An inside view of an older style television using a flyback transformer.
Older style televisions with glass picture tubes required a high voltage supply to operate. A transformer known as a flyback transformer steps up the AC (alternating current) used in the horizontal oscillator circuit to provide 20,000 to 50,000 VDC to the picture tube. The high voltage source travels through a highly insulated cable with a wire clip on the end (known as the anode) and is attached to the side of the glass picture tube via a hole in the rear of the tube. A high-voltage capacitor is attached to or built into the flyback transformer.
Instructions
1. Turn on the TV. Is there a raster (display on picture tube)?
A raster indicates the flyback transformer and capacitor are working.
If there is no raster but a momentary static sound coming from the back of the set, then you are getting high voltage and possibly the picture tube is faulty.
Otherwise, the problem could be a faulty capacitor, flyback transformer or horizontal output transistor.
2. Leave the TV unplugged for a few days to make certain that any high voltages inside the TV have dissipated. Remove the screws from the back cover and separate the cover from the TV.
3. With the aid of a service manual, locate the capacitor that is attached to the flyback transformer and observe the value stamped on the capacitor.
Some TVs have the capacitor built into the flyback transformer and when faulty, the flyback transformer will require replacing.
4. Unsolder one leg of the capacitor from the circuit board. Lift the unsoldered end up and away from the board.
5. Select the "ohm" position on the multimeter and set the dial to a high resistance reading. Touch one probe to the capacitor fixed leg on the board and the other probe to the free leg.
6. A reading on the meter indicates a shorted or leaking capacitor and it should be replaced. If there is no reading on the meter, then the capacitor probably is not faulty.
Confirm this by using a digital capacitance meter. Connect one probe of the meter to the free leg of the capacitor and the other to the fixed leg.
7. Select the capacitance range of the meter to match the value shown on the capacitor.
Read the value and compare the reading to that shown on the capacitor.
If the reading differs by more than 30 percent in value, the capacitor should be replaced with a capacitor of the same part number listed in the service manual.
8. If the capacitor checks out okay, resolder the free leg back onto the board and continue to troubleshoot the problem.
9. If a new capacitor has been installed, keep hands and tools clear of the TV and plug the set in and turn it on. If the TV is working, then turn it off, unplug it and replace the back cover.
Tags: flyback transformer, picture tube, high voltage, back cover, built into, built into flyback