Getting Started to Repair Your TV Set - The Ins and Outs

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.


Soldering Tips and Part Replacement

is an expertise that is a learned skill. I must warn you that the lead in solder is known to cause birth defects. When soldering or handling printed circuit boards, avoid unprotected skin contact with the solder surfaces. Also, while soldering, try not to inhale any solder fumes or smoke. Most electronic distributors have a battery powered air filter available just for this purpose.

General soldering techniques:

  • Use a grounded tip, low wattage soldering iron with the right size tip and shape so it will maintain a tip temperature of between 500° to 600° Fahrenheit.
  • Use the proper gauge of rosin core solder composed of 60 parts tin and 40 parts lead.
  • Keep the soldering iron tip clean and well tinned.

Proper soldering techniques.

  • Make sure you do not rush the soldering iron heat up time, as the proper temperature is paramount and must be met first.
  • Hold the soldering iron tip and solder against the component lead until the solder melts.
  • Quickly move the soldering iron tip to the junction of the printed circuit board foil and the component lead, and hold it there only long enough for the solder to melt and flow around both the component lead and printed circuit board foil.
  • Work quickly to avoid overheating the circuit board foil or component.
  • Closely inspect your work, and remove any solder bridges with solder braid wick or a static free solder sucker.
  • The solder connection should look shiny and clean, with no brown rosin left behind from the solder, as this can cause ring cracks or a bad connection down the road.
  • Use a small wire brush to clean the printed circuit board and a small spray of non-static, non-residue printed circuit board cleaner.

Unsoldering techniques:

  • Touch the soldering iron to the component lead and the printed circuit board landing until the solder melts completely.
  • Quickly draw away the excessive solder away from the component lead and the solder pad on the printed circuit board with an anti-static suction type solder removal device or solder wick braid.

When unsoldering regular types of IC’s, bend the leads to stand up straight at the same time you heat up the solder on the pad and are removing the flowing solder with the solder wick or solder sucker. When you are taking out a bad transistor, diodes and/or resistors, clip the leads of the component as close to the component body as possible, use a pair of needle noise pliers to grab on to the leads, and heat up the solder to let the cut lead easily come out. Then simply remove the excessive solder.

Some techs will use the remaining leads of the old components as an attachment point for the new component by wrapping the leads of the new components around the old leads and solder those together. In a case as this, double-check the underside of the component leads for a solid good connection. If it looks lose, resolder the connection.

Most surface mounted components are affixed to the printed circuit board with glue. Be careful not to break or damage any foil traces under the components or at the leads of the components while removing. Usually applying heat to the components for a short time while twisting with tweezers will break it loose from the board.

  • Chip components must be replaced with identical parts due to critical foil trace spacing.
  • If there are holes under a chip resistor or capacitor, it may be limited to using a 1/8 watt type device.

Chip resistors have a three digit numerical code on them. The first two numbers is the resistance, the third number is the multiplier. If a small chip resistor had a 473 on it, the value would be a 47K, or 47,000 ohms. Chip capacitors generally do not have any values marked on them, and must be identified by the package they come in or from the capacitor designation in the schematic diagram. Chip transistors are identified by a two-letter code. The first letter indicated the type of transistor, and the second letter indicates the grade of that transistor. The manufacture service manual should always be used to properly identify the proper chip components to replace.

Component removal:

  • Use solder wick to remove solder from the end caps or terminals of the Component.
  • Without pulling up on the component, carefully twist the component with tweezers to break the adhesive bond between the component and the printed circuit board.
  • Do not re-use removed surface mounted components, as they are subject to stress cracking, and can cause tons of intermittent problems.

Chip component reinstallation:

  • Put a small amount of solder on the solder pads on the board.
  • Hold the chip component against the soldering pads with small tweezers, and apply heat to the pads until the solder melts and flows around the end caps or component leads. Do not hold heat to the pads for more then 3 seconds.
  • Always, when resoldering any solder connection, double check your work, and with chip components, use a small magnifying glass to look carefully at the pads.

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