For those problems that occur after the set warms up, you can use what's called a circuit chiller. This allows you to spray the suspected parts to see if the problem goes back to normal. These sprays come with a small extension tube that you put onto the spray nozzle so you can localize a bad part easier.

For those problems that do not happen right away, but instead get worse as the set warms up, use a simple hairdryer and a cardboard nozzle to direct the heat to a more centralized area on the circuit board and suspected components to make the problem occur. When (if) this happens, use the circuit chiller to see if the problem goes away. If it does, you got lucky and found the intermittent part.

Intermittent problems can be the most costly and time consuming types of repairs. When you cannot find the intermittent component, there could be a small crack in the printed circuit board.

Preventive Maintenance on your TV Set

The preventive maintenance on your TV set is easy, and if followed can help the TV set last longer.

• Keep the outside cabinet clean and do not block the vent holes or slots.
  
  
• Allow adequate ventilation - TVs use more power than any of your other A/V components. Heat buildup takes its toll on electronic parts. Leave at least 3 inches on top and sides for air circulation if the entertainment center does not have a wide-open back panel. Do not pile other components (like VCRs) on top of the TV.
  

• Clean the surface of the picture tube front with a soft cloth barely dampened with clean water, and if needed, a mild soap detergent. Never apply water, spray a glass cleaner, or a wet cloth directly onto the surface of a picture tube. Doing this can cause a serious circuit failure due to moisture seeping around the edges of the picture tube and dripping on the circuit board directly under the tube.
  
  If you have not cleaned your tube off in a week or two wipe it down and you will probably be amazed at the amount of filth and dirt that gets attracted to the front of a TV set. This is especially true for smokers, as the tar and nicotine will build up fast on the picture tube face. I once went out on a service call where the customer was complaining of a dull and weak picture. As soon as I looked at the set, I knew what the problem was. I licked my finger and ran it across the front of the TV set and wow, the brightness poured out of the TV set. To say the least, the customer was quite embarrassed.
  
  
• It's important to clean the inside of the TV before you work on it.
  
  First, locate all of the Hex or Phillip type screws that hold on the back of the set. With the back off you'll undoutedly wonder why it is so dirty in there. The high voltage sucks in most of the dirt that gets airborne in the room when the room is cleaned.
  
  With the back off, use a new paintbrush and a small nozzle attachment of a vacuum cleaner. Be very careful and do not apply too much pressure while brushing off the built up dust. While true you could use compressed air, it will make a mess all over the room, and the dust is not a healthy thing to be breathing in.
  
  Do not try to tighten anything like screws or turn anything that you do not know what it is. They may be a critical adjustment. Also, be very careful of the Picture tube neck and anything mounted to it. The picture tube neck is very thin glass and won't take much before it snaps. The components mounted on the neck should not be disturbed as well.
  
  Mounted on the neck of the picture tube is the deflection yolk, and the rings are the convergence and purity magnets. Just as a precaution, I will mark those rings on the neck with some type of marker in case I hit them by accident. Some larger tube sets have a small circuit board attached to the neck. This board is the beam velocity modulator.