with even, diagonal tightening.
  7. Connect the fan to the CPU_FAN header.

2.4 CPU failure signs

3. RAM

3.1 What it does

Random access memory holds the programs and data in use right now. It's fast but volatile: everything is lost at power-off.

3.2 Key specifications

Spec

Meaning

Type / generation

DDR4 or DDR5 — keyed differently, not interchangeable

Form factor

DIMM (desktop) or SODIMM (laptop)

Capacity

8, 16 or 32 GB per module

Speed

MT/s, e.g. DDR4-3200, DDR5-5600

Channels

Matched modules in the right slots run in dual channel for more bandwidth

ECC

Error-correcting memory for servers; usually not supported by consumer boards

3.3 Installing RAM

  1. Check the motherboard manual for the recommended slots (for two modules, often A2 and B2).
  2. Open the clips at the slot ends.
  3. Line up the module's notch with the key in the slot.
  4. Press straight down, evenly, until both clips snap closed. Expect firm pressure.

3.4 Worked example — "PC slow since an upgrade"

Symptom: a user added a 16 GB module to their existing 8 GB one. The PC now shows 24 GB but games stutter.

  1. Check what's installed:

Get-CimInstance Win32_PhysicalMemory | Select-Object BankLabel, Capacity, Speed, ConfiguredClockSpeed1. Result: mismatched modules with different capacities, both running at the slower module's speed. Only part of the memory runs in dual channel. 2. Fix: a matched pair (2 × 16 GB) in the recommended slots.

3.5 RAM failure signs and tests

Sign

Test

Random blue screens, crashes, corrupted files

Windows Memory Diagnostic: run mdsched.exe, then reboot

Beeps or a DRAM debug LED at power-on

Reseat modules; test one module at a time

PC reports less RAM than installed

Reseat; check that slot; check the 32-bit OS limit

Deeper testing: MemTest86 from a bootable USB, left running for several passes.

4. Storage drives

4.1 Drive types

Type

How it stores data

Speed

Notes

HDD

Magnetic spinning platters and a moving read/write head

~100–250 MB/s

Cheap per TB; fragile when running; clicks when failing

SATA SSD

NAND flash chips

~550 MB/s (SATA limit)

Big upgrade over an HDD

NVMe SSD

NAND flash over PCIe lanes

3,000–7,000+ MB/s

Usually M.2; the modern default

Form factor / interface

Notes

3.5"

Desktop HDDs

2.5"

Laptop HDDs and SATA SSDs; 7 mm or 9.5 mm thick

M.2

A card shape, not a speed. Can be SATA or NVMe — check the slot supports the drive. Lengths 2230, 2242, 2280 (width × length in mm)

SATA cables

7-pin data plus 15-pin power

4.2 Drive health

SMART (Self-Monitoring, Analysis and Reporting Technology) is built into drives to predict failure.

Get-PhysicalDisk | Select-Object FriendlyName, MediaType, BusType, HealthStatus Get-PhysicalDisk | Get-StorageReliabilityCounter | Select-Object Temperature, Wear, ReadErrorsTotal sudo smartctl -a /dev/sda \

smartmontools package

4.3 Replacing a drive

  1. Back up or clone the data first.
  2. Mount the drive: screws or a tool-less caddy. M.2 drives need the standoff and retaining screw.
  3. Connect SATA data and power, or seat the M.2 at an angle and press it down.
  4. Initialise the new drive: Disk Management (diskmgmt.msc) → GPT → New Simple Volume.

5. The power supply (PSU)

5.1 What it does

The PSU converts mains AC (230 V in the UK) into the low-voltage DC rails the components need.

Rail

Wire colour

Powers

+12 V

Yellow

CPU, GPU, drive motors, fans — most of the load

+5 V

Red

Drives, USB

+3.3 V

Orange

Some motherboard circuits, M.2

Ground

Black

Return path

Connector

Goes to

24-pin ATX (20+4)

Motherboard

4/8-pin EPS (CPU)

CPU power, near the socket

6/8-pin PCIe, or 16-pin 12V-2x6

Graphics card

SATA power (15-pin)

SATA drives

Molex (4-pin)

Legacy devices, some fans

5.2 Worked example — sizing a PSU

Build: CPU rated at 125 W, graphics card at 220 W, plus motherboard, RAM, drives and fans at roughly 75 W.

  1. Estimated peak: 125 + 220 + 75 = 420 W.
  2. Add 30–50 % headroom (efficiency sweet spot, spikes, ageing): 420 × 1.3 ≈ 550 W; 420 × 1.5 = 630 W.
  3. Choose: a quality 550–650 W unit with an 80 PLUS Gold rating.

80 PLUS efficiency, in increasing order: White, Bronze, Silver, Gold, Platinum, Titanium.

5.3 PSU failure signs

Test with a PSU tester, or swap in a known-good unit.

