Back To Contents Page
Maintaining the System
Proper use of preventive maintenance
procedures can keep the system in top operating condition and minimize the need for
costly, time-consuming service procedures. This section contains maintenance procedures
that you should perform regularly.
Everyone inadvertently deletes files at
one time or another. Also, hard-disk drives can fail after extended use, so it is not a
question of whether you will eventually lose data, but when. To avoid such loss of data,
you should regularly make backup copies of all hard-disk drive files. Frequent, regular
backups are a must for anyone using a hard-disk drive.
The
frequency with which backups should be made depends on the amount of storage space on a
hard-disk drive and the volatility of the data contained on the drive. Heavily used
systems require more frequent backups than systems in which files are seldom changed.
Dell recommends that you back up the
hard-disk drive at least once a week, with a daily backup of those files known to have
been changed. Following these guidelines ensures the loss of no more than a day's work in
the event of a hard-disk drive failure or if you inadvertently delete one or more
important files.
As further insurance against data losses,
you should keep duplicate copies of the weekly and monthly backups at an off-site
location. Doing this ensures that you lose no more than a week's work, even if one of the
on-site backups becomes corrupted.
Tape drives are fast, convenient, and
reliable devices that can back up data at rates of up to 1.5 megabytes per second (MB/sec)
(sustained, without data compression) and can often run unattended. Dell offers tape
drives with storage capacities in the range of 20 to 70 gigabytes (GB) (when available)
per tape cartridge and recommends these drives and their associated backup software for
use as system backup devices.
As a last resort, you can back up a
hard-disk drive's contents on diskettes, a method that is both time-consuming and prone to
human error. Also, backing up a full 4-GB hard-disk drive requires approximately 277
diskettes (when using 1.44-MB diskettes), 334 diskettes (when using 1.2-MB diskettes), or
139 diskettes (when using 2.88-MB diskettes). Therefore, if it is absolutely necessary to
use diskettes as backup devices, any unwanted hard-disk drive files should be deleted
before a backup procedure is started.
Some hard-disk drive failures are
recoverable. In these cases you may be able to recover all lost data if the proper utility
software is available. Even losses such as accidentally deleted files or accidental
reformatting of a hard-disk drive can be reversed with these utilities.
If the system is running MS-DOS, many
apparent data loss problems are due to corruption or erasure of the hard-disk drive's
master boot record (MBR), MS-DOS boot sector, or file allocation table (FAT). That is,
accidental deletion of files or accidental reformatting of the hard-disk drive alters the
MS-DOS boot sector, the FAT, and the root directory.
However, such accidents do not actually
erase the contents of the hard-disk drive files until new data is written to the sectors
containing these files. With software such as the Norton Utilities, Mace Utilities, or
PC-Tools Deluxe, the data stored in these areas can often be restored, meaning that you
can recover most, if not all, of the data.
Unlike using the format command on a
hard-disk drive, using format on a diskette completely erases all the data on the diskette
unless you use the diskette format program included in the Mace Utilities.
For a complete description of data
recovery procedures and the software needed to perform them, see The Paul Mace Guide to
Data Recovery, published by Brady.
An exhaust fan in the power supply cools
the power supply and system by drawing air in through various openings in the system and
blowing it out the back. However, the fan also draws dust and other particles into the
system, causing contaminant buildup, which results in an increase in the system's internal
temperature and interferes with the operation of various system components.
To avoid these conditions, Dell
recommends keeping your work environment clean to reduce the amount of dust and dirt
around the system, thereby reducing the amount of contaminants drawn into the system by
the power supply fan. In particular, you should keep the exterior of your system and
monitor clean, and you should use a commercially available diskette-drive head-cleaning
kit to remove contaminants inside your diskette drives.
Dell recommends that you use the
following tools and accessories when you clean the system:
- A wrist grounding strap -- The proper use of a wrist
grounding strap reduces the effect of electrostatic discharge (ESD), which can damage
certain system components. To use a wrist grounding strap, place the strap around your
wrist and attach the other end of the strap to an unpainted metal surface in the chassis,
such as the power supply bracket, that is connected to chassis ground.
