Power it is provided Troubleshooting

Troubleshooting the power supply basically means isolating the supply as thecause of problems within a system and, if necessary, replacing it.

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It is seldom recommended the an inexperienced user open up a strength supply tomake repairs since of the danger high voltages present. Even whenunplugged, power supplies have the right to retain attention voltage and must be discharged(like a monitor) before service. Such inner repairs are beyond the limit ofthis book and also are particularly not recommended uneven the technician to know whathe is doing.

Many symptoms command me to suspect that the strength supply in a mechanism isfailing. This can sometimes be complicated for an inexperienced technician come seebecause, in ~ times little connection appears to exist between the symptom and thecause—the strength supply.

For example, in many instances a parity inspect error message can indicate aproblem through the power supply. This might seem strange because the same checkmessage specifically refers to memory that has failed. The connection is thatthe power supply strength the memory, and memory with inadequate power fails.

It take away some experience to recognize when this type of fail is strength relatedand not led to by the memory. One clue is the repeatability that the problem. Ifthe parity check message (or various other problem) shows up frequently and also identifiesthe exact same memory ar each time, I would certainly suspect the defective storage is theproblem. However, if the trouble seems random, or if the memory place theerror article cites as having actually failed seems random, I would suspect improperpower together the culprit. The complying with is a list of PC problems that often arerelated to the power supply:

Any power-on or system startup failure or lockups.

Spontaneous rebooting or intermittent lockups throughout normaloperation.

Intermittent parity examine or various other memory-type errors.

Hard disk and fan all at once failing come spin (no +12v).

Overheating due to fan failure.

Small brownouts cause the mechanism to reset.

Electric shocks felt on the system case or connectors.

Slight static discharges disrupt system operation.

In fact, just about any intermittent system difficulty can be caused by thepower supply. I always suspect the supply once flaky device operation is asymptom. The course, the following relatively obvious symptoms suggest right come thepower supply as a possible cause:

System is completely dead (no fan, no cursor)


Blown circuit breakers

If you doubt a power supply problem, some of the an easy measurements andthe an ext sophisticated tests outlined in this section can help you determinewhether the strength supply is in ~ fault. Since these measurements could notdetect some intermittent failures, you might have to usage a spare power supplyfor a long-term evaluation. If the symptoms and problems disappear when a knowngood preventive unit is installed, girlfriend have uncovered the resource of her problem.

Following is a straightforward flowchart to assist you zero in on typical powersupply–related problems:

Check AC strength input. Make sure the cord is firmly sit in the wallsocket and in the power supply socket. Shot a various cord.

Check DC strength connections. Make sure the motherboard and also disk drivepower connectors are firmly seated and making great contact. Check for loosescrews.

Check DC strength output. Use a digital multimeter to inspect for propervoltages. If it's below spec, change the strength supply.

Check mounted peripherals. Eliminate all boards and also drives and retest thesystem. If it works, include back in items one at a time until the device failsagain. The last item included before the fail returns is likelydefective.

Many varieties of symptoms deserve to indicate troubles with the strength supply. Becausethe power supply precise powers everything else in the system, every little thing fromdisk drive troubles to memory problems to motherboard difficulties can regularly betraced ago to the strength supply as the root cause.

Overloaded strength Supplies

A weak or poor power supply have the right to put a damper top top your principles for systemexpansion. Some systems space designed through beefy strength supplies, together if toanticipate a great deal of device add-ons and expansion components. Most desktopor tower systems are built in this manner. Some systems have inadequate powersupplies native the start, however, and also cannot adequately organization the power-hungryoptions you might want come add.

The wattage rating have the right to sometimes be an extremely misleading. Not all 300-wattsupplies are created the same. People familiar with deluxe audio equipment knowthat part watts are better than others. This walk for power supplies, too. Cheappower supplies might in truth put out the rated power, however what about noise anddistortion? few of the supplies are under-engineered to just barely satisfy theirspecifications, whereas others can greatly exceed their specifications. Manyof the cheaper supplies administer noisy or unstable power, which can causenumerous problems with the system. An additional problem through under-engineered powersupplies is the they deserve to run hot and also force the device to execute so as well. Therepeated heating and cooling of solid-state materials eventually reasons acomputer device to fail, and also engineering ethics dictate the the hot aPC's temperature, the much shorter its life. Many human being recommend instead of theoriginal supply in a device with a heavier-duty model, i m sorry solves the problem.Because power offers come in common form factors, finding a heavy-dutyreplacement for many systems is easy, as is the environment process.

