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Transcript
OBJECTIVES 1. Demonstrate proper cleaning procedures for various system components. 2. Describe electrostatic discharge hazards and methods of preventing ESD. 3. List the steps for proper IC handling. 4. Define the term ground. 5. Describe the two types of uninterruptible power supplies (UPS) and state their qualities. 6. State typical precautions that should be observed when working on computer equipment. 7. Perform generic preventive maintenance routines as required (for example, remove excess toner, defragment hard drives, and create back-up copies). 8. Detail routine preventive maintenance procedures as they apply to hard and floppy disks. 9. Perform basic disk management functions on a hard drive, including using ScanDisk, CHKDSK, and Defrag utilities. 10. Use backup software to create backups of important data. 11. Use software utilities to identify and remove viruses from computer systems. 12. List precautionary steps that should be taken when handling floppy disks. (continued) OBJECTIVES (CONTINUED) 13. List steps to clean a dot-matrix, ink-jet, or laser printer. 14. Establish and maintain preventive maintenance schedules for users. 15. Differentiate between various UPS specifications and state how they apply to a given situation. 16. State potential hazards that are present when working with laser printers, monitors, and other equipment. Identify the purpose of various types of preventive maintenance measures, products and procedures, and when and how to use them. Content may include the following: Liquid cleaning compounds Types of materials to clean contacts and connections Non-static vacuums (chassis, power supplies, fans) Cleaning monitors Cleaning removable media devices Ventilation, dust, and moisture control on the PC hardware interior. (continued) Identify the purpose of various types of preventive maintenance measures, products and procedures, and when and how to use them. Content may include the following: (continued) Hard disk maintenance (defragging, ScanDisk, CHKDSK) Verifying UPS (Uninterruptible Power Supply) and suppressors Cleaning is a major part of keeping a computer system healthy. Therefore, the technician’s tool kit should also contain a collection of cleaning supplies. Along with hand tools, it will need a lint-free, soft cloth (chamois) for cleaning the plastic outer surfaces of the system. TEST TIP Know the common methods of cleaning various computer components. TEST TIP Know what types of materials/techniques can be used to clean different areas of the computer system. Figure 8-1: How to Handle a PC Board The environment around a computer system and the manner in which the computer is used determine greatly how many problems it will have. Occasionally dedicating a few moments of care to the computer can extend its Mean Time Between Failures (MTBF) period considerably. This activity, involving maintenance not normally associated with a breakdown, is called Preventive Maintenance (PM). TEST TIP Know what environmental conditions or activities are most likely to lead to equipment failures. TEST TIP Be aware of the effect that missing expansion slot covers have on the operation of the system unit. TEST TIP Know that computer vacuums have special grounding to dissipate static buildup that can damage computer devices. CHALLENGE #1 When you arrive at a customer’s office to repair one of their key computers, you trace the problem down to a defective microprocessor. The system has apparently been upgraded several times over its lifetime there are several open expansion slots and loose cables inside the system unit. There is also a layer of dust on all the internal components. What should you tell the manager when she asks you about what you have found? Figure 8-2: Caution Areas Inside the Monitor Figure 8-3: Proper Packing of a Hard Drive for Shipment Figure 8-4: Data Backup Systems TEST TIP Be aware of the precautions that should be employed with storing system backups. Unlike hard-disk drives, tape drives, floppy drives, and CD-ROM/DVD drives are at least partially open to the atmosphere, and their media may be handled on a regular basis. This opens these drive units up to a number of maintenance concerns not found in hard disk drives. Also, the removable cartridges, disks, or discs can be adversely affected by extremes in temperature, exposure to magnetic and electromagnetic fields, bending, and airborne particles that can lead to information loss. Figure 8-5: Cleaning the R/W Heads Input peripherals generally require very little in the way of preventive maintenance. An occasional dusting and cleaning should be all that’s really required. There are, however, a few common-sense items to keep in mind when using an input device that should prevent damage to the device, and ensure its longevity. TEST TIP