- A liquid dishwashing detergent -- Use a mixture of one part
liquid dishwashing detergent and three parts water to clean the exterior of the system,
monitor, and keyboard. You can also add fabric softener to produce an antistatic solution
that prevents dust from being attracted to the monitor screen.
- A soft, lint-free cleaning cloth -- Moisten the cleaning
cloth with the dishwashing detergent solution to clean the exterior of the system.
- A nonabrasive diskette-drive head-cleaning kit -- Dell recommends that you use a kit that contains pretreated
diskettes in individually sealed packages. These kits ensure that the cleaning solution is
applied evenly over the entire diskette-drive head surface, and they prevent contamination
of the heads by exposure to foreign substances.
- A small vacuum cleaner with a brush attachment -- Use the
vacuum cleaner to remove dust and dirt from the exterior of the system and keyboard.
A conventional monitor or keyboard cover
minimizes the accumulation of dust and other debris inside the monitor and keyboard when
they are not in use. Also, commercially available keyboard membrane covers make it
possible to use the keyboard while providing protection against foreign particles.
However, regardless of any protective
covers, the monitor and keyboard must be cleaned occasionally. To clean the exterior of
the system, monitor, and keyboard, follow these steps:
Turn off the system, monitor, and any other attached
peripherals, and disconnect them from their power sources.
Use a vacuum cleaner to remove any dust from the slots and
holes on the system and between the keys on the keyboard.
Moisten a soft cleaning cloth with a solution of three parts
water and one part liquid dishwashing detergent.
Do not soak the cloth in the solution; you must not let the
solution drip inside the system or keyboard.
Use the moistened cloth to wipe the system cover, the keyboard,
and the exterior of the monitor, including the screen.
You can clean the heads of your diskette
drives by using a commercially available diskette-drive head-cleaning kit. These kits
include diskettes pretreated with a chemical solution to nonabrasively remove contaminants
that accumulate on the drive heads during normal operation.
If the kit does not contain instructions,
insert one of the pretreated diskettes into a diskette drive and turn on the system. After
20 or 30 seconds, remove the diskette from the drive. Repeat this procedure for each
diskette drive in the system.
 |
CAUTION:
Do not attempt to clean drive heads with a swab. You
may accidentally misalign the heads, rendering the drive inoperable. |
This section discusses various
environmental factors that can adversely affect system performance and longevity.
Temperature extremes can cause a variety
of problems, including premature aging and failure of chips or mechanical failure of
devices. Extreme temperature fluctuations can cause chips to become loose in their sockets
and can cause expansion and contraction of disk drive platters, resulting in read or write
data errors. When you perform a low-level format operation on a hard-disk drive, it is
important to ensure that the drive's surrounding temperature is at or near the temperature
at which the drive will be operated. Failure to do so can result in relocation of the
tracks on the disk platters.
To minimize the negative effects of
temperature on system performance, follow these guidelines:
- Ensure that the system is operated in an environment no colder than
10 Celsius (C) (50 Fahrenheit [F]) or hotter than 35C (95F).
- Ensure that the system has adequate ventilation. Do not place it within a
closed-in wall unit or on top of cloth material, which can act as insulation. Do not place
it where it will receive direct sunlight, particularly in the afternoon. Do not place it
next to a heat source of any kind, including heating vents during winter.
Adequate ventilation is particularly
important at high altitudes. System performance may not be optimum when the system is
operating at high temperatures as well as high altitudes.
- Make sure that all slots and openings on the system remain unobstructed,
especially the fan vent on the back of the system.
- Clean the system at regular intervals to avoid any buildup of dust and
debris, which can cause a system to overheat.
- If the system has been exposed to abnormally cold temperatures, allow a
two-hour warm-up period to bring it up to normal operating temperature before turning it
on. Failure to do so may cause damage to internal components, particularly the hard-disk
drive.
- If intermittent system failures are noticed, try reseating any socketed
chips, which might have become loose due to temperature fluctuations.
High-humidity conditions can cause
moisture migration and penetration into the system. This moisture can cause corrosion of
internal components and degradation of properties such as electrical resistance, thermal
conductivity, physical strength, and size. Extreme moisture buildup inside the system can
result in electrical shorts, which can cause serious damage to the system.
