The Main Power Supply

The next step in troubleshooting would be to check the main power supply. First, check the bridge rectifiers. A bridge rectifier could be a combination of four silicon diodes or a square rectangle type package. Use the diode function on your multimeter and see if there’s a short across one of them, or perhaps between the pins of the rectifier block. If there’s no short there, measure across the main B+ filter capacitor, but make sure you discharge it as described earlier! If there’s a dead short there, take out the cap or disconnect one end to see if it’s shorted. If not, reinstall or resolder, then measure the transistors and diodes around the power supply area. If you don’t find a short with one of those components, go to the horizontal/sweep power supply circuit.

The Horizontal Output Transistor & Flyback

First, locate the horizontal output transistor. This is found very close to, or next to, the horizontal output transformer (also known as the flyback). The flyback should be on an aluminum heat sink, or on the side of the metal chassis. Disconnect or unsolder two of the three legs of the transistor. Measure it with your meter, or plug in the set with the light bulb attached across the fuse.

If the transistor is shorted, or the light bulb doesn’t glow bright anymore, replace the transistor

and plug back in. If the light bulb glows bright again, you must replace both the flyback and horizontal output transistor simultaneously. In some cases this will fix the set, but sometimes there are multiple problems with a set.

Go to where the flyback is, and start measuring the diodes and capacitors on the flyback itself. If you don't find any shorts there, it could be a shorted vertical output IC, a shorted sound IC, a shorted disc capacitor in the Hi Voltage/sweep circuit, or in rare cases, a shorted capacitor or tuner.

Final Thoughts

You will find the short in the board if you're persistent. Just remember, do not replace the fuse if the bulb stayed bright, as this could cause additional damage to the set. I have experienced a few occasions where lighting has hit a cable or electric line outside, and damaged every IC in the set.

The fixes described here are general, common problems that occur when a television set goes dead. Remember that working inside of a television should never be taken lightly, and that safety should always come first.

by Larry Dillon

Image and editing by Matt Whitlock

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