One issue you must be aware of is electrostatic discharge (ESD) protection. Another is recording the configuration of the system with regard to the physical aspects of the system (such as jumper or switch settings and cable orientations) and the logical configuration of the system (especially in terms of elements such as CMOS settings).
When you are working on the internal components of a computer, you must take the necessary precautions to prevent accidental static discharges to the components. At any time, your body can hold a large static voltage charge that can easily damage components of your system.
Before I ever put my hands into an open system, I first touch a grounded portion of the chassis, such as the power supply case. This action serves to equalize the electrical charges the device and my body might be carrying. Be sure the power supply is unplugged during all phases of the assembly process.
Some will claim that you should leave the system plugged in to provide an earth ground through the power cord and outlet, but that is unnecessary. If you leave the system plugged in, you open yourself up to other problems, such as accidentally turning it on or leaving it on when installing a board or device, which can damage the motherboard or other devices.
High-end workbenches at repair facilities have the entire bench grounded, so it's not as big of a problem; however, you need something to be a good ground source to prevent a current from building up in you. A more sophisticated way to equalize the charges between you and any of the system components is to use an ESD protection kit.
These kits consist of a wrist strap and mat, with ground wires for attachment to the system chassis. When you are going to work on a system, you place the mat next to or partially below the system unit. Next, you clip the ground wire to both the mat and the system's chassis, tying the grounds together.
You then put on the wrist strap and attach that wire to a ground. Because the mat and system chassis are already wired together, you can attach the wrist-strap wire to the system chassis or to the mat. If you are using a wrist strap without a mat, clip the wrist-strap wire to the system chassis.
When clipping these wires to the chassis, be sure to use an area that is free of paint so a good ground contact can be achieved. This setup ensures that any electrical charges are carried equally by you and any of the components in the system, preventing the sudden flow of static electricity that can damage the circuits.
As you install or remove disk drives; adapter cards; and especially delicate items such as the entire motherboard, SIMMs, or processors, you should place these components on the static mat. Sometimes people put the system unit on top of the mat, but the unit should be alongside the mat so you have room to lay out all the components as you work with them.
If you are going to remove the motherboard from a system, be sure you leave enough room for it on the mat. If you do not have such a mat, place the removed circuits and devices on a clean desk or table. Always pick up a loose adapter card by the metal bracket used to secure the card to the system.
This bracket is tied into the ground circuitry of the card, so by touching the bracket first, you prevent a discharge from damaging the components of the card. If the circuit board has no metal bracket (a motherboard, for example), handle the board carefully by the edges, and try not to touch any of the connectors or components.
If you don't have proper ESD equipment such as a wrist strap or mat, be sure to periodically touch the chassis while working inside the system to equalize any charge you might have built up.
Recording Physical Configuration
While you are assembling a system, you should record all the physical settings and configurations of each component, including jumper and switch settings, cable orientations and placement, ground wire locations, and even adapter board placement. Keep a notebook handy for recording these items, and write down all the settings.
It is especially important to record all the jumper and switch settings on the motherboard, as well as those on any card you install in the system (cards seldom use jumpers or switches today, but some motherboards still do). If you accidentally disturb these jumpers or switches, you will know how they were originally set.
This knowledge is very important if you do not have all the documentation for the system handy. Even if you do, undocumented jumpers and switches often do not appear in the manuals but must be set a certain way for the item to function. Also, record all cable orientations.
Most name-brand systems use cables and connectors that are keyed so that they can't be plugged in backward, but some generic PCs do not have this added feature. You should mark or record what each cable was plugged into and its proper orientation. Ribbon cables usually have an odd-colored (red, green, blue, or black) wire at one end that indicates pin 1.
There might also be a mark on the connector, such as a triangle or even the number 1. The devices the cables are plugged into are also marked in some way to indicate the orientation of pin 1. Often, a dot appears next to the pin 1 side of the connector, or a 1 or other mark might appear.
Although cable orientation and placement seem to be very simple, we rarely get through the entire course of my PC troubleshooting seminars without at least one group of people having cable-connection problems. Fortunately, in most cases (except power cables), plugging any of the ribbon cables inside the system backward doesn't cause any permanent damage.
Power and battery connections on pre-ATX systems are exceptions; plugging them in backward in most cases causes damage. In fact, plugging the motherboard power connectors in backward or in the wrong plug location on these older systems puts 12V where only 5V should be—a situation that can cause components of the board to violently explode.
I know of several people who have facial scars caused by shrapnel from components that exploded because of improper power supply connections! As a precaution, I always turn my face away from the system when I power it on for the first time. If you are using an ATX board and power supply, there is little chance of this happening because of the superior type of power connector used.
Plugging in the CMOS battery backward can damage the CMOS chip, which usually is soldered into the motherboard; in such a case, the motherboard must be replaced. Finally, you should record miscellaneous items such as the placement of any ground wires, adapter cards, and anything else that you might have difficulty remembering later.
Some configurations and setups might be particular about the slots in which the adapter cards are located, so you should put everything back exactly the way it was originally.