May 18, 2011, 11:29 p.m.
posted by shadow
Time Shaver If you have built or reassembled many PCs, you are probably reasonably prepared for the A+ Hardware Technology exam. For review, then, write down the steps that you use to build or reassemble a PC, along with any safeguards and safety and performance checks that you use along the way. Then jump to the last section of this chapter — “Testing the Results” — and review it for common device failure modes. You can expect to see several common device failure modes on the exam.
For the exam, make sure that you know the general sequence of assembly and the relationship of the major FRMs to each other. Questions either assume knowledge or directly ask how FRMs are installed and ask how associated cables and wires are attached. You won’t see questions that directly ask how a PC is assembled.
FRMs are reassembled in essentially the reverse order that they were removed. Assuming that the power supply wasn’t removed from the system case (a wise decision), the motherboard (with its memory reinstalled) goes in first, then the hard drives, the adapter cards, and finally, the case parts. If the power supply was removed, it must be reinstalled first, with the other components following in their natural sequence.
You need more tools to reassemble the PC than to disassemble it: an ESD grounding strap, a Phillips screwdriver, a slotted screwdriver, a pair of needle-nosed pliers, and a small flashlight. Mature eyes may also want a small magnifying glass. The most important tool, however, is patience. Take your time. If something isn’t right, and no smoke was involved in reaching that decision, take the computer apart and do it again.
Shocking Information Protecting the PC and its FRMs from ESD damage is as important when reassembling the system as when taking it apart. Use your grounding straps, or take other appropriate precautions. Together, you and ESD are the most threatening element to a PC. Whatever you can do to reduce this threat gives additional life to the PC. Makes you feel kind of powerful, doesn’t it?
Instant Answer The greatest threat of ESD damage to the PC is working on the PC with its case open without proper ESD protection in place.
It’s easy to reinstall the power supply. Just line up the fan with its hole in the case, match the power supply to the screw holes, and then insert the screws. The only required safeguard take is to make sure that the power supply’s cables are not trapped under the case or along its sides.
This may sound obvious, but when you install the power supply, it shouldn’t be plugged into an AC power source. After you install the power supply, plug it in and operate it briefly to test the fan — and the fan only. If the fan turns, all is well. If the fan doesn’t operate, determine whether the power supply’s voltage selector is set correctly and whether the power cord is seated tightly.
Warning Do not use a screwdriver, your finger, or anything else to turn the fan blade. If all is well, and the fan still doesn’t turn, replace the power supply.
As you reassemble the PC, pay your greatest attention to the motherboard and its cables and connections. Putting a floppy disk drive in backward is a mistake that’s easily corrected and normally does no harm, but some of the connectors on the motherboard can do extreme damage to the motherboard and other components if they are installed incorrectly. So take care as you work.
Shocking Information Do not begin to reassemble the PC without first putting on your ESD ground strap and connecting it to the PC case or ground mat. Do you get the impression that I think this is important?
If you are installing a new motherboard in an existing system case, you must verify several conditions, including the fact that the motherboard is compatible with the form factor of the case and power supply, and that the devices in the PC are compatible with the motherboard and its BIOS and chipset. Most of this information is available in the motherboard’s documentation or on the manufacturer’s Web site. Look up this information before you try to install the new motherboard; it saves you and your customer money in the end.
Lab 15-4 shows you how to reinstall the motherboard.
Orient the motherboard so that its spacers (also called standoffs) are aligned with the slots in the bottom of the case.
Laterally slide the motherboard toward the power supply until the standoffs are firmly snug in their slots.
Reinsert the mounting screws to anchor the motherboard in place.
Most motherboards are attached to the case with screws. Some new case designs allow the motherboard to be attached to a hinged plate with only the spacers locking it into place. If screws are used, use either Teflon or plastic washers under the mounting screws when attaching the motherboard to the system case; this prevents the screw heads from contacting circuitry on the motherboard. Be sure that the electronic contacts and cut pins on the motherboard are not in contact with the metal case lining. Contact will give you trouble — if it doesn’t short out the motherboard. Look under the motherboard to verify that it is not touching the case.
To complete the installation, reattach the speaker, keylock, and battery connectors.
If the motherboard has a separate battery supply, keep it connected to the motherboard throughout this process. If it was removed, or if the system battery was removed, you must set the system’s configuration (by using the CMOS setup utility) the first time that you boot the PC.
The procedure and the level of caution that you should use to connect the motherboard to the power supply depends on its form factor. You use a different process and different connectors for AT form-factor motherboards than for ATX or later motherboards. The differences are as follows:
AT motherboards: The two six-wire power supply connectors for AT form-factor motherboards should be labeled as P8 and P9. These two connectors are installed side by side into a 12-pin connector on the motherboard. It is possible to reverse the positions of these two connectors. If you reverse them, you will need a new motherboard. However, because you labeled them and drew a diagram when disassembling the PC, you know exactly which goes on the right and which goes on the left of the connector.