6. The graphics card (GPU)

Integrated graphics

Dedicated (discrete) GPU

Built into the CPU; shares system RAM

Separate card with its own VRAM

Low power, fine for office work

Gaming, 3D, video editing, AI workloads

Video out from the motherboard ports

Video out from the card's ports

Installing a card:

  1. Remove the slot covers.
  2. Seat the card in the top PCIe x16 slot until the latch clicks.
  3. Screw it to the case.
  4. Connect the PCIe power cables.
  5. Plug the monitor into the card.
  6. Install the vendor driver.

In the real world: "new graphics card, no display" is one of the most common tickets. The monitor cable is still in the motherboard's port — and many boards turn integrated graphics off when a card is present.

7. The motherboard

7.1 Form factors

Form factor

Size

Expansion

ATX

305 × 244 mm

Most slots

microATX

244 × 244 mm

Fewer slots

Mini-ITX

170 × 170 mm

One PCIe slot, 2 RAM slots

A smaller board fits a larger case (mounting holes line up), but not the reverse.

7.2 Anatomy

+----------------------------------------------------------+ | [Rear I/O] [CPU socket] [RAM][RAM][RAM][RAM] [24pin] | | USB, LAN, | | | audio, [CPU_FAN] | | video | | [M.2 slot]--------------------------------------- | | [PCIe x16]======================================= [SATA] | | [PCIe x1 ]===== [SATA] | | [CMOS battery] [Chipset] [Front panel header] | +----------------------------------------------------------+

Part

Role

Chipset

Controls communication between CPU, storage, USB and slots

PCIe slots

x16 for GPUs; x1/x4 for network, sound and capture cards

M.2 slots

NVMe/SATA SSDs; some carry Wi-Fi cards

SATA ports

Drives

Headers

Front-panel buttons and LEDs, front USB, audio, fans

CMOS battery (CR2032)

Keeps the real-time clock and firmware settings when unplugged

Standoffs

Hold the board off the case; prevent short circuits

The front-panel header is fiddly. PWR_SW and RESET_SW have no polarity; the LED pins (PLED +/-, HDD LED +/-) do. Check the manual's diagram.

8. Ports, cables and peripherals

Port

Use

Notes

USB-A

Peripherals, storage

USB 2.0 (480 Mbps), 3.x (5–20 Gbps)

USB-C

Data, video, charging

Reversible; capabilities vary by port

HDMI

Monitors, TVs — video and audio

Digital

DisplayPort

Monitors — video and audio

Digital; common on PC GPUs

DVI / VGA

Older monitors

VGA is analog

RJ45

Ethernet

1 Gbps typical, 2.5 Gbps increasingly common

3.5 mm audio

Green = output, pink = mic, blue = line in

PS/2 (legacy)

Purple = keyboard, green = mouse

9. POST and the BIOS/UEFI

9.1 The boot sequence

  1. Power button pressed → PSU starts and sends "power good".
  2. The CPU starts running firmware (BIOS/UEFI) from a chip on the motherboard.
  3. POST (power-on self-test) checks the CPU, RAM and video.
  4. The firmware reads the boot order and finds a bootable device.
  5. The bootloader (Windows Boot Manager or GRUB) loads the operating system.

9.2 When POST fails

Indicator

Meaning

Beep codes

Patterns (e.g. long-short-short) that mean different things by firmware vendor — look them up in the board manual

Debug LEDs (CPU / DRAM / VGA / BOOT)

The stage where POST stopped

Two-digit POST code display

A specific error code, listed in the manual

9.3 BIOS vs UEFI

Legacy BIOS

UEFI

1980s design, 16-bit

Modern firmware

MBR disks, 2 TB boot limit

GPT disks, huge drives

Text-only setup

Graphical, mouse support

No Secure Boot

Secure Boot: only signed bootloaders run

Common settings: boot order; enable/disable Secure Boot; TPM (fTPM/PTT) on or off; virtualization (VT-x / AMD-V); XMP/EXPO memory profiles (run RAM at its rated speed); fan curves; date and time; firmware passwords.

Reset to defaults: use "Load optimized defaults" in setup, or clear the CMOS (a jumper, or remove the coin cell for a few minutes).

Firmware updates fix bugs and security flaws. Use only the vendor's file, and don't interrupt the flash.

10. Troubleshooting method and a Ticket Interrupt

10.1 The six steps

  1. Identify the problem. Question the user, reproduce it, and ask what changed.
  2. Establish a theory of probable cause. Question the obvious first.
  3. Test the theory. If it's wrong, form a new one, or escalate.
  4. Plan and implement the fix.
  5. Verify full functionality, and add preventive measures.
  6. Document findings, actions and outcome.

