1. Panel compression method uses the function of each switch and knob exposed outside of the electrical panel, the console or the machine to check and roughly judge the location of the fault. For example, the TV sound is sporadic sometimes, and the volume knob is adjusted to appear “Kluck” sound accompanied by sporadic sound, then it can be known that the volume potentiometer has poor contact.
2. Direct inspection method is to check and judge the location of fault by seeing, touching, hearing and smelling. This method is particularly suitable for obvious faults such as hot, burnt smell, ozone smell and abnormal sound. For example, there is a “crack” sound inside the TV after turning it on, the image jumps with the sound and a strong smell of ozone is smelled, then it can be judged that the line output transformer or high-voltage part is igniting.
3. Voltage measurement method is to check the supply voltage and the voltage of relevant components by use of multimeter, especially the voltage at key points. This method is the most basic and commonly used inspection method for the maintenance of household appliances.
4. Electric current measurement method is to measure the total current and the working current of transistors and parts by use of appropriate current range of the multimeter, so as to judge the fault location quickly. For example, the TV is often burned with DC fuse and the total current of the measured regulated power supply is greater than the normal value, the line output stage circuit is disconnected and the current returns to normal, then it can be determined that the fault is in the line output stage and subsequent circuits.
5. Resistance measurement method is to judge the fault location by measuring the resistance value of resistance, capacitance, inductance, coil, transistor and integrated block.
6. Short-circuit method refers to the AC short-circuit method, which is particularly effective for determining the range of steamboat sound, howling sound and noise. For example, if you want to judge the howling fault of the radio, you can use a 0.1μF capacitor to short-circuit the collectors of the converter tube, the first intermediate amplification tube and the second intermediate amplification tube to the ground, respectively. The howling disappears at a certain stage of short circuit, the fault occurs at this stage.
7. Circuit disconnecting method is to compress the fault range by cutting off a certain circuit or unsoldering a certain component and wiring. For example, the overall current of an electrical appliance is too large, the suspicious part of circuit can be gradually disconnected. The fault will be at the stage where the current returns to normal when it is disconnected. This method is often used to repair the fault of excessive current and fuse burning.
8. Knocking method is to judge the fault location by use of a small screwdriver handle or a wooden hammer to gently knock a certain place on the circuit board and observe the situation (Note: it is generally not easy to knock the high-voltage part). This method is particularly suitable for checking the fault of false welding and poor contact. For example, there is no sound in the TV image sometimes, you can gently knock on the TV shell with your hand, and the fault is obvious. Open the back cover of the TV, pull out of the circuit board, and gently knock the suspicious components with screwdriver handle. The fault is in this part where the fault is obvious when it is knocked.
9. Replace inspection method is to replace the component that is considered to be faulty by use of a good component. This method is simple and easy to operate, and often has twice the result with half the effort.. It is commonly used to replace tuner, line output transformer, capacitor below 0.1μF, transistor, integrated block and so on.
10. Signal injection method is to find the fault location by injecting the signal of the signal generator into the faulty circuit. This method is generally used to repair complicated fault.
11. Interference method is to judge the fault location by using the metal part of the screwdriver and tweezers to touch relevant detection points, watch the clutter response on the screen and hear the “Kluck” sound of the horn. This method is often used to check public channel, image channel and sound channel. For example, no image or sound fault is detected, pick up the screwdriver to touch the first intermediate amplification base. If there is clutter response on the screen and the horn has “Kluck” sound, it indicates that the circuit is normal after intermediate amplification, so the fault is in the tuner or antenna.
12. Comparison method is to find the fault location by comparison of the voltage, waveform and other parameters of the normal machine of the same model with the faulty machine. This method is most suitable when the circuit diagram cannot be found.
13. Heating method is to quickly judge the fault location by heating up the suspicious component, so as to accelerate the “death” of such component. For example, the line width of a TV is normal when it is just turned on, and the line width retracts a few minutes later, the shell of the line output tube turns yellow and the line tune is hot, then you can take a soldering iron to approach the line tube to heat it up. If the line width continues to retract, it can be judged that the line tube has a fault.
14. Cooling method is to quickly judge the fault location by cooling the suspicious components. This method is used for regular fault, for example, it is normal when turning on, but abnormal after a while. Compared with the heating method, it has the advantages of fast, convenient, accurate and safe. For example, the field amplitude of a TV is normal after turning on, but it will be compressed after a few minutes and form a horizontal broadband after half an hour, the field output tube feels hot when touched by hand. At this time, put the alcohol ball on the field output tube, and the field amplitude begins to rise and the fault disappears soon, then it can be judged that it is caused by the thermal stability of field output tube.
15. Procedure diagram inspection method is to find the fault location by narrowing the fault scope step by step according to the fault maintenance procedure diagram.
16. Comprehensive method is to use a variety of methods to check some more complicated faults.
Post time: Nov-29-2021