Each Dell™ system is rated to operate at 8
to 80 percent relative humidity, with a humidity gradation of 10 percent per hour. In
storage, a Dell system can withstand from 5 to 95 percent relative humidity.
Buildings in which climate is controlled
by air-conditioning in the warmer months and by heat during the colder months usually
maintain an acceptable level of humidity for system equipment. However, if a system is
located in an unusually humid location, a dehumidifier can be used to maintain the
humidity within an acceptable range.
Operating a system at high altitude (low
pressure) reduces the efficiency of forced and convection cooling and can result in
electrical problems related to arcing and corona effects. This condition can also cause
sealed components with internal pressure, such as electrolytic capacitors, to fail or
perform at reduced efficiency.
Each Dell system is rated to operate at
altitudes from -16 to 3048 meters (m) (-50 to 10,000 feet [ft]) and can be stored at
altitudes of -16 to 10,600 m (-50 to 35,000 ft).
A clean operating environment can greatly
reduce the negative effects of dust and other particles, which act as insulators and
interfere with the operation of a system's mechanical components. Also, in addition to
regular cleaning, you should follow these guidelines to deter contamination of the system
equipment:
- Do not permit smoking anywhere near the system.
- Do not permit food or drink near the system.
- Use dust covers when the system is not in use.
- Keep all diskettes in a closed diskette box when not in use.
- Close windows and outside doors to keep out airborne particles.
The oil from a person's fingers or
prolonged exposure to high temperature or humidity can corrode the gold-plated edge
connectors and pin connectors on various devices in the system. This corrosion on system
connectors is a gradual process that can eventually lead to intermittent failures of
electrical circuits.
To prevent corrosion, you should avoid
touching contacts on boards and cards. Protecting the system from corrosive elements is
especially important in moist and salty environments, which tend to promote corrosion.
Also, as a further deterrent to corrosion, the system should not be used in extreme
temperatures, as explained in Temperature.
ESD results from the buildup of static electricity on the human
body and certain other objects. This static electricity is often produced by simple
movements such as walking across a carpet. ESD is a discharge of a static electrical
charge, that occurs when a person whose body contains such a charge touches a component in
the system. This static discharge can cause components, especially chips, to fail. ESD is
a problem particularly in dry environments where the relative humidity is below 50
percent. To reduce the effects of ESD, you should observe the following guidelines:
- When working inside the system, wear a wrist grounding strap. If a wrist
grounding strap is unavailable, touch an unpainted metal surface on the chassis
periodically to neutralize any static charge.
- If at all possible, stand on a concrete floor while working inside the
system.
- Use an antistatic floor mat when working inside the system.
- If it is necessary to work in a carpeted area, spray the carpet with an
antistatic spray and allow it to dry before beginning to work inside the system.
- Keep components in their antistatic packaging until they are installed.
- Avoid wearing clothing made of wool or synthetic materials.
Electromagnetic interference (EMI) and
radio frequency interference (RFI) from a system can adversely affect devices such as
radio and television (TV) receivers operating near the system. Radio frequencies emanating
from a system can also interfere with cordless and low-power telephones. Conversely, RFI
from high-power telephones can cause spurious characters to appear on the system's monitor
screen.
RFI is defined as any EMI with a
frequency above 10 kilohertz (kHz). This type of interference can travel from the system
to other devices through the alternating current (AC) power cable and power source or
through the air like transmitted radio waves. The Federal Communications Commission (FCC)
publishes specific regulations to limit the amount of EMI and RFI emitted by computing
equipment. Each Dell system meets these FCC regulations.
To reduce the possibility of EMI and RFI,
follow these guidelines:
- Operate the system only with the system cover installed.
- Ensure that all expansion slots are covered either by a card-mounting
bracket or by a metal filler bracket and that all drive bays have a drive and/or a metal
insert installed. These brackets and metal inserts are available from Dell.
- Ensure that the screws on all peripheral cable connectors are securely
fastened to their corresponding connectors on the back of the system.
- Always use shielded cables with metal connector shells for attaching
peripherals to the system.