Inadequate Cooling

Some the the easily accessible replacement power supplies have actually higher-capacity coolingfans 보다 the originals, which have the right to greatly expand system life and also minimizeoverheating problems—especially for the newer, hotter-running processors.If device noise is a problem, models v special fans can run more quietly thanthe traditional models. These strength supplies often use larger-diameter fans thatspin more slowly, for this reason they run an ext quietly yet move the same amount of air asthe smaller sized fans. Computer Power and Cooling specializes in heavy-duty and quietsupplies; Astec has several heavy-duty models together well.

Ventilation in a mechanism is additionally important. You need to ensure adequate airflowto cool the hotter items in the system. Countless processors this day use passiveheatsinks that need a secure stream that air come cool the chip. If the processorheatsink has its own fan, this is not much of a concern. If you have actually freeexpansion slots, girlfriend should space out the plank in your device to permitairflow in between them. Place the hottest to run boards nearest the fan or theventilation holes in the system. Make sure that enough airflow exist aroundthe tough disk drive, especially for those that spin at high prices of speed. Somehard disks can generate rather a little bit of heat throughout operation. If the difficult disksoverheat, data deserve to be lost.

Always be sure to operation your computer system with the situation cover on, especially if youhave a loaded system. Remove the cover have the right to actually cause a device tooverheat. V the sheathe off, the power supply pan no much longer draws waiting throughthe system. Instead, the pan ends up cooling the it is provided only, and the remainder ofthe mechanism must be cooled by an easy convection. Although most systems do notimmediately overheat for this reason, several of my own systems, especiallythose the are totally expanded, have overheated in ~ 15–30 minutes whenrun with the situation cover off.

In addition, be sure that any empty slot positions have the filler bracketsinstalled. If you leaving these brackets turn off after remove a card, the resultanthole in the instance disrupts the internal airflow and can cause higher internaltemperatures.

If you endure intermittent troubles that you suspect are related tooverheating, a higher-capacity replacement power supply is normally the bestcure. Particularly designed gives with additional cooling fan capacity likewise canhelp. At least one firm sells a maker called a pan card, however I to be notconvinced these are a an excellent idea. Unless the fan is positioned to draw air come orfrom the area outside the case, all it does is blow warm air around inside thesystem and administer a clues cooling result for anything the is punch on. In fact,adding fans in this manner contributes to the overall heat inside the systembecause the pan consumes power and also generates heat.

CPU-mounted fans are an exception since they space designed just for spotcooling of the CPU. Plenty of newer processors operation so lot hotter than the othercomponents in the system that a conventional, finned aluminum heatsinkcan't carry out the job. In this case, a small fan placed straight over theprocessor offers a clues cooling result that keeps the processor temperaturesdown. One drawback to these energetic processor cooling pan is that the processoroverheats instantly and also can be damaged if the pan fail. Whenever possible, tryto use the biggest passive (finned aluminum) heatsink you can find and also purchasea CPU pan from a trustworthy vendor.

Using Digital Multimeters

One straightforward test you deserve to perform on a power supply is to examine the outputvoltages. This mirrors whether a power supply is operating correctly and also whetherthe calculation voltages are within the correct tolerance range. Note that friend mustmeasure every voltages through the strength supply linked to a suitable load, whichusually way testing if the power supply is still set up in the systemand connected to the motherboard and peripheral devices.

Selecting a Meter

You need a straightforward digital multimeter (DMM) or digital volt-ohm meter (DVOM) to execute voltage and resistance checks on electronic circuits (see number 3.17). You have to use only a DMM rather of the larger needle-type multimeters since the older meters work-related by injecting 9v into the circuit as soon as measuring resistance, which damages most computer circuits.

Figure 3.17 A typical DMM.

A DMM supplies a much smaller voltage (usually 1.5v) once making resistancemeasurements, which is for sure for digital equipment. Girlfriend can obtain a great DMMwith many features from several sources. I prefer the small, pocket-size metersfor computer work due to the fact that they are straightforward to bring around.

Some features to look for in a great DMM room as follows:

Pocket size. This is self-explanatory, but small meters areavailable that have actually many, if not all, that the features of larger ones. Theelaborate features uncovered on several of the bigger meters are not really necessaryfor computer work.

Overload protection. This means that if girlfriend plug the meter right into avoltage or current beyond the meter's capacity to measure, the meterprotects itself from damage. Cheaper meters absence this protection and also can easilybe damaged through reading existing or voltage worths that are too high.

