Power supply Troubleshooting

Troubleshooting the power supply basically method isolating the supply together thecause of troubles within a mechanism and, if necessary, instead of it.

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It is hardly ever recommended the an inexperienced user open a power supply tomake repairs due to the fact that of the dangerous high voltages present. Also whenunplugged, power supplies deserve to retain attention voltage and also must be discharged(like a monitor) before service. Such interior repairs are beyond the limit ofthis book and also are especially not recommended uneven the technician knows whathe is doing.

Many symptoms lead me to suspect that the strength supply in a system isfailing. This can sometimes be difficult for one inexperienced technician come seebecause, at times little connection appears to exist between the symptom and thecause—the power supply.

For example, in many situations a parity check error message have the right to indicate aproblem with the power supply. This can seem strange due to the fact that the same checkmessage specifically describes memory that has failed. The link is thatthe strength supply powers the memory, and memory with insufficient power fails.

It take away some suffer to recognize when this form of failure is power relatedand not led to by the memory. One proviso is the repeatability of the problem. Ifthe parity inspect message (or various other problem) appears frequently and identifiesthe very same memory place each time, I would suspect that defective memory is theproblem. However, if the difficulty seems random, or if the memory location theerror message cites as having failed seems random, I would suspect improperpower together the culprit. The following is a perform of PC problems that often arerelated come the strength supply:

Any power-on or mechanism startup failure or lockups.

Spontaneous rebooting or intermittent lockups during normaloperation.

Intermittent parity examine or other memory-type errors.

Hard disk and fan concurrently failing come spin (no +12v).

Overheating because of fan failure.

Small brownouts cause the system to reset.

Electric shocks felt on the system instance or connectors.

Slight revolution discharges disrupt device operation.

In fact, just around any intermittent system problem can be led to by thepower supply. I constantly suspect the supply when flaky mechanism operation is asymptom. Of course, the following reasonably obvious symptoms suggest right to thepower supply as a feasible cause:

System is totally dead (no fan, no cursor)


Blown circuit breakers

If you doubt a strength supply problem, several of the straightforward measurements andthe much more sophisticated exam outlined in this ar can help you determinewhether the power supply is in ~ fault. Since these measurements might notdetect some intermittent failures, you might have to use a spare power supplyfor a long-term evaluation. If the symptoms and also problems disappear when a knowngood spare unit is installed, girlfriend have found the source of your problem.

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

Check AC power input. Make sure the cord is firmly seated in the wallsocket and in the power supply socket. Try a different cord.

Check DC strength connections. Make certain the motherboard and disk drivepower connectors room firmly seated and making great contact. Check for loosescrews.

Check DC power output. Usage a digital multimeter to check for propervoltages. If it's listed below spec, change the power supply.

Check set up peripherals. Eliminate all boards and also drives and retest thesystem. If the works, include back in items one in ~ a time until the mechanism failsagain. The last item included before the failure returns is likelydefective.

Many varieties of symptoms deserve to indicate problems with the strength supply. Becausethe power supply precise powers everything else in the system, everything fromdisk drive difficulties to memory troubles to motherboard troubles can often betraced back to the power supply as the source cause.

Overloaded power Supplies

A weak or poor power supply can put a damper on your principles for systemexpansion. Some systems are designed v beefy strength supplies, as if toanticipate a great deal of device add-ons and expansion components. Many desktopor tower equipment are constructed in this manner. Some systems have inadequate powersupplies from the start, however, and cannot adequately company the power-hungryoptions you could want come add.

The wattage rating can sometimes be very misleading. Not all 300-wattsupplies are created the same. People familiar with luxury audio systems knowthat some watts are far better than others. This walk for power supplies, too. Cheappower supplies could in reality put out the rated power, however what around noise anddistortion? several of the supplies are under-engineered to just barely satisfy theirspecifications, vice versa, others could greatly exceed their specifications. Manyof the cheaper supplies carry out noisy or unstable power, which have the right to causenumerous difficulties with the system. Another problem through under-engineered powersupplies is the they have the right to run hot and force the system to execute so together well. Therepeated heating and cooling of solid-state contents eventually reasons acomputer mechanism to fail, and engineering ethics dictate the the name is aPC's temperature, the much shorter its life. Many human being recommend instead of theoriginal supply in a system with a heavier-duty model, i beg your pardon solves the problem.Because power offers come in common type factors, finding a heavy-dutyreplacement for many systems is easy, as is the installation process.

