• Standard and Phillips Screwdrivers - various sizes
• IC ROM Puller - For upgrading BIOS chips
• Multimeter - A necessary tool for troubleshooting electrical issues such as the power supply. It can also be used to do a resistance test. When performing this test make sure that the power to the system is unplugged.

The following table shows the readings that you should see for various multimeter tests:

Some components of a PC are field replaceable and some are not. Common Field Replaceable Units(FRUs) are below:

• Monitor
• Keyboard
• Mouse
• Floppy Drive
• CDROM
• Hard Drives
• Printer
• Video Adapter
• Sound Card
• Network Card
• Motherboard
• Power Supply
• Processor
• CMOS Battery
• RAM

Beep codes vary depending on the manufacturer of the BIOS. Below are some of the common beep codes for an Award BIOS.

Below are the IBM error code families and the component that the error code relates to:

• Lost BIOS password - Most newer motherboards have a jumper that can be used to clear the CMOS memory. Typically this involves opening the PC, changing the jumper to a special setting, and then booting the PC. If the memory has been cleared, you power the PC down and put the jumper back to its previous position
• System clock is not keeping correct time - This is typically caused by the CMOS battery failing or running low voltage. Usually, replacing the CMOS battery will fix this.
• System locks up consistently a few minutes after power up - This is usually associated with a failed processor fan or general overheating. Boot the system with the case off and see if the fan is running. If not, the fan and likely the processor will need to be replaced.
• System appears completely dead(no visible activity during powerup) - Check the external power cable and make sure that it is plugged into a working outlet and securely plugged into the unit. Next, make sure that the on/off switch is set to "On" and that the 115/230 switch is set to the appropriate setting for your location. Verify that the internal power connection from the power supply to the motherboard is firmly connected. A multimeter can be used to narrow determine how far the power is getting. Start at the outlet and work your way inside. Finally, remove all unnecessary components from the motherboard to see if one of them is overloading the power supply.
• Front panel lights come on and the power supply fan runs, but no other activity is present - Try swapping out the power supply. If this doesn't fix the problem, remove all unnecessary components from the motherboard to see if one of them is overloading part of the power supply.

There are 2 types of memory errors:

• Soft-memory errors - These are occasional strange behaviors that can usually be cleared by rebooting.
• Hard-memory errors - Caused by a hardware failure related to the RAM and will usually display a message on the screen or create a beep code. Can be isolated by removing memory chips 1 at a time.

• System locks up while counting RAM - Usually requires that the processor be replaced

Keyboards can have a variety of symptoms including:
No characters appearing on the screen
6 beeps on boot
A 301 error code
Keyboard is locked - Unlock It error message
Keyboard Error - Keyboard Test Failure
KB/Interface Error - Keyboard Test Failure

The most common causes for these problems is:
Incorrect keyboard type in BIOS or Windows
Keyboard not properly connected
Blown fuse in back of keyboard


Mice:
Cursor skips around or gets stuck - This is usually caused by dirt and lint inside the mouse that needs to be cleaned.
Doesn't move at all - Can be a configuration error caused by an IRQ or address conflict, conflicting device drivers loaded in autoexec.bat and config.sys or can be caused by a hardware failure. If none of these are causing it, it is likely a problem with the port on the motherboard.

Video:

• There are a variety of problems that can occur from misconfigured drivers and settings. When possible, verify that the correct drivers are loaded and check for IRQ and memory address conflicts
• Screen goes blank after a while - This is usually due to Power Management settings in the BIOS
• The screen flickers - Usually caused by the refresh rate being set too low.
• The output on the screen is garbled or looks like a bunch of moving lines - This is most often caused by setting the resolution, color depth or refresh rate at a higher level than the monitor supports. To correct this, press F8 on boot and select "Safe Mode" from the menu. Set the display settings to appropriate levels.
• No display at all and you suspect hardware - Make sure that the monitor is plugged into a working outlet. Make sure that the contrast and brightness settings have not been turned all the way down. Make sure that the monitors signal cable is properly connected to the PC and that the video card is properly seated in the slot.

