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Personal Computer PC Power Supply Maintenance

OddMix.com - PC Technical Note - PCN0703 - Karl Nagy

Picture 1. Power supply overview [14 KB]
Picture 1. Power supply overview

Personal Computer [PC] power supplies are taken for granted. Most casual users are not even aware that they have them. But a neglected power supply can destroy an otherwise perfectly good computer in a surprisingly small time. Maybe it is time to look into this subject from the prevention prospective.

The purpose of the computer power supply is to provide clean, regulated power to different parts of the computer system. Some of the PC's main power users require different voltages and currents in various degrees of smoothness or regulation. Until 1980 almost all of the regulated power supplies used to be analog types. These type of power supplies are usually connect to the main power source via a transformer, and has great regulation and not so great efficiencies. They are easy to design, cheap to build, and provide high isolation from the AC [Alternating Current] line voltage. Isolation provides good user protection to prevent electrical shocks.

Once switching regulator components became inexpensive and widely available, engineers redesigned power supplies completely. The large heavy, bulky and expensive line transformers disappeared, along with the 60 Hertz operating frequency. Modern day power supplies connect to the input voltage via a rectifier and capacitor. The AC line voltage thus converted to DC [Direct Current] is chopped up by a power oscillator circuit, running at much higher than 60 Hz line frequency. The higher operating frequency allows the use of smaller cheaper components, smaller power supply size and a lot higher overall efficiency.

Picture 2. - Dust on power supply - closeup [4 KB]
Picture 2. Dust on power supply - closeup
Two main problems exist in common PC power supplies. The first one is a serious design problem. Almost all PC power supplies have an internal fan. Its purpose is to provide aggressive air flow, to speed the heat removal from the power supply components. This heat is generated as a result of internal power losses. Unfortunately this air flow is moving the air from the computer housing through the fan and out to the outside of the computer's enclosure. This configuration also makes PCs built that way into good vacuum cleaners. As a result, dust accumulates within the computer, and quite a lot of it deposits within the power supply itself. On Pict. 1. and Pict. 2. dust buildup is readily distinguishable. These particles interfere with cooling, and in time they reduce airflow, by partially blocking the air exhaust opening. Some of this dust can also be conductive and combustible. Its periodic removal is highly beneficial for the longevity of the computer and it's power supply.

Luckily removal is a relatively simple affair. All it requires is a soft brush and a vacuum cleaner. In most cases power supply disassembly is not required. Brush anything within reach and the fan blades while vacuum. A can of "canned air" compressed gas can also be very useful, especially if it has a thin plastic tubing. With the tubing inserted into the power supply housing, lots of dust can be loosened up and vacuumed away. Repeat the insertion into as many different places as possible, and repeat the procedure. This "canned air" is really liquified gas. It costs around a few dollars a can and by the time cleaning is done, the can is usually history.

For that reason alone, it may be better to do a more thorough job. Make sure, the power line is disconnected, then carefully remove the power supply cover. It may be required to remove the power supply unit from the computer case. It will all depend on the computers construction. Carefully remove and save all screws and remove the sheet metal housing. Spend a minute or two just to admire the view. Note it if there are any burn marks, or if out of character, tell-tale signs are in evidence of impending disasters. Items like browned resistors, or printed wire boards are worth discovering. Changing charred resistors are a whole lot less expensive now than when it finally fails.

Picture 3. Power transistor mounting screw [7 KB]
Picture 3. Power transistor mounting screw
Picture 4. Transistor mounting screws [10 KB]
Picture 4. Transistor mounting screws
If everything seems to be in order, brush the dust and vacuum. When all is finally clean, it is time to tackle the second common power supply problem. Look for power semiconductors - transistors, integrated circuits, power rectifier diodes any and all items mounted to heat sinks with screws. In pictures 3, 4 and 5 arrows point to the locations of the power device mounting screws. With the appropriate size and type screw driver, one by one, tighten all of the screws. Because the repetitious heat cycles and the widely dissimilar expansion of the metals - copper, steel, and aluminum are most common - all screws needs to be retorqued.

Picture 5. Mounting screw location [6 KB]
Picture 5. Mounting screw location
If by rare chance all of the devices are secured to their heat sinks properly, as they should be via springs, make a note of the manufacturer and be happy to own a quality unit. When all power dissipating components are firmly reattached to their heat sinks, it is time for one final look.

Another extremely important maintenance item inside the power supply enclosure is the fan. Fans vary an amazing degree in quality. Underpowered power supplies usually have inferior fans which do not last long. Most fans do not have ball bearings. All bearings require a small amount of light grade oil periodically. Never reassemble an opened up power supply without lubricating the cooling fan. Good choice of lubricant is electric motor oil or sewing machine oil. Do not over oil. It may be necessary to remove the adhesive covered label from the fan's hub to uncover the bearings.

After the fan is lubricated, inspect everything very carefully. If all is in order, then reassemble all components reversing all earlier steps. Reattach the power supply to the computer's housing, and reconnect all cables to their proper places. Make sure all hard drives, CD, DVD and floppy drives are all properly plugged in, then close up the computer. Reconnect the line cord power cable and start the computer. Hopefully all is connected properly and up starts a freshly serviced, more reliable computer.

The cleaning procedure is a good preventive against thermally induced power supply failures. If a computer is operated in a forced hot air heated house, or in equally or more dusty environments, it would be necessary to check the condition of the inside of the computer and the power supply unit more often. A simple check with a flashlight would be all that is necessary to determine if a repeat cleaning would require.


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