Remember that dust can settle into the keyboard through the cracks between the keys. Figure 8-6: Cleaning the Keyboard Figure 8-7: Cleaning the Rollers in a Mouse TEST TIP Know how to clean a trackball mouse. Because printers tend to be much more mechanical than other types of computer peripherals, they require more effort to maintain. Printers generate pollutants, such as paper dust and ink droplets, in everyday operation. These pollutants can build up on mechanical parts and cause them to wear. As the parts wear, the performance of the printer diminishes. Therefore, printers require periodic cleaning and adjustments to maintain good performance. WARNING Cleaning the printer and its mechanisms periodically adds to its productivity by removing contaminants that cause wear. Vacuum the inside of the unit, after applying antistatic solution to the vacuum’s hose tip. Wipe the outside with a damp cloth, also using antistatic solution. Brush any contaminant buildup from the printer’s mechanical components, using a soft-bristled brush. Never lubricate the platen assembly of the printer. The steps to cleaning a dot-matrix printer are described in the following steps: 1 Adjust the printhead spacing. 2 Check the tension on the printhead positioning belt. 3 Clean the printer and its mechanisms. 4 Clean the printer’s roller surfaces. 5 Clean the surface of the platen. 6 Clean the surface of the dot-matrix printhead. (continued) The steps to cleaning a dot-matrix printer are described in the following steps: (continued) 7 Clean the paper-handling motor’s gear train. 8 Apply light oil to the gears using a swab. 9 Turn the platen to distribute the oil. 10 Apply a light coating of oil to the rails. 11 Move the carriage assembly to distribute the oil. The steps to cleaning an ink-jet printer are provided by the following steps: 1 Adjust the printhead spacing. 2 Check the tension on the printhead positioning belt. 3 Clean the printer and its mechanisms. 4 Clean the printer’s roller surfaces. 5 Clean the surface of the platen. 6 Clean the surface of the ink-jet printhead. (continued) The steps to cleaning an ink-jet printer are provided by the following steps: 7 Clean the paper-handling motor’s gear train. 8 Apply light oil to the gears using a swab. 9 Turn the platen to distribute the oil. 10 Apply a light coating of oil to the rails. 11 Move the carriage assembly to distribute the oil. TEST TIP Remember acceptable methods for cleaning laser printers. Steps to cleaning a laser printer are described in the following hands-on activity: 1 Remove dust build-up, and excess toner, from the interior. 2 Clean the laser printer’s rollers. 3 Clean the paper-handling motor’s gear train. 4 Apply light oil to the gears, using a swab. 5 Distribute the oil throughout the gear train. 6 Clean the corona wires. Check for other sources of heat buildup around the computer and its peripherals. These sources include: Direct sunlight from an outside window Locations of portable heaters in the winter Papers/books piled up around the equipment Identify various types of preventive maintenance measures, products, and procedures and when and how to use them. Content may include the following: Verifying UPS (uninterruptible power supply) and suppressors Avoid power variations Digital systems tend to be sensitive to power variations and losses. Even a very short loss of electrical power can shut a digital computer down, resulting in a loss of any current information that has not been saved to a mass storage device. Typical power supply variations fall into two categories: Transients — an over-voltage condition, while sags are an under-voltage condition. Over-voltage conditions can be classified as spikes (measured in nanoseconds), or as surges (measured in milliseconds). Sags — can include voltage sags and brownouts. A voltage sag typically lasts only a few milliseconds, while a brownout can last for a protracted period of time. TEST TIP Be aware of how undervoltage and overvoltage situations are categorized (i.e., time lengths). There are two factors to consider when choosing a surge suppresser: Clamping speed Clamping voltage TEST TIP Know what type of devices will protect systems from minor power sags and power surges. TEST TIP Know what type of device prevents power interruptions that can corrupt data. Uninterruptible power supplies are battery-based systems that monitor the incoming power and kick in when unacceptable variations occur in the power source. The term UPS is frequently used to describe two different types of power backup systems. Figure 8-8: UPS System Figure 8-10: Connecting the UPS in the System NOTE High-power-consumption peripheral devices, such as laser printers, should not be connected directly to the UPS. These devices can overload the UPS and cause data loss. If the UPS system does not come on, there are several