Inadequate Cooling

Some that the obtainable replacement power supplies have higher-capacity coolingfans than the originals, which can greatly expand system life and minimizeoverheating problems—especially for the newer, hotter-running processors.If device noise is a problem, models v special fans can run much more quietly thanthe typical models. These power supplies often use larger-diameter pan thatspin much more slowly, therefore they run much more quietly however move the exact same amount of air asthe smaller sized fans. Computer Power and also Cooling specialization in heavy-duty and also quietsupplies; Astec has several heavy-duty models as well.

Ventilation in a mechanism is also important. You have to ensure adequate airflowto cool the hotter items in the system. Numerous processors this particular day use passiveheatsinks that require a secure stream that air to cool the chip. If the processorheatsink has actually its very own fan, this is not much of a concern. If you have freeexpansion slots, friend should room out the boards in your device to permitairflow between them. Place the hottest to run boards nearest the fan or theventilation feet in the system. Make certain that enough airflow exists aroundthe difficult disk drive, specifically for those that spin in ~ high prices of speed. Somehard disks have the right to generate fairly a bit of heat during operation. If the hard disksoverheat, data deserve to be lost.

Always be sure to operation your computer with the instance cover on, specifically if youhave a loaded system. Removing the cover can actually reason a system tooverheat. With the cover off, the power supply pan no longer draws wait throughthe system. Instead, the fan ends increase cooling the it is provided only, and the rest ofthe device must be cooled by an easy convection. Although most systems execute notimmediately overheat because that this reason, several of my own systems, especiallythose that are totally expanded, have actually overheated within 15–30 minutes whenrun v the situation cover off.

In addition, be certain that any empty slot positions have actually the filler bracketsinstalled. If you leave these brackets off after removing a card, the resultanthole in the situation disrupts the interior airflow and also can cause higher internaltemperatures.

If you suffer intermittent problems that you doubt are connected tooverheating, a higher-capacity replacement power supply is normally the bestcure. Particularly designed supplies with extr cooling pan capacity likewise canhelp. At the very least one company sells a an equipment called a fan card, but I am notconvinced these room a great idea. Uneven the pan is positioned to attract air to orfrom the area outside the case, all it walk is blow warm air approximately inside thesystem and administer a spot cooling effect for anything the is blow on. In fact,adding fans in this manner contributes come the in its entirety heat inside the systembecause the fan consumes power and also generates heat.

CPU-mounted fans space an exception because they room designed only for spotcooling that the CPU. Numerous newer processors operation so lot hotter 보다 the othercomponents in the mechanism that a conventional, finned aluminum heatsinkcan't perform the job. In this case, a little fan placed directly over theprocessor gives a clues cooling effect that keeps the processor temperaturesdown. One drawback come these active processor cooling fans is the the processoroverheats instantly and also can it is in damaged if the pan fail. Anytime possible, tryto usage the biggest passive (finned aluminum) heatsink you deserve to find and also purchasea CPU pan from a trustworthy vendor.

Using Digital Multimeters

One straightforward test you deserve to perform top top a strength supply is to inspect the outputvoltages. This mirrors whether a strength supply is operation correctly and whetherthe calculation voltages space within the correct tolerance range. Note that girlfriend mustmeasure all voltages through the strength supply linked to a appropriate load, whichusually way testing while the strength supply is still mounted in the systemand linked to the motherboard and also peripheral devices.

Selecting a Meter

You need a basic digital multimeter (DMM) or digital volt-ohm meter (DVOM) to perform voltage and also resistance checks on digital circuits (see figure 3.17). You have to use only a DMM rather of the enlarge needle-type multimeters due to the fact that the older meters job-related by injecting 9v right into the circuit as soon as measuring resistance, which loss most computer system circuits.

Figure 3.17 A common DMM.

A DMM uses a much smaller voltage (usually 1.5v) as soon as making resistancemeasurements, i m sorry is for sure for electronic equipment. Friend can gain a great DMMwith countless features from several sources. I choose the small, pocket-size metersfor computer system work because they are easy to lug around.

