Computer power knowledge, power supply maintenance and repair

Computer Shop News Generally speaking, the sound of the computer during normal operation is very small. In addition to the sound of the hard disk reading and writing data, it is mainly the sound of the cooling fan, especially the sound of the switching power supply fan. Some switch power supplies will generate some noise during operation for a long time, mainly due to the poor rotation of the power supply fan. There are many reasons for the noise of the power supply fan to rotate, which is mainly concentrated in the following aspects:

--The axial deviation of the fan motor bearing sleeve causes the fan blade to be stuck or rubbed. The sound of "burst".

--The fan motor bearings are loose, causing the blades to sound "嗡嗡" when rotating.

--The fan motor is axially swayed. Due to the wear of the gasket, the axial clearance increases, and the sound of the "burst" is emitted after power-on.

--Inferior lubricating oil is used in the fan motor bearing. When the ambient temperature is low, it is easy to condense with the dust entering the fan bearing, which increases the resistance of the motor rotation and causes the motor to emit "嗡嗡" ;the sound of.

If the fan does not work properly, it may burn the motor after a long time, causing damage to the entire switching power supply. For the reason that the above power supply fan makes a sound, the following maintenance work is usually required.

The power box is the easiest place to collect dust. If the sound from the power supply fan is loud, the fan should be removed every six months to clean the dust and add some lubricant for simple maintenance. Since the power supply fan is enclosed in the power supply box, it is not convenient to disassemble, so be sure to pay attention to the operation method.

(1) Disconnect the fan and disconnect the power supply from the main unit. Unplug the input and output cables on the back of the power supply. Then unplug and connect all the accessories connected to the power supply, remove the fixing screws of the power supply box, and take out the power supply box. Observe the appearance of the power box, remove the screws reasonably and accurately, and remove the cover. When taking the cover, pull the wires out of the gap at the same time. Remove the four screws that secure the fan and remove the fan. You can not solder the two power cables.

(2) After cleaning the dust-proof cardboard to isolate the power circuit board and the fan, use a small brush or a damp cloth to wipe the dust and wipe it clean. It is also possible to use dust from the fan to blow fan blades and bearings.

(3) Apply grease to tear off the self-adhesive label and use a needle-nosed pliers to pick out the rubber seal. When you find the motor bearing, add lubricant and push the fan by hand to make the lubricant flow evenly along the bearing. Usually add a few drops. Pay attention to whether the fan of the ball bearing has two bearings. Don't neglect the oil feeding to the bearing on the air inlet surface. Do not put the oil on the main shaft.

Lubricants must use computer-specific lubricants or advanced lightweight sewing machine oils. Never use lubricants used in general automobiles. Finally, install the rubber seal and label it.

(4) If the fan sends out a large "burst" noise, it is generally impossible to solve the problem by cleaning the dust and lubricating oil. At this time, the fan will be found after disassembling the fan. The blade slides in the axial direction at a large distance. After taking out the rubber sealing piece, use a needle-nosed pliers to separate the snap ring on the shaft. Below is the gasket. At this time, the fan rotor can be taken out (connected with the fan blade). The original gasket is used as the standard and the thin plastic sheet is made of moderate thickness. Make a gasket. Put the prepared gasket between the original gaskets. Be careful not to place the gaskets too thick and keep a certain distance in the axial direction. By turning the blade by hand, the fan can rotate smoothly. Finally, attach the snap ring, rubber seal and label. Remember the small parts on the main shaft, such as gaskets, rubber seals, springs, etc., so as not to know how to reset them.

In short, the power supply is the driving force of the computer. If the power supply fan fails, the consequences are serious. Therefore, the power supply should be maintained and maintained regularly.