items that should be checked. These items include: The On/Off switch The commercial AC power supply The UPS input circuit breaker The UPS battery connector TEST TIP Remember that nonessential peripheral devices should not be connected to UPS supplies. NOTE Of course, you should be aware that any UPS testing should be performed while the computer is not in active use and when there is no chance of data loss due to unexpected test results. TEST TIP Be aware that the UPS system will not be able to control the operation of the computer without the serial communications cable installed. TEST TIP Know that the best device for transporting computer equipment is the original manufacturer’s packaging, including the antistatic foam and bags used to pack it. Identify various safety measures and procedures, and when/how to use them. Content may include the following: Situations that could present a danger or hazard Potential hazards and proper safety procedures relating to: High-voltage equipment Power supply CRTs In most IBM compatibles, there are only two potentially dangerous areas. One of these is inside the CRT display, and the other is inside the power supply unit. Both of these areas contain electrical voltage levels that are lethal. However, both of these areas reside in self-contained units, and you will usually not be required to open either unit. TEST TIP Be aware of the voltage levels that are present inside a CRT cabinet. Laser printers contain many hazardous areas. The laser light can be very damaging to the human eye. In addition, there are multiple high-voltage areas in the typical laser printer, and a hightemperature area to contend with as well. TEST TIP Know the areas of the computer system that are dangerous for personnel and how to prevent injury from these areas. TEST TIP Remember the type of fire extinguisher that must be used with electrical systems, such as a PC. Identify environmental protection measures and procedures, and when/how to use them. Content may include the following: Special disposal procedures that comply with environmental guidelines Batteries CRTs Chemical solvents and cans MSDS (Material Safety Data Sheet) Most computer components contain some level of hazardous substances. Printed circuit boards consist of plastics, precious metals, fiberglass, arsenic, silicon, gallium, and lead. CRTs contain glass, metal, plastics, lead, barium, and rare earth metals. Batteries from portable systems can contain lead, cadmium, lithium, alkaline manganese, and mercury. TEST TIP Remember that toner cartridges from a laser printer should be recycled. TEST TIP Remember that the proper disposal method for batteries is to recycle them. The MSDS contains information about: What the material is Its hazardous ingredients Its physical properties Fire and explosion data Reactivity data Spill or leak procedures Health hazard information Any special protection information Any special precaution information Identify various safety measures and procedures, and when/how to use them. Content may include the following: ESD (Electrostatic Discharge) precautions and procedures What ESD can do, how it may be apparent or hidden Common ESD protection devices What is ESD Electrostatic Discharges (ESD) are the most severe form of Electromagnet Interference (EMI). The human body can build up static charges that range up to 25,000 volts. These buildups can discharge very rapidly into a electrically grounded body, or device. Placing a 25,000volt surge through any electronic device is potentially damaging to it. TEST TIP Remember what the acronym ESD stands for. The most common causes of ESD are: Moving people Improper grounding Unshielded cables Poor connections Moving machines Low humidity (hot and dry conditions) TEST TIP Memorize the conditions that make ESD more likely to occur. TEST TIP Be aware that compressed air can be used to blow dust out of components and that it does not create ESD. TEST TIP Memorize conditions and actions that produce electrostatic discharge. You may be a little confused by the fact that we warn you about the lethal 25,000 volts present inside the monitor and then say that the 10,000 to 25,000 volts of ESD is not harmful to humans. The reason for this is the difference in current-delivering capabilities created by the voltage. For example, the circuitry in the monitor and the power supply is capable of delivering amps of current, while the currentproducing capability of the electrostatic charge is less than a thousandth of that. Therefore, the 120 Vac, 1-amp current produced by the power supply unit is lethal, while the 25,000 Vdc, microamps of current produced by ESD is not. TEST TIP Remember that the current capabilities of electrical devices establish the potential danger levels associated with working around them. CHALLENGE #2 You have been asked to consult on the