Computer Hardware, Laptop Repairing and Networking

Common network cable types

Coaxial cable
Unshielded twisted pair
Fiber optic

1. Coaxial cable

Coaxial cable looks similar to the cable used to carry TV signal. A solid-core copper wire runs down the middle of the cable. Around that solid-core copper wire is a layer of insulation, and covering that insulation is braided wire and metal foil, which shields against electromagnetic interference. A final layer of insulation covers the braided wire.

There are two types of coaxial cabling: thinnet and thicknet. Thinnet is a flexible coaxial cable about ¼ inches thick. Thinnet is used for short-distance. Thinnet connects directly to a workstation’s network adapter card using a British Naval Connector (BNC). The maximum length of thinnet is 185 meters. Thicknet coaxial is thicker cable than thinnet. Thicknet cable is about ½ inch thick and can support data transfer over longer distances than thinnet. Thicknet has a maximum cable length of 500 meters and usually is used as a backbone to connect several smaller thinnet-based networks.

The bandwidth for coaxial cable is 10 mbps (mega bits per second).

2. Unshielded Twisted Pair Cable

Twisted-pair cable is the most common type of cabling you can see in today’s LAN networks. A pair of wires forms a circuit that can transmit data. The pairs are twisted to provide protection against crosstalk, the noise generated by adjacent pairs. When a wire is carrying a current, the current creates a magnetic field around the wire. This field can interfere with signals on nearby wires. To eliminate this, pairs of wires carry signals in opposite directions, so that the two magnetic fields also occur in opposite directions and cancel each other out. This process is known as cancellation. Two Types of Twisted Pairs are Shielded Twisted Pair (STP) and Unshielded Twisted Pair (UTP).

Unshielded twisted-pair (UTP) cable is the most common networking media. Unshielded twisted-pair (UTP) consists of four pairs of thin, copper wires covered in color-coded plastic insulation that are twisted together. The wire pairs are then covered with a plastic outer jacket. The connector used on a UTP cable is called a Registered Jack 45 (RJ-45) connector. UTP cables are of small diameter and it doesn’t need grounding. Since there is no shielding for UTP cabling, it relies only on the cancellation to avoid noise.

UTP cabling has different categories. Each category of UTP cabling was designed for a specific type of communication or transfer rate. The most popular categories in use today is 5, 5e and 6, which can reach transfer rates of over 1000 Mbps (1 Gbps).

3. Fiber Optical Cabling

Optical Fiber cables use optical fibers that carry digital data signals in the form of modulated pulses of light. An optical fiber consists of an extremely thin cylinder of glass, called the core, surrounded by a concentric layer of glass, known as the cladding. There are two fibers per cable—one to transmit and one to receive. The core also can be an optical-quality clear plastic, and the cladding can be made up of gel that reflects signals back into the fiber to reduce signal loss.

There are two types of fiber optic cable: Single Mode Fiber (SMF) and Multi Mode Fiber (MMF).

1. Single Mode Fiber (SMF) uses a single ray of light to carry transmission over long distances.

2. Multi Mode Fibers (MMF) uses multiple rays of light simultaneously with each ray of light running at.

UTP Categories

Category 1	Voice only (Telephone)
Category 2	Data to 4 Mbps (Local talk)
Category 3	Data to 10Mbps (Ethernet)
Category 4	Data to 20Mbps (Token ring)
Category 5 Category 5e	Data to 100Mbps (Fast Ethernet) Data to 1000Mbps (Gigabit Ethernet)
Category 6	Data to 2500Mbps (Gigabit Ethernet)

RJ45 connector

Types of Cable Color Coding

There are two types of cable color coding.

1. Cross Cable (To connect same devices we will use cable. Example: PC to PC &
Switch to Switch)

2. Straight Cable (To connect different devices we will use straight cable. Example:

PC to switch, PC to Router)

Cross Cable Color Coding

A	B
Orange White	Green White
Orange	Green
Green White	Orange White
Blue	Blue
Blue White	Blue White
Green	Orange
White Brown	Brown White
Brown	Brown

Straight Color Coding

A	A
Orange White	Orange White
Orange	Orange
Green White	Green White
Blue	Blue
Blue White	Blue White
Green	Green
White Brown	White Brown
Brown	Brown

B	B
Green White	Green White
Green	Green
Orange White	Orange White
Blue	Blue
Blue White	Blue White
Orange	Orange
Brown White	Brown White
Brown	Brown

CAPACITOR

Capacitor “OR” Condenser “OR” Filter

Capacitor is an electronic component that stores electric charge. The capacitor is made of 2 close conductors (usually plates) that are separated by a dielectric material. The plates accumulate electric charge when connected to power source. One plate accumulates positive charge and the other plate accumulates negative charge.

Electrical or electronic device that (like a battery) stores electric current for releasing it at a specific time or rate but (unlike a battery) does not generate it. Also called condenser.

Capacitors are components that are used to store an electrical charge and are used in timer circuits. A capacitor may be used with a resistor to produce a timer. Sometimes capacitors are used to smooth a current in a circuit as they can prevent false triggering of other components such as relays. When power is supplied to a circuit that includes a capacitor - the capacitor charges up. When power is turned off the capacitor discharges its electrical charge slowly.

The capacitance is measured in units of Farad (usually in microfarad [μF]).

Farad

Farad is the unit of capacitance. It is named after Michael Faraday.

The farad measures how much electric charge is accumulated on the capacitor.

There are four types of Capacitor

Normal Polar Capacitor
Normal Non-Polar Capacitor
Micro Polar Capacitor
Micro Non-Polar Capacitor

1. Normal Polar Capacitor

Symbol

Checking

Meter Set X10 and Capacitor Discharge.Meter Positive Probe Connect on Capacitor Positive Leg and Meter Negative Probe Connect on Capacitor Nagative Leg.Meter Show Reading and back Zero Reading Capacitor it's ok.

2. Normal Non-Polar Capacitor

This is used in both directions.

Symbol

Checking

Analog Meter is set x10 then Non Polar Capacitor doesn’t Reading on Meter its ok.

3. Micro Polar Capacitor

Checking

A good indication for MICRO POLAR CAPACITOR shows the meter needle deflecting towards zero it's OK.

4. Micro Non-Polar Capacitor

Checking

A defective indication for an MICRO NON-POLAR CAPACITOR shows that the meter will rest on zero it's OK.

Laptop Rpairing

STEP 1---------- Battery

Being by turning the laptop over so that you can see the bottom of the computer.

STEP 2

Slide the battery release switch to the right while simultaneously lifting up the battery.

STEP 3 ---------- Fans

Loosen the screws around the plate and remove the plate.

STEP 4

Remove the screws from the plate covering the fans.

STEP 5

Ø Lift the plate and lower fan off the heat sing being careful not to damage the lower fan cables, which is attached to the motherboard.

Ø Disconnect the lower fan connector from the motherboard.

Ø Remove the metal plate and lower fan.

Ø The lower fan will easily separate from the metal plate.

STEP 6

Ø Disconnect the upper fan connector from the motherboard.

Ø Remove the spring loaded screws holding the heat sink assembly to the motherboard.

STEP 7

Ø Slide the heat sink assembly including the upper fan out by pulling it down and left simultaneously.

Ø When reinstalling heat sink, ensure it is thoroughly cleaned and the thermal ensure proper thermal contact with the devices on the logic board to prevent thermal issues.