Checking FBT

[Andre]

Somebody can you tell me how to know a Fly back is good or not..I really need itl. thx

[Guest]

Drop it on the floor, it if bounces, it's good. If not, junk it.

[Frank]

[frank]

http:www.electronica-pt.com/index.php/content/view/177/

[torbjorn]

If you don't own a specialized FBT tester, another possibility is measuring the inductance of the primary winding with a LCR meter. Usually, it is a few mH and, when measured at about 10 kHz, the losses should be very low (high Q factor). Sure signs that the FBT has shorted turns is that the Q factor is low or that you get very different inductance readings when testing at different frequencies.

Lacking a LCR meter, it is also possible to make provisional hook-ups with a tone generator and an oscilloscope. For example, you can connect the primary winding in series with a resistor, supply the whole circuit with a sine voltage of, say 20 kHz and connect the oscilloscope so that you can view the voltage across each of the components. Adjust the resistor so that both voltages are approximately equal, then you should be able to see a 90 ° phase shift between the voltages (either by using both channels of a double channel scope or by X-Y connecting the scope and looking at the lissajous figure). Try halving or doubling the frequency, if the FBT is in order then you should have to halve or double the resistor value to get equal voltages again.

However, you will not surely find faults at the internal rectifiers or possibly integrated bleeder resistors, focus voltage networks etc by this method.