design of your company’s new repair facility near Phoenix, Arizona. In particular, management wants to know how to equip the work areas of their new facility. You have not been to the site, but you know that it is in a hot desert environment. Also, the building will be air-conditioned. How should you advise them about precautions that should be taken with the work area? Figure 8-10: Typical Antistatic Devices TEST TIP Know when not to wear an antistatic wrist strap. To avoid damaging static-sensitive devices, the following procedures will help to minimize the chances of destructive static discharges: Before touching any components inside the system, touch an exposed part of the chassis or the power supply housing with your finger. Grounding yourself in this manner will ensure that any static charge present on your body is removed. This technique should be used before handling a circuit board or component. Of course, you should be aware that this technique will only work safely if the power cord is attached to a grounded power outlet. The ground plug on a standard power cable is the best tool for overcoming ESD problems. (continued) Figure 13-8: Discharging Through the Power Supply Unit To avoid damaging static-sensitive devices, the following procedures will help to minimize the chances of destructive static discharges: (continued) Do not remove ICs from their protective tubes (or foam packages) until you are ready to use them. If you remove a circuit board or component that contains static-sensitive devices from the system, place it on a conductive surface, such as a sheet of aluminum foil. (continued) To avoid damaging static-sensitive devices, the following procedures will help to minimize the chances of destructive static discharges: (continued) In the event that you have to replace a hard-soldered IC, you may want to install an IC socket along with the chip. Be aware that normal operating vibrations and temperature cycling can degrade the electrical connections between ICs and sockets over time. This gradual deterioration of electrical contact between chips and sockets is referred to as chip creep. It is a good practice to reseat any socket-mounted devices when handling a printed circuit board. Before removing the IC from its protective container, touch the container to the power supply of the unit in which it is to be inserted. (continued) TEST TIP Be aware of the effects that temperature cycling can have on socket-mounted devices. To avoid damaging static-sensitive devices, the following procedures will help to minimize the chances of destructive static discharges: (continued) Use antistatic sprays or solutions on floors, carpets, desks, and computer equipment. An antistatic spray or solution, applied with a soft cloth, is an effective deterrent to static. Install static-free carpeting in the work area. You can also install an antistatic floor mat as well. Install a conductive tabletop to carry away static from the work area. Use antistatic tablemats. (continued) To avoid damaging static-sensitive devices, the following procedures will help to minimize the chances of destructive static discharges: (continued) Use a room humidifier to keep the humidity level above 50% in the work area. The term ground is often a source of confusion for the novice, because it actually encompasses a collection of terms. Generically, ground is simply any point from which electrical measurements are referenced. However, the original definition of ground actually referred to the ground. This ground is called earth ground. Figure 8-12: Power Transmission System Figure 8-13: Grounds on IC Chips TEST TIP Remember that ESD is destructive and EMI is not. TEST TIP Know the best protection for a computer system during an electrical storm. There are basically three types of viruses, based on how they infect a computer system: A boot-sector virus - This type of virus copies itself onto the boot sector of floppy and hard disks. The virus replaces the disk’s original boot-sector code with its own code. This allows it to be loaded into memory before anything else is loaded. Once in memory, the virus can spread to other disks. (continued) There are basically three types of viruses, based on how they infect a computer system: (continued) A file infector - File infectors are viruses that add their virus code to executable files. After the file with the virus is executed, the virus spreads to other executable files. A similar type of virus, called a macro virus, hides in the macro programs of word processing document files. These files can be designed to load when the document is opened or when a certain key combination is entered. In addition, these types of viruses can be designed to stay resident in memory after the host program has been exited (similar to a TSR program), or they might just stop working when the infected