I have been giving a lot of advice to a lot more of the "do-it-your-selfers" over the past few months, and have gotten many of the same questions regarding safety procedures and soldering techniques. One of the most important things to remember is that an improperly repaired device can affect the safety and reliability of the product. If you do not feel comfortable performing these repairs, or feel you are not qualified to perform these repairs in a safe manner, please do not risk trying to do so. Seek the assistance of a qualified service technician.

In this article, I will be covering these topics:

• Hot Chassis Warning
• General Service Precautions
• Picture Tube Discharge
• Soldering Tips and Part Replacement

Hot Chassis Warning

The "hot chassis warning" is in every service manual for a very good reason. It reminds techs, as well as beginner technicians, about the dangers of working on A TV set. Some TV receiver chassis are connected electrically directly to one side of the power cord that plugs into the wall. This means that if an electrician or repairperson replaced an electrical outlet, and did not make sure the hot line and the neutral lines were connected properly on the AC socket, a great shock hazard will exist. In today’s modern electrical world, the large slot or the screw color of silver is the neutral line, and the small slot or brass colored screw is the hot line of the socket. To confirm that the AC power plug is inserted correctly:

• With an AC voltmeter, measure between the chassis ground and a known good earth ground, such as a cold water pipe.
  
  
• If the voltage reading is more then 1.0 Volts AC, remove the AC plug from the wall and reverse the polarity of the plug into the wall socket.
  
  
• Remeasure the voltage to confirm that the voltage is less then 1.0 volts AC.
  
  
• If the voltage measures about 85 volts AC between the chassis and a known earth ground, regardless of the plug polarity, do not attempt to service this chassis with out what is called an Isolation Transformer.
  
  
• Some TV chassis have a secondary ground system in addition to the main chassis ground. This secondary ground system is not isolated from the AC power line. An insulating material
  that must not be defeated or altered, as doing so will create a severe shock hazard, separates the two ground systems.

General Service Precautions - Do's and Don'ts.

Always unplug TV’s AC power cord from the wall before:

• Removing or reinstalling any component, printed circuit board, module, or a plug connection.
  
  
• Disconnecting or reconnecting any test equipment leads.
  
  
• Connecting a substitute part in parallel with a suspected bad part.
  
  
• Discharging the picture Tube 2nd Anode lead(s)

Never use a heat sink as a ground connection for your test equipment. You should find the proper chassis ground for this.

Picture Tube Discharge

If you are working on a CRT type projection TV set, you have three picture tubes that should be discharged to prevent accidental shock. You can discharge the picture tube’s anode at any of the R, G, or B outputs on the High Voltage distribution block only by:

• First connecting one end of an insulated clip lead to the ground on the back of the picture tube, or the mounting plate of the picture tube.
  
  
• Then touch the other end of the insulated clip lead to the wire coming out of the High voltage distribution block, or by using a long handled screwdriver, with the clip lead attached and slid up underneath the rubber boot on the picture tube High Voltage connection.

All TV sets that have a picture tube will have a high voltage transformer with a heavy red wire that runs up and connects to the picture tube with a suction cup. Under there is an average of 32,000 volts when the sets on. Even when the set is off, it can hold a large electrical charge. If it zaps or bites you, it can make a grown man cry, and not only that, can stop your heart! Therefore, the point is to never ever stick a screwdriver under the HV cap even if it is unplugged.

If the cap has to be removed, attach one end of a clip lead to the metal exposed strap that is around the picture tube, and the other end to the screwdriver. Without the metal blade of the screwdriver being exposed to you, slide the screwdriver under the cap slowly. There should be a little pop if there is any voltage left. Wait for a second or two, remove the screwdriver, and pinch the top of the cap perpendicular to the wire while pulling up on it. Never pull on the wire. With the cap off, clip the clip lead to the anode connection on the tube while the other end stays on the grounding strap.

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