Autoranging. This way that the meter immediately selects theproper voltage or resistance range when make measurements. This is preferableto the manual range selection; however, really good meters sell bothautoranging capacity and a manual selection override.

Detachable probe leads. The leads easily can it is in damaged, andsometimes a variety of in different ways shaped probes are forced for differenttests. Cheaper meters have actually the leader permanently attached, which way youcannot quickly replace them. Look for a meter through detachable leads that pluginto the meter.

Audible continuous test. Although you have the right to use the ohm range fortesting continuous (0ohms shows continuity), a continuity test functioncauses the meter to produce a beep noise as soon as continuity exists between themeter check leads. By making use of the sound, you easily can check cable assemblies andother items for continuity. After you usage this feature, girlfriend will never want touse the ohms display for this objective again.

Automatic strength off. These meters run on batteries, and thebatteries can quickly be worn down if the meter is coincidentally left on. Goodmeters have actually an automatically shutoff that turns off the unit as soon as it senses noreadings for a predetermined period of time.

Automatic screen hold. This feature enables you to hold the laststable analysis on the display screen even ~ the analysis is taken. This isespecially useful if you room trying to job-related in a difficult-to-reach areasingle-handedly.

Minimum and also maximum trap. This feature enables the meter to trapthe lowest and highest readings in memory and hold lock for later on display, whichis especially beneficial if you have actually readings that are fluctuating too quickly tosee top top the display.

Although girlfriend can obtain a an easy pocket DMM because that as little as $20, one with allthese attributes is priced in the $100–$200 range. Radio Shack tote somenice inexpensive units, and also you deserve to purchase the luxury models fromelectronics supply houses, such together Newark or Digi-Key.

Measuring Voltage

To measure up voltages ~ above a device that is operating, you need to use a an approach called back probing ~ above the connectors (see number 3.18). You can not disconnect any kind of of the connectors when the system is running, therefore you must measure with every little thing connected. Almost all the connectors you must probe have actually openings in the back where the wires go into the connector. The meter probes space narrow enough to fit right into the connector alongside the wire and make call with the metal terminal inside. The method is called ago probing because you are probing the connector native the back. You have to use this back-probing technique to do virtually all the adhering to measurements.

Figure 3.18 earlier probing the power supply connectors.

To check a strength supply for ideal output, inspect the voltage at the Power_Goodpin (P8-1 top top AT, Baby-AT, and also LPX supplies; pin 8 top top the ATX-type connector) for+3v to +6v of power. If the measure is no within this range, the systemnever watch the Power_Good signal and therefore go not begin or run properly.In most cases, the strength supply is bad and also must it is in replaced.

Continue by measuring the voltage ranges of the pins on the motherboard anddrive strength connectors. If you space measuring voltages for testing purposes, anyreading within 10% the the specified voltage is considered acceptable, althoughmost manufacturers that high-quality power offers specify a tighter 5%tolerance. Because that ATX power supplies, the specification requires that voltages mustbe in ~ 5% the the rating, other than for the 3.3v current, which have to be within4%. The following table reflects the voltage varieties within this tolerances.

Loose Tolerance

Tight Tolerance

Desired Voltage

Min. (-10%)

Max. (+8%)

Min. (-5%)

Max. (+5%)
















The Power_Good signal has actually tolerances that are various fromthe various other voltages, although the is nominally +5v in many systems. The triggerpoint for Power_Good is around +2.4v, yet most systems need the signal voltageto be within the tolerances listed here:




Power_Good (+5V)



Replace the strength supply if the voltages you measure room out ofthese ranges. Again, the is worth noting that any and also all power supply test andmeasurements need to be made with the power supply properly loaded, i m sorry usuallymeans it need to be set up in a system and also the mechanism must it is in running.

Specialized test Equipment

You deserve to use several varieties of dedicated test equipment to test power suppliesmore effectively. Due to the fact that the strength supply is one of the many failure-proneitems in pcs today, girlfriend should have these dedicated items if you service manyPC systems.

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Digital Infrared Thermometer

One of the greatest additions to my toolbox is a digital infraredthermometer. They additionally are dubbed noncontact thermometers due to the fact that theymeasure through sensing infrared power without having actually to touch the item lock arereading. This permits me to make prompt spot checks of the temperature the achip, a board, or the system chassis. Lock are available from suppliers such asRaytek (http://www.raytek.com)for under $100. To use these handheld items, you point at an object and thenpull the trigger. Within seconds, the display shows a temperature readout. Thesedevices are invaluable in checking to for sure your mechanism is adequatelycooled.