file is terminated. (continued) There are basically three types of viruses, based on how they infect a computer system: (continued) A Trojan horse - This type of virus appears to be a legitimate program that might be found on any system. Trojan horse viruses are more likely to do damage by destroying files, and they can cause physical damage to disks. TEST TIP Know how the different types of viruses attack the system. Typical virus symptoms include the following: Hard disk controller failures. Disks continue to be full even when files have been deleted. System cannot read write-protected disks. The hard disk stops booting and files are corrupted. The system will boot to floppy disk, but will not access the HDD. An Invalid Drive Specification message usually displays when attempting to access the C: drive. (continued) Typical virus symptoms include the following: (continued) CMOS settings continually revert to default even though the system board battery is good. Files change size for no apparent reason. System operation slows down noticeably. Blank screen when booting (flashing cursor). Windows crashes. The hard drive is set to DOS compatibility, and 32-bit file access suddenly stops working. Network data transfers and print jobs slow down dramatically. TEST TIP Know how viruses are spread. CHALLENGE #3 A customer calls you to his site complaining that the wide-carriage, dot-matrix printer in his accounting department is running very slowly and that they cannot get all their invoices printed for today’s shipping purposes. When you check their print queue, you see that the print jobs for the invoices are stacked up in the queue but are being processed. The accounting manager tells you that they typically don’t have any problems getting their invoices printed and that nothing out of the ordinary has been done to the computer to make it slow down. What items should you check to determine the cause of the slowdown? KEY POINTS Cleaning is a major part of keeping a computer system healthy. Therefore, the technician’s tool kit should also contain a collection of cleaning supplies. Along with hand tools, it will need a lint-free, soft cloth (chamois) for cleaning the plastic outer surfaces of the system. KEY POINTS The environment around a computer system and the manner in which the computer is used determine greatly how many problems it will have. Occasionally dedicating a few moments of care to the computer can extend its Mean Time Between Failures (MTBF) period considerably. This activity, involving maintenance not normally associated with a breakdown, is called Preventive Maintenance (PM). KEY POINTS Unlike hard-disk drives, floppy drives are at least partially open to the atmosphere, and they may be handled on a regular basis. This opens floppy-disk drives to a number of maintenance concerns not found in hard-disk drives. Also, the removable disks are subject to extremes in temperature, exposure to magnetic and electromagnetic fields, bending, and airborne particles that can lead to information loss. KEY POINTS Input peripherals generally require very little in the way of preventive maintenance. An occasional dusting and cleaning should be all that’s really required. KEY POINTS Because printers tend to be much more mechanical than other types of computer peripherals, they require more effort to maintain. Printers generate pollutants, such as paper dust and ink droplets, in everyday operation. These pollutants can build up on mechanical parts and cause them to wear. As the parts wear, the performance of the printer diminishes. Therefore, printers require periodic cleaning and adjustments to maintain good performance. KEY POINTS Digital systems tend to be sensitive to power variations and losses. Even a very short loss of electrical power can shut a digital computer down, resulting in a loss of any current information that has not been saved to a mass storage device. KEY POINTS Uninterruptible power supplies are batterybased systems that monitor the incoming power and kick in when unacceptable variations occur in the power source. The term UPS is frequently used to describe two different types of power backup systems. KEY POINTS In most IBM compatibles, there are only two potentially dangerous areas. One of these is inside the CRT display, and the other is inside the power supply unit. Both of these areas contain electrical voltage levels that are lethal. However, both of these areas reside in self-contained units, and you will usually not be required to open either unit. KEY POINTS Laser printers contain many hazardous areas. The laser light can be very damaging to the human eye. In addition, there are multiple high-voltage areas in the typical laser printer, and a high-temperature area to contend with as well. KEY POINTS Most computer components contain some level of hazardous substances. Printed