10.2 Worked example — "My PC won't turn on"

  1. Identify: is it completely dead, or do fans spin with no display? The user says nothing happens at all — no lights. They moved desks yesterday.
  2. Theory: power delivery — cable, wall socket, PSU switch, or the PSU itself. Starting obvious: a moved PC often loses a cable or has the rocker switch knocked.
  3. Test:
  4. Fix: replace the PSU (sized per section 5.2).
  5. Verify: the PC powers on, POSTs and boots. Check temperatures and run for a while.
  6. Document:

"No power after desk move; cable and socket OK; PSU tester showed no 12 V; replaced PSU (650 W Gold); verified boot; old PSU disposed of as e-waste."

11. Inspect hardware without opening the case

Need

Windows (PowerShell)

Linux

CPU

Get-CimInstance Win32_Processor | Select-Object Name, NumberOfCores, NumberOfLogicalProcessors, MaxClockSpeed

lscpu

RAM

Get-CimInstance Win32_PhysicalMemory | Select-Object BankLabel, Capacity, Speed

free -h and sudo dmidecode -t memory

Disks

Get-PhysicalDisk | Select-Object FriendlyName, MediaType, BusType, Size, HealthStatus

lsblk and sudo smartctl -a /dev/sda

GPU

Get-CimInstance Win32_VideoController | Select-Object Name, DriverVersion

lspci | grep -iE 'vga|3d'

Motherboard / BIOS

Get-CimInstance Win32_BaseBoard; Get-CimInstance Win32_BIOS

sudo dmidecode -t baseboard -t bios

Everything

msinfo32, dxdiag

sudo lshw -short

12. Security perspective

Summary

Glossary

Term

Definition

ESD

Electrostatic discharge — static that can damage components

Latent damage

ESD damage that causes failure later rather than immediately

Core / thread

A physical processing unit / a logical processor

TDP

Thermal design power — heat output a cooler must handle

Socket

The CPU's physical interface on the motherboard

Thermal paste

Compound that fills gaps between CPU and cooler

DIMM / SODIMM

Desktop / laptop memory module

Dual channel

Two matched modules working in parallel for bandwidth

XMP / EXPO

Memory profiles that set rated RAM speeds

NVMe

Fast SSD protocol over PCIe

M.2

Small card form factor for SSDs and Wi-Fi

SMART

Built-in drive health monitoring

PSU rail

A DC voltage output (+12 V, +5 V, +3.3 V)

80 PLUS

PSU efficiency certification tiers

VRAM

Memory on a graphics card

Chipset

Motherboard controller linking CPU, storage and I/O

Standoff

A spacer holding the motherboard off the case

CMOS battery

Coin cell powering the real-time clock and settings

POST

Power-on self-test run by firmware

UEFI

Modern firmware replacing BIOS; supports GPT and Secure Boot

Secure Boot

UEFI feature allowing only signed bootloaders

Review questions

  1. Why press the power button after unplugging, before working inside a PC?
  2. What must match between a CPU and a motherboard?
  3. A PC has 8 GB + 16 GB modules and games stutter. What's likely and what fixes it?
  4. Is an M.2 drive always faster than a 2.5" SSD? Explain.
  5. Calculate a sensible PSU size for a 105 W CPU, 285 W GPU and 80 W for everything else.
  6. Which PSU rail carries most of the load, and what colour are its wires?
  7. A user installs a graphics card and gets "no signal". What's the most likely cause?
  8. What does the CMOS battery do, and what's the symptom when it dies?
  9. Name three differences between legacy BIOS and UEFI.
  10. List the six troubleshooting steps in order.
  11. Which Windows tool tests RAM, and how do you launch it?
  12. Give three defences against an attacker with physical access to a desktop.

Answer key

  1. To drain residual charge from the PSU and board capacitors.
  2. The socket (e.g. AM5, LGA 1700) and chipset support for that CPU generation — sometimes needing a BIOS update.
  3. Mismatched modules, so only part of the memory runs in dual channel, at the slower speed. Fix: a matched pair (2 × 16 GB) in the recommended slots.
  4. No. M.2 is a form factor. An M.2 SATA drive is no faster than a 2.5" SATA SSD; only M.2 NVMe is faster.
  5. 105 + 285 + 80 = 470 W; × 1.3–1.5 = about 610–705 W. Choose a quality 650–750 W unit.
  6. +12 V, yellow.
  7. The monitor is plugged into the motherboard's video port instead of the graphics card.
  8. It keeps the real-time clock and firmware settings when the PC is unplugged. When it dies, the date/time resets and settings return to defaults at each power loss.
  9. Any three of: UEFI supports GPT and large boot drives; a graphical setup; Secure Boot; faster boot. BIOS uses MBR with a 2 TB boot limit.
  10. Identify, theorise, test, plan and implement, verify, document.
  11. Windows Memory Diagnostic — run mdsched.exe and reboot.
  12. Any three of: firmware password; Secure Boot with USB boot disabled; BitLocker full-disk encryption; chassis lock or intrusion detection; checking for hardware keyloggers.