Floppy Drives:

• The floppy drive will not read any disks - Check for IRQ and memory address conflicts. Make sure that the internal power cable is connected from the power supply to the drive. Verify that the FDD cable is properly connected to the motherboard and the drive and that the pin 1 orientation is correct. You can also narrow down the problem by swapping out the drive and cable one at a time to determine if the problem is with one of them.
• The system will not boot from the floppy drive but works fine after boot - This is usually caused either by a problem with the floppy or by an incorrect boot sequence in the BIOS

Hard Drives:

• Make sure that the drive is properly connected and using the correct pin 1 orientation.
• Make sure that there is only one device connected to the cable that is configured as master.
• There are a variety of problems that can occur from misconfigured settings. Verify that the correct drive settings are reflected in the BIOS settings. Common error messages that can occur when these are incorrect are "Drive Type Mismatch" and "Invalid Media Type".
• Check for IRQ and memory address conflicts in Windows.
• The system will not boot. If booting from a floppy, the drive can be accessed from a DOS prompt - This usually indicates that the boot files are missing or corrupt. Change directories to the A drive(with the boot disk inserted) and type SYS C: to restore the boot files.
• From a DOS prompt, you receive a "Boot Disk Failure" or "Missing ROM Basic Interpreter" error message when trying to view the contents of the hard drive - Try restoring the master boot record by using the FDISK utility as follows: FDISK /MBR.
• If all configuration settings are correct and the drive cannot be accessed after booting with a boot disk and an "Invalid Drive" or Invalid Drive Specification" error message appears, the disk will need to be formatted and reconfigured.
• If the EIDE or IDE controller is dead and is hardwired to the system board, an IDE or EIDE controller expansion card can be used without having to replace the motherboard.
• If it is a SCSI drive, make sure that the hard drive is using a unique SCSI ID on its chain and that proper terminiation is in place.

CD-ROMS:

• Make sure that the drive is properly connected and using the correct pin 1 orientation.
• Make sure that there is only one device connected to the cable that is configured as master.
• Make sure that the drive is configured correctly in the autoexec.bat for a line similar to C:\MSCDEX.EXE /D:mscd001 /L:%CDROM% and config.sys for one like device=aspicd.sys /D:mscd001.
• If the CD tray has become jammed and will not open, use a paperclip or other long thin item into the tray release access hole.
• If the EIDE or IDE controller is dead and is hardwired to the system board, an IDE or EIDE controller expansion card can be used without having to replace the motherboard.
• If no sound is heard when playing a CD, make sure that the sound card is properly configured and that the cable is connected between the CD-ROM and the sound card.
• "Data error reading drive C:" or "Sector not found" error messages consistently occur - This is typically caused by a dirty drive that needs to be cleaned.

Modems:

• Check for I/O and IRQ conflicts
• You may need to configure a modem initialization string using the AT Command Set.
• Check configuration settings such as disabling call waiting or dialing a 9 first for an outside line.
• Refer to ISP instructions for advanced configuration options such as flow control, parity, etc.
• Make sure that the correct driver is loaded for the modem.
• As with any component, make sure that it is properly seated and all cables are correctly attached.

Preventative Maintenance
Cleaning of outer surfaces of a computer can be done with soap and water as long as the solution does not enter the internal parts of the computer. The solution should be applied with a lint-free cloth. The cleaning should be followed with an anti-static spray that can be made out of water and fabric softener.

Internal dust can be cleaned with canned air, a soft brush or anti-static vacuum. Anti-static vacuums are specially grounded to prevent static discharge like regular vacuums. Dust can contribute to overheating problems. Making sure that all expansion slot covers are in place can reduce dust buildup. Missing covers can also disrupt the airflow design of the case and cause overheating problems. Additional fans can be added to help cut down on internal temperature problems. Computer equipment should not be placed in areas of extreme temperature or humidity.

Oxidation corrosion can slow down or even prevent electricity from flowing through contact points. Oxidation buildup can be removed by rubbing with an emery board or eraser. It can also be cleaned with special cleaning solution.

Other internal components can be cleaned with Isopropyl alcohol and lint-free swabs.

Monitors should be cleaned with a soap and water solution with the power disconnected. Do not use household cleaning solutions as they can damage the screen. Monitors should not be opened unless you are qualified to work on them. Deadly voltage can be stored inside the monitor even a year after it has been turned off.

Computer components should be transported in antistatic foam or an anti-static bag.

Hard drives are vacuum sealed and should never be opened except by professionals in a "clean room".

Important data should be regularly backed up and stored in a fire-proof safe or at a separate location for protection against fire or theft. Windows NT/2000 Emergency Repair Disks should be stored in a secure place where only authorized personnel can access them.

Because floppy disks are magnetic media, they should not be exposed to magnetic fields that can be produced by TVs, monitors, speakers, power supplies and appliances with motors. Floppy drive heads can be cleaned with a wet or dry head cleaning disk. Keyboards can tend to collect dust between the keys. They can be vacuumed with a small vacuum.