Some functions to look for in a great DMM space as follows:

Pocket size. This is self-explanatory, but little meters areavailable that have actually many, if no all, that the features of larger ones. Theelaborate features found on some of the bigger meters are not really necessaryfor computer work.

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

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

Detachable probe leads. The leads conveniently can be damaged, andsometimes a variety of differently shaped probes are required for differenttests. Cheaper meters have actually the leads permanently attached, which method youcannot easily replace them. Look for a meter with detachable leads that pluginto the meter.

Audible continuity test. Back you have the right to use the ohm scale fortesting continuity (0ohms suggests continuity), a continuity test functioncauses the meter to develop a beep noise as soon as continuity exists in between themeter test leads. By making use of the sound, you conveniently can check cable assemblies andother items because that continuity. After you usage this feature, girlfriend will never want touse the ohms screen for this objective again.

Automatic strength off. This meters operation on batteries, and thebatteries can easily be worn down if the meter is coincidentally left on. Goodmeters have an automatic shutoff that transforms off the unit as soon as it senses noreadings for a predetermined period of time.

Automatic display screen hold. This feature enables you to organize the laststable reading on the display even after ~ the analysis is taken. This isespecially advantageous if you are trying to occupational in a difficult-to-reach areasingle-handedly.

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

Although friend can get a simple pocket DMM for as little as $20, one through allthese functions is priced in the $100–$200 range. Radio Shack tote somenice inexpensive units, and also you have the right to purchase the high-end models fromelectronics supply houses, such as Newark or Digi-Key.

Measuring Voltage

To measure voltages on a mechanism that is operating, you must use a an approach called ago probing top top the connectors (see figure 3.18). You can not disconnect any kind of of the connectors if the device is running, so you should measure with everything connected. Practically all the connectors you need to probe have openings in the earlier where the wires enter the connector. The meter probes space narrow sufficient to fit right into the connector together the wire and also make call with the steel terminal inside. The an approach is called ago probing due to the fact that you space probing the connector indigenous the back. You need to use this back-probing an approach to perform virtually every the complying with measurements.

Figure 3.18 earlier probing the strength supply connectors.

To test a strength supply for suitable output, check the voltage at the Power_Goodpin (P8-1 top top AT, Baby-AT, and LPX supplies; pen 8 top top the ATX-type connector) for+3v come +6v of power. If the measure is not within this range, the systemnever look at the Power_Good signal and therefore go not start or operation properly.In many cases, the power supply is bad and also must be replaced.

Continue by measure up the voltage varieties of the pins on the motherboard anddrive strength connectors. If you space measuring voltages for trial and error purposes, anyreading within 10% of the specified voltage is thought about acceptable, althoughmost manufacturers of high-quality power offers specify a tighter 5%tolerance. For ATX power supplies, the specification requires that voltages mustbe within 5% that the rating, other than for the 3.3v current, which have to be within4%. The adhering to table mirrors the voltage ranges 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 other voltages, although it is nominally +5v in most systems. The triggerpoint because that Power_Good is about +2.4v, but most systems need the signal voltageto be within the tolerances listed here:




Power_Good (+5V)



Replace the power supply if the voltages friend measure space out ofthese ranges. Again, that is precious noting the any and all strength supply tests andmeasurements have to be made v the power supply correctly loaded, which usuallymeans it need to be installed in a system and the mechanism must be running.

Specialized test Equipment

You have the right to use several types of specialized test gear to test power suppliesmore effectively. Since the power supply is one of the most failure-proneitems in pcs today, girlfriend should have actually these specialized items if you business manyPC systems.

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Digital Infrared Thermometer

One of the greatest additions to my toolbox is a digital infraredthermometer. They also are referred to as noncontact thermometers because theymeasure through sensing infrared energy without having actually to touch the item they arereading. This permits me to make prompt spot check of the temperature of achip, a board, or the system chassis. They are obtainable from service providers such asRaytek (http://www.raytek.com)for under $100. To usage these handheld items, you point at an item and thenpull the trigger. In ~ seconds, the display shows a temperature readout. Thesedevices are invaluable in checking to certain your system is adequatelycooled.