Using the 555 integrated timer. Add a small amount of external components, can be made simple and practical short-circuit tester between coils. Using it is simple, accurate determination of line output transformers, switching transformers, line transformers and deflection components to promote the existence of inter-turn short circuit loop.
First, the circuit structure
555 circuit is a powerful, flexible, widely used in integrated circuits. 8-pin dual in-line structure. Within the 3 ~ 18V can work properly.
Produced using 555 circuits between coils of electric short-circuit tester, such as photo shown in the schematic. 555 circuit and external components, the multivibrator. 3 square wave pulse foot by coupling the output via C5.
Tester can be installed on a volume of 65 × 50 × 40mm. DC power supply plastic box. Compact. Easy to use. AC voltmeter with a refrigerator delay regulator is commonly used in micro-modified form of AC voltage from the table: the original conversion, respectively literally scrape the surface of 100,200,300 the last three digits of a 0. Will replace the original high-frequency rectifier diodes 1N4007 rectifier diodes. Access to known 30V, 50Hz AC voltage. Appropriate adjustments to the original partial pressure decreasing and the size of resistance, so that the pointer refers to the 30V line to the scale.
Figure 1, the timing capacitor C3 and the output coupling capacitor C5 to a good high frequency characteristics of selected high-frequency ceramic capacitors or film capacitors. Output J1, J2 connected two wires with alligator clips soft.
Second, the use
No-load tester. Table showing the number of AC voltage is about 1V. Output with an oscilloscope measurement of the square wave pulse for the 5Vpp regulate RP. Square wave pulse frequency can vary between 12.5 ~ 25kHz.
Test, the test device output ports J1, J2 respectively, then the two ends of the inductor under test. Measured coil inductance L and the composition of output coupling capacitor C5 in series circuit. Regulation RP, square wave pulse when the output frequency is equal to the natural frequency of LC series circuit, the voltage meter shows the largest number. If the measured inductance of the coil is larger (such as color TV’s "FBT" primary coil inductance 3.26mH), no winding inter-turn short circuit. Table showing the number of voltage up to 30V. If the coil with an oscilloscope as a measurement of amplitude 80Vpp. Period of 80us (frequency of 12.5kHz) sine wave. If the measured inductance of the coil is small (such as the line drive transformer secondary is 0.427mH), said voltage meter maximum number of 16V. With the oscilloscope measurements 35Vpp sine wave cycle 30 us.
When there is inter-turn short circuit test coil, the coil’s Q value of the significant decline in the number displayed when the voltmeter will be greatly reduced.
1 line output transformer (FBT) of inspection
(1) independent testing: will be measured "FBT" down from the circuit board welding, for color television or color monitor "FBT", will test the two input device termination "FBT" the primary winding (+ B-side and C-side). For black and white TV’s "FBT" step-up capacitor and damping diode connected connector, adjust the voltage meter RP said the maximum number of UL. No inter-turn short circuit "FBT". Table showing the number of voltage is generally between 20V ~ 30V. With the wire in the "FBT" the core of a turn around on the wear will be connected at both ends, made one turn short circuit loop, when the voltage table showing the number of Uo down to 2V or so.
No inter-turn short circuit "FBT", UL/Uo8, inter-turn short circuit within the existing "FBT". UL greatly reduced, UL/Uo3, short-circuit the more serious, UL’s is smaller. As no inter-turn short circuit "FBT" and the existence of inter-turn short circuit "FBT" Table showing the number of voltage is very different. The tester can be used to accurately determine the "FBT" the existence of inter-turn short circuit.
(2) Road test: "FBT" when mounted on the circuit board. Windings are connected as a first-class external components can plug and unplug the CRT deflection coil tail, reducing external components on the measurement results. In the road test, the voltage is generally greater than the table shows the number of 15V, but in the way the measured UL is very small, short-circuit may be caused by external components. Under the board from electric welding needed "FBT" independent testing, to prevent miscarriage of justice.
2. Switch transformer testing
(1) independent testing: the switch to the transformer from the circuit board to test the output of the termination of the primary winding of switching transformer (300V-side and C side), adjust the RP so that the maximum UL and different types of switching transformer, voltage meter shows the number of general In 20 ~ 30V, between the coil turns wearing a short circuit around the ring, Uo is about 3V, UL/Uo6. Exist within the inter-turn short circuit switching transformer, UL’s value is very small, and the more serious when the inter-turn short circuit, UL’s is smaller. When wearing a short loop around a turn, the voltage drop table showing the number of very small, UL/Uo2.
(2) Road test: As the primary winding of the connected components and the secondary winding damping the impact of external components connected, different movements measured by the UL values vary greatly. To reduce the error, can be used to suction tin tin primary winding of a pin or needle aspiration to a clean pin and circuit board separately. Further testing. If the measured UL is small, it may be caused by external components, the need for independent testing.
Detection of the line drive transformer 3
Will be pushed forward down transformer from the circuit board welding, testing the output of the termination line drive transformer secondary winding to regulate the RP to UL’s largest, non-promotion of inter-turn short circuit line transformer. Table showing the number of voltage 16V in general about wearing short turn around a ring, Uo generally around 2V. UL/Uo6. To promote inter-turn short circuit line transformer, UL’s value is much smaller, wear ring around one turn short circuit, the voltage dropped off the table show the number of very small, and the more serious turn to turn short circuit, UL’s is smaller.
To do with the silicon core of the line drive transformer, UL and Uo are small, can not use this tester to detect the judge.
Detection of the line deflection coil 4
The deflection coil to take down the plug from the circuit board to test the output of the termination line deflection coil input, adjust the RP to UL maximum. No inter-turn short circuit in the line deflection coil 22V in general about UL. If the measured UL smaller, the line deflection coil can then separate the two windings, respectively, the UL test their values, no turn to turn short-circuit the line deflection coil, the two UL approximately equal value, if the two were quite different. The line deflection coil memory in the inter-turn short circuit. The line deflection coil can be further taken down from the tube, close to the line deflection coil to make a short loop, detect Uo, no turn to turn short-circuit the line deflection coil 16V in general about Uo. As the line between the deflection coil windings using loosely coupled, non-inter-turn short circuit line deflection coil, UL/Uo1.3, turn short circuit between the line deflection coil UL/Uo1.2.
Third, a description of the test results
For different coil, the L, Q and the coupling between the different windings, the coils with a short-circuit tester between the UL and Uo measured relatively high dispersion. For the line output transformer, switching transformer and line inductance of such a large amount of drive transformers, Q value is high and the use of tight coupling between the coil inductance coil, the UL/Uo6, can be simply and accurately determine the existence of winding inter-turn short circuit. For this type of line deflection coil winding inductance coil between the use of loosely coupled, non-inter-turn short circuit line deflection coil UL/Uo1.3, and turn to turn short-circuit line existing partial coil UL/Uo1.2. As long as the detection of attention in the usual accumulation of experience, can also be measured more accurately determine the existence of inter-turn short circuit loop.
Since these inductors are available independently or in the way the machine is not powered on for testing. Therefore the use of the coils short circuit tester measuring inductance coil inter-turn short circuit exists, is not only simple, accurate, and safe.