Mice need to occasionally have the X and Y rollers cleaned with a lint-free swab.

Electrical spikes(measured in nanoseconds) or surges(measured in milliseconds) can cause damage to system components or even data loss. Surge suppressors can prevent minor variances in power and provide a stable stream of electricity to the unit, however, they may not always work against larger surges.

Uninterruptable Power Supplies(UPS) provide power to the devices connected to it for a period of time in the event of power loss or sag for long enough to gracefully shutdown the computer and avoid data loss. Unnecessary peripherals such as scanners and printers should not be connected to a UPS as they can overload it.

Laser printers have several hazards that should be noted. The laser can cause blindness, the fuser can cause burns and the power supply can cause electrocution.

Toner cartridges, ink jet cartridges and batteries can be recycled.

Hazardous materials come with Material Safety Data Sheets(MSDS) that provide a variety of information as to how the product should be handled and disposed of.

Electrostatic Discharge(ESD) can be harmful to electronic components and cause them to fail. Low humidity, walking across carpet and appliance motors are some of the common generators of ESD. MOS devices are particularly sensitive to ESD and special care should be taken around them. Below are some of the prevention methods employed to prevent damage:

• Grounding straps are connected to a technicians wrist. You can ground the wrist strap to the earth pin on a wall socket.
• Remove all metallic jewelery.
• Antistatic mats.
• Touching the chassis of the computer while plugged into a grounded outlet.
• Anti-static sprays can be applied to floors, computers and work surfaces.
• A humidifier can be used to keep the humidity above 50%.

An ESD wriststrap should never be worn when working with high voltage equipment such as monitors.

Computer equipment should be unplugged from the wall during electrical storms to prevent equipment damage and injury.

Printers
Font Types:

• Bitmap - composed of dots called pixels.
• Vector - Uses mathematical forulas to plot lines. Requires less storage space than bitmap.
• TrueType - Outline fonts for Windows only.

Feed Mechanisms:

• Pin Feed - Paper has perforated strip on each side that contains holes that fit onto pins that are rotated by a motor in the printer.
• Friction Feed - Typically uses rollers that press against the platen or drum that rotate forcing the paper through the printer.

Dot Matrix - Uses a matrix of pins to imprint an image. Uses a Ribbon. ROM programs the Fonts.

Troubleshooting:

• Smudges can be caused by the ribbon tension being too high
• Broken printhead pins can cause incomplete or missing characters.
• If the tops of characters are missing, the printhead is misaligned with the platen and needs to be reseated or the printhead carriage may need to be adjusted.
• If the print gets lighter on the page from left to right, the printhead distance from the plate is uneven and will need to be adjusted.

Ink Jet(or Bubble Jet) - No contact therefore quiet. Works by spraying ink onto the paper in a sequential fashion. Similar in operation to a dot matrix printer.

Troubleshooting:

• Never refill cartridges which are causing problems. The head is part of the cartridge so replace the entire cartridge.
• If the output is disfigured or wavy, make sure that the paper thickness level is in the correct position. If it is, then the paper feed rollers probably need to be replaced.

Laser Printers - Uses a Page Description Language (PDL) to print a page at a time. Main components are:

• Cleaning Blade - This rubber blade removes excess toner off the drum after the print process has completed.
• Photosensitive Drum - The core of the electrophotographic process. This component should not be exposed to light.
• Primary Corona Wire - Highly negatively charged wire erases the charge on the Photosensitive drum to make it ready for another image.
• Transfer Corona - A roller that contains a positively charged wire to pull the toner off the photosensitive drum and place it on the page.
• Toner - Plastic Resin. Naturally Negatively charged
• Fusing Rollers - Bonds the toner particles to prevent smearing. Uses heat to bond. A thermal fuse prevents the fuser from overheating.

Troubleshooting:

• Blank Pages - Can be caused by No Toner, Transfer Corona Failure or HVPS Failure.
• Speckled Pages - Due to a failure in the cleaning step of the EP Process. Or a scratch on the EP drum.
• Ghosted Images - Caused if the erasure lamp doesn’t erase all of the image from the EP drum before the next page is printed.
• Smudged Images - The fusing process must have failed. The heating elements in the fusing rollers may be faulty.
• Dark spots - Can indicated toner buildup at some point in the paper path. Running blank sheets through it may clear problem.
• Jams in laser printers usually occur in the paper pickup area, the fuser or the registration area. They can be caused by incorrect paper settings or media types.

Electrophotographic Print Process(EP):
The process concerned with putting the image on the page. Follows Six processes.