Remember: The four black wires (two on each plug) must be aligned together in the middle.
Warning If you forget to connect the motherboard power connectors (P8 and P9), when you turn on the power, the power supply may explode — or at the least make loud, ugly noises. So don’t forget to install these plugs!
ATX (and later) motherboards: You can easily distinguish the power connector on these form-factor motherboards by its unique size and shape, and installation is easy because of its connector key. The connector has 2 rows of 10 pins in a rectangular shape. You should have it labeled and included on your diagram.
See Chapter 3 for more information on motherboard form factors.
If the PC has a power cable for the front panel, which means that it has a main power switch on the front of the PC, unplug the PC for the duration of this operation. The front-panel cable that comes from the power supply carries 110V AC power that is passed straight from the AC wall socket. This isn’t something with which you should take chances. Even if you diagrammed the front panel power switch connector during disassembly, check the power supply’s documentation, if available, for the wire color scheme.
The power switch on the front panel closes a circuit that allows the AC power to flow to the power supply. To allow this flow, the power switch has both hot (live) and return (to the power supply) leads.
Some technicians prefer to install the hard drives before the adapter cards, and others like to do the reverse. Whichever you do first, the same rules apply, just in a different order. Follow your diagram, and reinstall the adapter cards and drives, keeping the cables and cards spaced evenly to allow good airflow. Place the hard drive as far from the power supply as possible to allow maximum air circulation inside the cabinet.
You may want to take this opportunity to clean the edge connectors of the adapter cards with an edge connector cleaner and protector. You can find these products at most computer supply stores.
Time Shaver Expect questions on how cables are connected to adapter cards and the power supply. For the A+ Hardware Technology exam, it doesn’t matter which you install first (drives or adapter cards).
A common installation error is forgetting to attach the power cables to hard drives. This error can be a result of the full attention that is required to align the drive in the bay correctly, making sure that round-headed screws anchor the drive in the bay and that the data connection (the dreaded ribbon cable) is attached correctly. If you don’t attach the power connector to the drive, a POST (Power-On Self-Test) boot disk failure usually results.
In general, ribbon cables connect the same way on either end. However, this versatility can get you into trouble. You must connect the cable so that the wires connect to their counterparts on both connections. To help you with this connection, the wire representing pin 1 on the cable and connector is usually marked with a red or dark blue stripe along the edge of the cable.
You may have two or more ribbon cables to reinstall. The cable for the floppy disk drive is slightly different from the cable for the hard drive or other drives. Be sure to reattach the correct cable to the correct device, although this shouldn’t present a big problem, because usually they won’t attach to the wrong device anyway.
Excuse the veiled sports metaphor here, but an easy way to remember the orientation of a ribbon cable is the phrase “Big Red is Number 1.” If you forget this phrase, ask anyone from Nebraska who’s Number 1. You’ll be reminded that the red-stripe edge of the ribbon cable aligns to pin number 1. For ribbon cables with a dark blue edge, you’ll have to find somebody from Michigan or Duke to help you.
Finding pin 1 on the circuit board is the next step to completing the match. How do you tell which end of the connector is pin 1? A small numeral 1 should be printed next to or above the end of the connector that is pin 1. A magnifying glass may be handy in this situation, along with a flashlight. If you can’t find the printed number, examine the solder pads on the back of the circuit board where the connector is attached. Pin 1 has a square solder pad. These general rules are not universally applied, though, which is why your diagrams are so important.
Remember Watch out for the following common ribbon cable connection errors:
The connector is reversed. This can do major damage, so chant the mantra “Big Red/Blue is Number 1” as you connect ribbon cables.
The connector is attached to only one row — it’s easy to do this, given the size of the connector and the pins. If you catch this error before the power is turned on, no damage should result.
The connector is shifted to the left or right, missing a pair of pins — this is also easily done and just as dangerous.
Reattach the case top. You may want to put the top in place, but leave the screws out until after you’ve had a chance to test the results. When reattaching the case top, don’t snag or trap cables. Cables can get damaged by little nicks or breaks. They may also pull out of connectors if dragged or dinged by the case top. If the case lid doesn’t slide freely into place, investigate the problem.
Tip When reassembling the case parts, ensure that they line up properly and that the seams fit the same as before you disassembled the case. The case is an integral part of the cooling system of the PC. Misaligned case parts could create air leaks that could cause the difference between a great-running system and one with overheating processors and memory.