Saturday, January 22, 2011

【 Weak current College 】 repeated burning monitor fuse several examples of typical fault analysis 】

Many friends have the monitor's fault, will be helpless. Monitor internal pressure, many daunting, but really can repair the monitor station is very small. In fact, just a little electronic basis, using a multimeter and electric iron, for some small failures, the monitor is able to solve.

I have a batch of old unit 14-inch monitor, long after the warranty period. There are a number of the monitor's fault, post no display, multimeter electric barrier test power input, the resistance is infinite, the power cord is open. Power on the system check and found that the Board of fuse fuse, swap a new fuse, power on the fire insurance. Author it maintenance, fault found are concentrated in a few components, and several components are easy to buy, replace it. Therefore, if friends encounter similar failures, can start with these components, thereby fixing monitor failure.

Monitor internal pressure, although they do not cause life-threatening, but it was a shock of taste or feel. Therefore, the maintenance of the monitors, in order to avoid the high voltage electric shock, you can monitor the electricity let within residues. Monitor internal can save electricity component is filter capacitors, is the larger of cylindrical components, with the insulating layer of pliers to touch the two filter capacitor, when you hear a PIN "snap" of a sound, sparks, description of electric filter capacitor has been sent, you can rest assured that check. Lead post shall burn insurance of elements are filter capacitors, degaussing resistance, tube, etc.

■ Filter capacitor

The monitor is generally is to use the power switching power supply, access, rectification, first going through the filter, make the DC and AC transform, transfer to another device to use. In order to eliminate and prevent from various interference power grid, you must use the electrolytic capacitor filter (shown in Figure 1), and electrolytic capacitors is the crossover in DC voltage polarity, a separated DC, communication. When filter capacitor used for a longer time, electrolyte solidification, easily lead to internal breakdown and short circuit, so that by the fuse on excessive current, causing the fuses. Therefore, encounter a post that is burning the insurance, you should first check whether the filter capacitor short-circuit, check the method is simple, using a multimeter electrical capacitance of the short-circuit resistance value is 0, good filter capacitors have a charge and discharge procedures, the resistance. This capacitor voltage value is generally high, you can use the same types of TV are capacitor instead.

There is also a case of failure, no fire insurance, check filter capacitor without problems, but in the back of the circuit, and received a promise of capacitance, the relatively large size of the capacitor, multimeter check revealed that resistance to 0, or is there an internal breakdown of failure after troubleshooting, replacement.

■ Degaussing resistance

A CRT monitor works produced-beam tube, deflection coil under electron impact of Phosphors on the screen, so that the corresponding point on the screen. The monitor is easy to produce appears around the magnetic field of goods, such as multimedia speakers, various peripherals, such as the transformers, the electron beam magnetic field affects the direction of deflection. Therefore, in order to ensure that the display quality, while the monitor is powered on, it sets a degaussing circuit. Degaussing circuit by degaussing coils and degaussing resistance, by degaussing coil produces a strong magnetic field, you can eliminate the excitation. Degaussing resistance is actually a thermistor (Circuit Board on the square, there are three pin components), its cold resistance is generally 12 ohm ~ 47 ohm, when commercial power is, the resistance is low, degaussing coils have electrical work, degaussing coils of operating current is large, so the temperature resistance of degaussing, the resistance to increase dramatically, resulting in the electrical current flowing through degaussing coils has dramatically decreased, complete the degaussing process.

From degaussing resistance works is not difficult to see, when degaussing resistance thermal resistance value gets smaller, or degaussing resistance internal breakdown, the resistance of the smaller, you can view the degauss resistance bad or damaged. You can set the degaussing resistance down, hair dryer, heating, it should be their resistance with temperature but increased, if no change after heating or change is small, you can view the degauss resistance to damage. If you determine that the degaussing resistance is damaged, you can use the same specification, if it is not found, or a difference of a grade of degaussing resistance instead. But the probability of damage degaussing coils, can not be considered.

■ Output tube

There are a few cases on fire insurance of failure to check the filter capacitance and resistance are not degauss, finally check the output pipe, discovery line output tube has been breakdown short circuit. Line output tube general installation at the edge of the output transformer, has three pins. Can be removed, if the resistance between the three pins are very small, you can view the output pipe damage, looking for a change of the same model.

Appear on fire insurance of failure but also many, such as rectifier diode breakdown, power switching valve damage, etc., as long as you carefully check to identify the point of failure, replace it. As for the engine room staff, there are many favourable conditions, the engine of the machine are generally the same model, when the discovery of a machine failure, identify suspect in failed components, direct replacement, use of elimination, find the point of failure, the replacement component.

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