1. Cleaning - The Drum is cleaned and electrically erased.
2. Charging - The Drum is negatively charged to -5000Vdc. Done by the Primary Corona.
3. Writing - The Laser sweeps the length of the drum applying the image. The Laser reduces the negative charge on the drum where the image is going to be.
4. Developing - The Toner is transferred to the area on the drum which has been swept by the laser.
5. Transferring - Once the image is on the drum the paper is fed through and the transfer corona wire attracts the image from the drum to the paper.
6. Fusing - The Fusing rollers heat up and pass the paper through bonding the toner to the paper. Uses a Non stick roller surface.

Physical Connections:
Older printers utilize a RS-232 connection that can either be 9 or 25 pin serial port and cable. The cable should be less than 50 feet long(15.25 meters). Serial configuration requires that the port be configured with parity type, speed, protocol and character frame must be configured.

Parallel connections utilize a DB-25 port(left) on the computer to connect to the printer. Parallel cables should be less than 10 feet(3 meters).

Many newer printers also have rj-45 network connections and can be integrated with standard networks. Older models may have coaxial network connections. Another popular connection solution is the print server such as a Jet-Direct interface that connects to the printers parallel port and has an RJ-45 connection at the other end.

Scanners
Scanners are comprised of a Charge Coupled Device(CCD) array. This array is like a series of "eyes" that read and record light intensities and stores them in digital form. This is achieved when the scanners internal light source passes over the image that is being scanned.

Scanners come in three basic types. The simplest type of scanner is the hand held in which the scanning device is moved across images or text. The scanner reads the information directly. A Page scanner works by inserting a page into the top of the scanner which is pulled via rollers through the scanner. The most common type of scanner is the flatbed scanner which allows you to place a image or document on the top of its surface, much like a photocopier. Scanner quality is measured in DPI or dots per inch. 300 DPI is usually adequate for normal scanning, however, modern scanners can scan at resolutions of 9600 DPI and higher. The higher the resolution, the larger the resultant scanned file will be.

Scanners are connected to the system board via a SCSI, Parallel or other proprietary connection method depending on the scanner model.

Basic Networking
Network models are as follows:

• Peer-to-Peer - A peer to peer network is one in which lacks a dedicated server and every computer acts as both a client and a server. This is a good networking solution when there are 10 or less users that are in close proximity to each other. A peer to peer network can be a security nightmare, because the people setting permissions for shared resources will be computer idiots and the right people will never have access to the right resources. Thus is only recommended in situations where security is not an issue.
• Client/Server - This type of network is designed to support a large Number of users and uses dedicated server/s to accomplish this. Clients log on to the server/s in order to run applications or obtain files. Security and permissions can be managed by 1 or more administrators which cuts down on the aforementioned computer illiterates from medling with things that they shouldn't be. This type of network also allows for convenient backup services, reduces network traffic and provides a host of other services that come with the network operating system(NOS).
• Centralized - This is also a client/server based model that is most often seen in UNIX environments, but the clients are "dumb terminals" or "Diskless workstations". This means that the client may not have a floppy drive, hard disk or CDROM and all applications and processing occur on the server/s. As you can imagine, this requires fast and expensive server/s. Security is very high on this type of network.

Network Topologies

• Bus - This topology is older technology and essentially has each of the computers on the network daisy-chained to each other. This type of network is usually peer to peer and uses Thinnet(10base2) cabling. It is configured by connecting a "T-connector" to the network adapter and then connecting cables to the T-connectors on the computers on the right and left. At both ends of the chain the network must be terminated with a 50 ohm impedance terminator.
  ADVANTAGES: Cheap, simple to set up.
  DISADVANTAGES: Excess network traffic, a failure may affect many users, Problems are difficult to troubleshoot.
  

  

• Star - The star uses twisted pair(10baseT or 100baseT) cabling and requires that all devices are connected to a hub.
  ADVANTAGES: centralized monitoring, failures do not affect others unless it is the hub, easy to modify.
  DISADVANTAGES: If the hub fails then everything connected to it is down.
  

  

• Ring - The ring topology looks the same as the star, except that it uses special hubs and ethernet adapters. The Ring topology is used with Token Ring networks which are not very common.
  ADVANTAGES: Equal access.
  DISADVANTAGES: Difficult to troubleshoot, network changes affect many users, failure affects many users.
• Mesh - Mesh topologies are combinations of the above and are common on very large networks. For example, a star bus network has hubs connected in a row(like a bus network) and has computers connected to each hub.