circuit boards consist of plastics, precious metals, fiberglass, arsenic, silicon, gallium, and lead. CRTs contain glass, metal, plastics, lead, barium, and rare earth metals. Batteries from portable systems can contain lead, cadmium, lithium, alkaline manganese, and mercury. KEY POINTS Electrostatic Discharges (ESD) are the most severe form of Electromagnet Interference (EMI). The human body can build up static charges that range up to 25,000 volts. These buildups can discharge very rapidly into a electrically grounded body or device. Placing a 25,000-volt surge through any electronic device is potentially damaging to it. KEY POINTS In general, MOS devices are sensitive to voltage spikes and static electricity discharges. This can cause many problems when you have to replace MOS devices, especially Complementary-Symmetry Metal Oxide Semiconductor (CMOS) devices. The level of static electricity present on your body is high enough to destroy the inputs of a CMOS device if you touch its pins with your fingers. KEY POINTS The term ground is often a source of confusion for the novice, because it actually encompasses a collection of terms. Generically, ground is simply any point from which electrical measurements are referenced. However, the original definition of ground actually referred to the ground. This ground is called earth ground. REVIEW QUESTIONS 1 List the two most dangerous areas of a typical microcomputer system, and explain why they are so dangerous. REVIEW QUESTIONS 2 Name three devices used to minimize ESD in the repair area. REVIEW QUESTIONS 3 The best general-purpose cleaning tool for computer equipment is _______. REVIEW QUESTIONS 4 List at least three environmental conditions that can adversely affect microcomputer equipment. REVIEW QUESTIONS 5 A short undervoltage condition, lasting milliseconds, is called ________. REVIEW QUESTIONS 6 Are there any restrictions on disposing of a spent toner cartridge? REVIEW QUESTIONS 7 Which type of IC device is most likely to be damaged by ESD? REVIEW QUESTIONS 8 Can an effective ESD strap be constructed by simply wrapping a grounded bare wire around your wrist? REVIEW QUESTIONS 9 What is the most effective method of dealing with EMI problems? REVIEW QUESTIONS 10 The best method of protecting computer equipment from a thunderstorm is to _______. REVIEW QUESTIONS 11 The best method for transporting electronic devices is _________. REVIEW QUESTIONS 12 List computer-related PM items that should be performed annually. REVIEW QUESTIONS 13 Name two characteristics that should be checked carefully before purchasing a UPS for a given computer system. REVIEW QUESTIONS 14 Describe the normal duration of a voltage spike. REVIEW QUESTIONS 15 Once a virus has infected a computer, where does it normally reside? EXAM QUESTIONS 1 Do viruses normally attack the system’s CMOS settings? a. Yes, this is how a virus attacks most computers. b. No, viruses do not normally attack CMOS settings. c. Yes, this is how viruses attack all computers. d. No, viruses never attack CMOS settings. EXAM QUESTIONS 2 How are most computer viruses spread from computer to computer? a. By downloading programs from networks b. By sharing infected files between individuals c. By not formatting disks before use d. By transferring files over modems EXAM QUESTIONS 3 What is the most common cause of ESD in microcomputer systems? a. Moving people b. High humidity c. Rubber mats d. Grounded power supply cables EXAM QUESTIONS 4 Where would it be inappropriate to use an ESD wrist strap? a. While working on hard-disk drives b. While working on system boards c. While working on CRT video monitors d. While working on printers EXAM QUESTIONS 5 What is one of the best methods for protecting computer systems from ESD? a. A water and fabric softener solution b. A water and ammonia solution c. A water and bleach solution d. A hydrogen tetrachloride solution EXAM QUESTIONS 6 A short overvoltage occurrence (nanoseconds) is called ________. a. a spike b. a surge c. a brownout d. a sag EXAM QUESTIONS 7 ESD is most likely to occur during periods of _________. a. low humidity b. high humidity c. medium humidity d. rain EXAM QUESTIONS 8 The best protection against powerfailure data loss is _______. a. a tape backup b. a surge suppresser c. a UPS d. a line filter EXAM QUESTIONS 9 Define a voltage sag. a. An overvoltage condition that lasts for a few milliseconds b. An undervoltage condition that lasts for an extended period c. An overvoltage condition that lasts for an extended period d. An undervoltage condition that lasts for a few milliseconds EXAM QUESTIONS 10 The most effective grounding system for a microcomputer is _________. a. an ESD wrist or ankle strap b. the safety ground plug at a commercial AC receptacle c. the ground plane of the system board d. the chassis ground provided by brass standoffs