To prevent the possibility of RFI from a
system affecting TV reception, follow these guidelines:
- Keep any TV set at least 6 ft away from the system.
- Use cable TV when possible.
- Use a directional outdoor TV antenna.
- Attach line filters to the TV set.
- Use 75-ohm coaxial cable for the TV set rather than twin-lead antenna
wire.
- If interference occurs, rotate the system or the TV set 90 degrees.
Because they store data magnetically,
diskettes and hard-disk drives are extremely susceptible to the effects of magnetism.
Diskettes should never be stored near magnetic sources such as the following:
- Monitors
- TV sets
- Printers
- Telephones with real bells
- Fluorescent lights
Excessive shock can damage the function,
external appearance, and physical structure of a system. Each Dell system has been
designed to operate properly even after withstanding a minimum of six consecutively
executed shock pulses in the positive and negative x, y, and z axes (one pulse on each
side of the system). Each shock pulse can measure up to 50 gravities (G) for up to
2 milliseconds (ms). In storage, the system can withstand shock pulses of 92 G for 2
ms.
Excessive vibration can cause the same
problems as mentioned earlier for shock, as well as cause components to become loose in
their sockets or connectors. Systems can be subject to significant vibration when being
transported by vehicle or when operated in an environment with machinery that causes
vibration.
Each Dell system, when operating, is
designed to withstand 0.25 G (half-sine wave) at a sweep of 3 to 200 hertz (Hz) for
15 minutes. In storage, the system can withstand 0.5 G at 3 to 200 Hz for 15 minutes.
Systems are especially sensitive to
variations in voltage supplied by the AC power source. Over-voltage, undervoltage, and
transients (or spikes) can erase data from memory or even cause components to fail. To
protect against these types of problems, power cables should always be properly grounded
and one or both of the following methods should be used:
- Use one of the power protection devices described in the following
section, "Power Protection Devices."
- Place the system on a dedicated power circuit (rather than sharing a
circuit with other heavy electrical equipment). In general, do not allow the system to
share a circuit with any of the following:
- Copier machines
- Air conditioners
- Vacuum cleaners
- Space heaters
- Power tools
- Teletype machines
- Adding machines
- Laser printers
- Facsimile machines
- Any other motorized equipment
Besides these appliances, the greatest
threat to a system's supply of power are surges or blackouts caused by electrical storms.
Whenever possible, turn off the system and any peripherals and unplug them from their
power sources during thunderstorms.
If a blackout occurs--even a temporary
one--while the system is turned on, turn off the system immediately and disconnect it from
its power source. Leaving the system on may cause problems when the power is restored; all
other appliances left on in the area can create large voltage spikes that can damage the
system.
A number of devices are available that
protect against power problems, such as power surges, transients, and power failures. The
following subsections describe some of these devices.
Surge protectors are available in a
variety of types and usually provide a level of protection commensurate with the cost of
the device. Surge protectors prevent voltage spikes, such as those caused during an
electrical storm, from entering a system through the AC power source. Surge protectors,
however, do not offer protection against brownouts, which occur when the voltage drops
more than 20 percent below the normal AC line voltage level.
Line conditioners go beyond the
overvoltage protection of surge protectors. Line conditioners keep a system's AC power
source voltage at a fairly constant level and, therefore, can handle brownouts. Because of
this added protection, line conditioners cost more than surge protectors--up to several
hundred dollars. However, these devices cannot protect against a complete loss of power.
Uninterruptible power supply (UPS)
systems offer the most complete protection against variations in power because they use
battery power to keep the system running when AC power is lost. The battery is charged by
the AC power while it is available, so once AC power is lost, the battery can provide
power to the system for a limited amount of time--from 15 minutes to an hour or
so--depending on the UPS system.
UPS systems range in price from a few
hundred dollars to several thousand dollars, with the more expensive units allowing you to
run larger systems for a longer period of time when AC power is lost. UPS systems that
provide only 5 minutes of battery power let you conduct an orderly shutdown of the system,
but are not intended to provide continued operation. Surge protectors should be used with
all UPS systems, and the UPS system should be Underwriters Laboratories (UL)
safety-approved.
Back To Contents Page