Cabling
TYPES

Cable Type	Also Known As	Connector	Maximum Length
10Base5	RG-8 or RG-11, Thicknet coax	AUI/DIX	500 meters(1640 ft)
10Base2	RG-58, thinnet coax	BNC connector	185 meters(607 ft)
10BaseT	Cat 3, 4, 5 twisted pair	RJ-45	100 meters(328 ft)
100BaseT	Cat 5 twisted pair	RJ-45	100 meters(328 ft)
10baseFL	Fiber Optic	Fiber Optic connector	2 Kilometers(6562 feet)

Speed

Cable Type	Transmission Speed
Thicknet	10mbps
Thinnet	10 mbps
cat 2 twisted pair	4 mbps
cat 3 twisted pair	10 mbps
cat 4 twisted pair	16 mbps
cat 5 twisted pair	100 mbps
Fiber Optic	100 mbps - 1 gbps

Misc Cable Info

• Shielded twisted pair(STP) differs from UTP in that it has a foil jacket that helps prevent crosstalk. Crosstalk is overflow from an adjacent wire.
• Plenum grade cabling is required if the cabling will be run between the ceiling and the next floor(this is called the plenum). Plenum grade is resistant to fire and does not emit poisonous gasses when burned.
• Thicknet is often used as a backbone. A transceiver with a vampire tap penetrates the core of the cable. From the transceiver a DB-15 connector plugs into the AUI port on a given device.
• Fiber Optic cabling has an built in security as you can't intercept data as you can with other cable mediums.
• Baseband= Digital, single frequency, bidirectional communications and uses a repeater to regenerate signals.
• Broadband= Analog, multiple frequencies, unidirectional communications, uses amplifiers to boost signals.
• A Time Domain Reflectometer(TDR) can be used to find opens and shorts in cables.

Access Methods

• CSMA/CD - This stands for "carrier-sense multiple access with collision detection" and is the method used on ethernet networks whereby all computers on the network check the cable for traffic before attempting to transmit a packet. If more than 1 transmits at the same time then there will be a collision and both computers will wait a random amount of time and retransmit.
• CSMA/CA - Stands for "carrier-sense multiple access with collision avoidance". This access method prevents collisions by having computers broadcast an intent to send a packet. This is the access method used by Localtalk and is sometimes described as "chatty". This broadcasting of intent to send can cause excess network traffic and slow things down.
• Token Passing - Token passing is the access method used by token ring networks. With this method, a packet called a token is passed around the network. A computer that wishes to transmit must wait until it can take control of the token, allowing only one computer to transmit at a time. This is sort of like the "conch" in Lord of the Flies. Piggy had all of this crap that he wanted to whine about all of the time, but could only do so if he possessed the conch.
• Demand Priority - This access method is used with 100VG-AnyLAN networks. The repeaters, bridges, routers or hubs search the network for requests that are waiting to be sent. If 2 or more requests are received by the network hardware at once, the data with the highest priority is sent. Priority for different data types can be controlled by the administrator. A real advantage is that computers can receive and transmit at the same time with this access method.

Frame Types

802.1	Internetworking
802.2	Logical link control - LLC adds header information that identifies the upper layer protocols sending the frame.
802.3	Ethernet - Media Access Control (MAC) sub-layer uses Carrier Sense Multiple Access with Collision Detection(CSMA/CD)
802.4	Token bus LAN
802.5	Token Ring BUS
802.6	Metropolitan Area network (MAN)
802.7	Broadband
802.8	Fiber optic
802.9	Integrated voice/Data
802.10	Network Security
802.11	Wireless Networks
802.12	Demand Priority. Like 100VG-Any LAN

Network Cards and Protocols

• Like other expansion cards, network cards require that the appropriate driver is loaded to function properly.
• If an network card will not function it may be due to an IRQ or memory conflict. Typical settings for these are:
  • IRQ - 5
  • Port Address - 300h
  • Base Memory - D8000h
• ISA network cards are not PnP compatible and have to be manually configured.
• Network communication uses a set of "rules" called protocols. Common protocols on modern networks are IPX/SPX and TCP/IP. These protocols regulate how packets are packaged and sent across a network. If devices do not have the same protocols configured and there is no "middleman" to translate, they will not be able to communicate with each other.

PCMCIA
The PCMCIA bus was developed for smaller computing devices and is hot-swappable. There are 3 types of PCMCIA cards:

• Type I - 3.3mm thick and used as memory expansion units.
• Type II - 5mm thick and most expansion functions except removable hard drives. Type I cards will work in them.
• Type III - 10.5mm thick and used mainly for removable drives. Type I and II cards will work in them.