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How to test flyback transformer and when to replace it

Flyback transformers are the most important of all transformers. As they are used for power supply and to generate current they are also called line output transformers. It generates the voltage in different ranges. It is able to conserve the energy that is stored for a considerable time of the switch period. It helps to transfer and store the energy for a certain period till it is switched on. It is also smaller than other transformers. It also helps to prevent accidents. The direct current and the alternative current which is converted into direct current using high voltage, is stored by the flyback transformer.

Flyback transformers thus play a vital role in power supply and they have to be in good working condition. Many flyback transformers work well for only two years and then develop faults so that it becomes necessary to test and replace them. They develop faults because they are not properly built and are badly designed using low quality material. So, testing becomes a very important issue. You should know what faults can be developed to test them.

Some of the faults are discussed here. The primary winding can have a shorted turn and the secondary winding can have an open or shorted internal capacitor. Both these conditions have to be tested. A bulge or a crack in the transformer can be seen. The external arcing to the ground and internal arcing between windings can be heard and set right. There can be shorted high voltage diode in the internal part of the secondary windings which can be tested with a multimeter. The screen voltage divider can cause blurred images and this can be set right by having a new 'monitor blur buster'. This is applicable only to 14 inch and 15 inch monitors. When they operate at a full capacity, they can breakdown and this can be tested by having a good working flyback transformer having a similar design. There can be short circuit between the primary and secondary windings. This can be checked by using an ohm meter to measure between both the windings. A shorted turn or open in the secondary winding generally does not occur.

1. If the primary winding is shorted there will be certain signs that will be visible. Since there is no high voltage, there will be no display. The power will blink. There will be a voltage drop in the B+. Along the B+ line, the components will develop faults. The horizontal output transformer will get shorted after becoming very hot. At times, even the power section can blow up.

2. To test the primary winding in a flyback transformer and check its condition, you can use the flyback/LOPT tester. It will identify the fault in the winding even if it is only one shorted turned. It is very handy and can be used easily. You have only to connect the probe to the primary winding. This can also test the B+ coil and the switch mode transformer power winding.

3. If the capacitor is shorted there will no display and the B+ voltage will drop, the secondary diode will be burned or shorted, the horizontal output transistor will be shorted, there will blinking of the power and sometimes the power section will blow. Sometimes the circuitry parts of the automatic brightness limiter (ABL) can also get burned.

4. You can also have the capacitor open and this will also show some signs. There will high voltage shut down. After a few hours or days after the horizontal output transistor is replaced it will blow up. There will either be distorted display or intervals of 'no display'. The horizontal output transistor can also become shorted and cause the power section to blow up.

5. You can check if the internal capacitor is open or shorted by testing with an analog multimeter and digital capacitance meter. You should keep the multimeter at the right range. And then keep the probe to the anode and the cold ground. The anode cap should be removed to get the correct reading. If the monitor chassis is ground then you will have cold ground. The multimeter will help check if the internal capacitor is shorted. If there is no movement of the needle then it means that the capacitor is functioning properly. You can confirm this by using the digital capacitance meter to know whether it is within the range (2.7nf) that it should be. If it is 0.3nf, then it means that the capacitor is open.

If the capacitor is shorted or open, you can get a new flyback transformer or send it to be repaired or try to repair it. Sometimes you have internal capacitors that are connected to the circuits instead of the ground.

Flyback transformers need to be tested and replaced whenever necessary. Faulty wires and designs can cause a lot of problems. The particular fault has to be identified and proper equipment used to test it. Then the fault has to be rectified so that the transformer can be put back to a working condition. If this cannot be done, it has to be replaced. Make sure you buy good quality flyback transformers and get the right person with knowledge about these transformers to repair it. Get enough information from the internet or other sources before you repair or replace it. You can obtain the diagram of the flyback transformer and its circuit from the internet and this will help you to understand its workings and you might be able to identify the faults and go about the process of repairing them. If all this fails, then you will have to replace it.