Rosewill Computer Case 422 Informacje Techniczne Pobierz pdf (Strona 71)

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Chapter 4 • Disassembly and Power

• Is a surge strip used? If so, check to see if the surge strip is powered on, then try a dif-

ferent outlet in the surge strip, or replace the surge strip.

• Is the computer’s power cord okay? Verify that the power cord plugs snugly into the

outlet and into the back of the computer. Swap the power cord to verify that it is func-

tioning.

• Is the front panel power button stuck?

• Are the voltages going to the motherboard at the proper levels? If they are low, some-

thing may be overloading the power supply. Disconnect the power cable to one device

and recheck the voltages. Replace the power cable to the device. Remove the power

cable from another device and recheck the motherboard voltages. Continue doing this

until the power cord for each device has been disconnected and the motherboard volt-

ages have been checked. A single device can short out the power supply and cause the

system to malfunction. Replace any device that draws down the power supply’s output

voltage and draws too much current. If none of the devices is the cause of the problem,

replace the power supply. If replacing the power supply does not solve the problem,

replace the motherboard.

If a computer does not boot properly, but it does boot when you press c + a + D,

the power good signal is likely the problem. Some motherboards are more sensitive to the

power good signal than others. For example, say that a motherboard has been replaced and the

system does not boot. At first glance, this may appear

to be a bad replacement board, but the problem could

be caused by a power supply failing to output a consis-

tent power good signal.

Sometimes, none of these troubleshooting actions

work. A grounding problem might be the issue. Build

the computer outside the computer case, on an anti-

static mat, if possible. Start with only the power sup-

ply, motherboard, and speaker connected. Even though

it will normally produce a POST audio error, verify

that the power supply fan will turn. Most power sup-

plies issue a click before the audio POST beeps. Next,

verify the voltages from the power supply. If the fan

turns and the voltages are correct, power down the

machine and add a video adapter and monitor to the system. If the machine does not work, put

the video adapter in a different expansion slot and try again. If placing the video adapter in a

different expansion slot does not work, swap out the video adapter.

If the video adapter works, continue adding devices one by one and checking the voltages.

Just as any one device can cause the system not to operate properly, so can any one adapter. If

one particular adapter causes the system to malfunction, try a different expansion slot before

trying a different adapter.

If the expansion slot proves to be a problem, check the slot for foreign objects. If none are

found but the problem still occurs, place a note on the expansion slot so that no one will use it.

Adverse Power Conditions

There are two adverse AC power conditions that can damage or adversely affect a computer:

overvoltage and undervoltage. Overvoltage occurs when the output voltage from the wall

outlet (the AC voltage) is over the rated amount. Normally, the output of a wall outlet is 110

to 130 volts AC. When the voltage rises above 130 volts, an overvoltage condition exists. The

power supply takes the AC voltage and converts it to DC. An overvoltage condition is harmful

to the components because too much DC voltage destroys electronic circuits. An overvoltage

condition can be a surge or a spike.

Check the power good (sometimes

called power OK) signal

Check the power supply documentation to see

if the power supply outputs a power good signal

(rather than the normal +5 volts). Turn on the

computer. Check the power good signal going

into the motherboard power connector. Do this

before replacing the motherboard. A power supply

with a power good signal below +3V needs to be

replaced.

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