According to the data, the fault caused by the power supply accounts for 20%~30% of the total number of failures of various components of the computer. The fault detection and repair of all parts of the host must also be based on the normal power supply. Below we will discuss some common faults of the power supply. The microcomputer power supply is generally prone to the following faults: the fuse is blown, the power supply is not in the transmission, or the output voltage is unstable, the power supply has an output but the power is not displayed, and the power supply load capacity is poor. The following describes their maintenance methods:

1. Fuse blow fault analysis and troubleshooting

When such a fault occurs, first open the power supply enclosure and check whether the fuse on the power supply is blown. Based on this, it can be determined whether the inverter circuit has failed. If yes, it is caused by the following three situations: one of the bridge rectifier diodes in the input loop is broken down; the high voltage filter electrolytic capacitors C5 and C6 are broken down · and the inverter power switch tubes Ql and Q2 are damaged. The main reason is that the DC filter and the oscillating circuit work for a long time in a high voltage (10 300 V), high current state, especially when the AC voltage changes greatly and the output load is heavy, the fuse blows easily. The DC filter circuit consists of four rectifier diodes, two 100k & Omega; left and right current limiting resistors and two electrolytic capacitors of about 330uF; the conversion oscillator circuit is mainly composed of two high-power switch tubes of the same type mounted on the same heat sink.

After the AC fuse is blown, turn off the power plug. First, carefully observe whether the appearance of each high-voltage component on the board is broken by burnt or electrolyte. If there is no abnormality, use a multimeter to measure the value of the input: If it is less than 2OOkΩ, it means that there is a partial short circuit at the back end, and then measure the resistance between the two high-power switch tubes e and c respectively; if it is less than 100kΩ The tube is damaged. Measure the resistance of the four rectifier diodes, the reverse resistance and the two current limiting resistors. Use a multimeter to measure the charge and discharge to determine whether it is normal. In addition, when replacing the switch tube, if the substitute product cannot be found and the substitute is selected, attention should be paid to the collector-emitter reverse breakdown voltage Vceo, the maximum allowable dissipation power of the collector Pcm, and the collector-base reverse stroke. The parameter of the voltage Vcbo should be greater than or equal to the parameters of the original transistor. Another thing to note is: Do not directly detect the damage of a component when it is damaged. It is very likely that the other high-voltage components will still be damaged and the replacement components will be damaged. It is necessary to thoroughly check all the high-voltage components of the above circuit to completely eliminate the fuse blown fault.

2. No DC voltage output or voltage output is unstable

If the fuse is intact, there is no output of DC voltage at all levels under load. The possible causes are: open circuit and short circuit in the power supply; overvoltage and overcurrent The protection circuit is faulty; the oscillation circuit is not working; the power supply load is too heavy; the rectifier diode is broken down in the high-frequency rectifier filter circuit; the filter capacitor is leaking.

The processing method is: use a multimeter to measure the ground resistance of the system board's 10V power supply. If it is greater than 0.8Ω, the system board has no short circuit. The microcomputer configuration is changed to minimize, that is, only the main board, power supply, and buzzer are left in the machine, and the DC voltage of each output terminal is measured. If there is still no output, the fault is in the control circuit of the microcomputer power supply. The control circuit is mainly composed of an integrated switching power supply controller (TL-496, GS3424, etc.) and an overvoltage protection circuit. Whether the control circuit works normally is directly related to the DC voltage output. The overvoltage protection circuit is mainly composed of a small power transistor or a thyristor and related components. The multimeter can be used to measure whether the triode is broken down (if the thyristor is soldered, the relevant resistance and capacitance are damaged).

3. The power supply has an output, but the power is not displayed.

The possible cause of this failure is that the "POWERGOOD" input Reset signal has insufficient delay time, or "POWERGOOD" has no output. After booting up, use the voltmeter to measure the output of "POWERGOOD" (connect the 1 pin of the mains power plug). If there is no 5V output, check the delay component. If there is 5V output, replace the delay capacitor of the delay circuit. Just fine.

4. Poor power load capacity

The power supply works normally when only the main board and floppy drive are powered. When the hard disk, optical drive, or memory module is connected, the screen becomes self-operating. The possible causes are: the transistor operating point is not selected well, the high voltage filter capacitor is leaking or damaged, the Zener diode is heated and leaked, and the rectifier diode is damaged.

Change each transistor in the tank to increase its gain or increase the operating point of the transistor. After detecting the defective part with a multimeter, replace the thyristor, Zener diode, high voltage filter capacitor or rectifier diode.