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How to Smell Your TV Troubles
January 1965 Popular Mechanics

August 1937 Popular Mechanics
August 1937 Popular Mechanics - RF Cafe[Table of Contents]

Wax nostalgic about and learn from the history of early mechanics and electronics. See articles from Popular Mechanics, published continuously since 1902. All copyrights hereby acknowledged.

Peanuts Comic Snoopy Nose Knows - RF CafeAlthough I have never experienced it myself, I have it on good authority (Mac MacGregor) that the odor which emanates from a burned up selenium rectifier is very foul. Those were the first form of "tubeless" rectifiers. Legend has it that TV and radio repairmen could sometimes smell the burnt up rectifier in a high voltage circuit upon walking into a house on a service call. My own troubleshooting methodology for anything electrical - circuit board, motor, even cables and connections - consists of a careful visual and smell test. Unless very high current is involved, there usually is not a failure betraying hint of either type on today's low power products. Often when the ballast of an old commercial fluorescent light fixture fails, it sends out a nasty hot tar smell. A couple times a year back in elementary, junior high, and high school (1960s-1970s) that odor would permeate the classroom and hallway. Although this article from a 1965 issue of Popular Mechanics magazine specifically refers to TVs, the same principle goes for any malfunctioning electronic device. I remembered and found the Peanuts comic shown in the thumbnail where Snoopy declares regarding the suitability of his dinner, "The eye can be deceived, but the nose knows." That is pretty much universally true.

How to Smell Your TV Troubles

How to Smell Your TV Troubles, January 1965 Popular Mechanics - RF Cafe

The smell of rotten eggs, ozone, burning rubber or hot wax are clues to specific TV ailments. Here's what they can mean.

By Art Margolis

If and when your TV starts acting up and gives off an odor, it becomes rather easy to smell down the source of trouble. Your sniffing sense becomes a valuable piece of test equipment to help you detect the bad component.

There are only a few parts of electronic gear that can burn. Each gives off its own distinctive aroma. They are resistors, transformers, coils and rectifiers. Let's go through the various scents and note the servicing moves that are indicated.

Resistors a la Fricassee

From an electrical point of view, a dressed chicken ready for the oven is a fat juicy resistor with a value of about 100,000 ohms. Current can cook this chicken to a turn.

Resistors must be cooked, they do not burn of their own accord. While excessive current is being pumped through them they produce acrid smoke and a distinct aroma of carbon, wire, insulation and paint. As soon as the current is turned off the fire, smoke and smell stops. Never just replace a burnt resistor. You must find out why it burned or the new one will go up in smoke too.

When your TV starts acting up and gives off a white smoke that can be suffocating but almost odorless it's a resistor burning.

Turn off and disconnect the set. Then determine the approximate area of the chassis that the smoke originated from. Now start a close examination under good light looking for some charred remains.

Slight charring blackens the resistor and ruins the gaily painted colors that designate its value. Extensive burning blackens the area around the resistor and can even cause the resistor to break in half, leaving two stubs. Once you find a burnt one, look around it and follow up the attached wiring. You may find a second and even a third in the same circuit.

Ozone aroma is at the picture tube high-voltage connector - RF Cafe

Prime source of ozone aroma is at the picture tube high-voltage connector. Wipe the tube glass clean and spray carefully with anti-corona dope.

Plastic electrical tape around an old high-voltage wire - RF Cafe

A couple of turns of plastic electrical tape around an old high-voltage wire will stop arcing without requiring replacement of the worn length of wire.

Selenium rectifiers that smell like rotten eggs - RF Cafe

Here's a pair of selenium rectifiers that smell like rotten eggs when shorted. If only one is bad, its still best to replace both at the same time.

Ozone odor is generated when high voltage sparks across on air space - RF Cafe

Ozone odor is generated when high voltage sparks across on air space. Here we intentionally draw on arc from high-voltage tube anode to ground.

Once located, you have to determine whether the resistor is burning because it is defective or because some other nearby component has given up the ghost.

This is done by elimination. Check the junctions where the two ends of the charred resistor are attached. There will be other parts also attached. Follow the wires and see if any of them lead to a tube socket. Then pull out any such indicated tube and turn the set on again. If the burning has stopped, the tube is bad. If the smoke continues the tube is good.

Now trace out any capacitors that are in the line. Disconnect one end of any suspect and turn the TV on again. No more smoke indicates the capacitor is bad. Replace the bad tube or capacitor and the burnt resistor. In the majority of cases the set will work now.

If it doesn't, the trouble is in the minority realm of tricky jobs and further troubleshooting requires more than smell or sight to solve. This is the point where you should decide to call for more skilled help.

Toasted Transformers

When a transformer begins incinerating, it gives off a white smoke and a distinctive odor of burning rubber, insulation and molten wax. Sometimes there is a crackling, frying sound. Once you get the smoke signal, turning off the set will not put a complete stop to it. The smoke, smell, and sound will persist for a while.

Locating the bad transformer requires the use of your hands and eyes. First see if you can spot the source of the smoke. In a TV it could be the power transformer, audio output transformer, vertical sweep transformer or perhaps the yoke. Once you think you know which one it is, touch it tenderly with your hand and feel for heat. A bad transformer will be too hot to hold immediately after you turn off the power. All transformers run a little warm, but should never be too hot to touch.

Once you have discovered the culprit the next step is replacement. As a safety measure always replace the tubes associated with the transformer too. If it's a power transformer, replace the low-voltage rectifier. If it's an audio output transformer, replace the audio output tube.

In the rare event that the new replacement also starts to overheat, smell alone won't effect the cure, and more skilled techniques are going to be required. Fortunately this won't happen very often.

When High Voltage Fries

The characteristic smell of high-voltage burning is a distinct ozone odor like the smell after a lightning storm. It tells you to look for trouble in the high-voltage section of the set.

If you smell ozone, darken the room and visually examine the high-voltage area with the TV on, looking for the fireworks. The ozone producer will appear as arcing accompanied by punctuated snaps or corona heard as sizzling and giving off a bluish ray.

Mild corona is usually just an insulation problem. Aging insulation permits the 20,000 volts to leak out into the air. If the origin is a wire, take some high-voltage plastic tape and reinsulate the area.

If the coil or transformer is the trouble spot, use high-voltage dope or anti-corona spray to coat the bad spot. Apply several layers, allowing each coat to dry completely before applying the next one.

Arcing is different and usually occurs in either the filament wires to the high-voltage rectifier or the high-voltage lead to the picture tube. An effective repair requires replacing the defective wire. Make sure you use high-voltage cable specifically designed for this job. It can be obtained from most electronic supply houses. If this wire is not available locally order from one of the mail-order electronics firms.

If you do any soldering in the high-voltage section, be sure that all points are rounded. A pointed joint discharges high voltage easier than a rounded one.

Any other high-voltage problem is not one to be handled by the amateur and should be referred to a skilled service technician.

Rectifier Stench

Should your TV suddenly give off the aroma of rotten eggs, you have a clear cut repair in most cases. This odor appears when selenium rectifiers go bad. In a TV it is accompanied by loss of picture and sound although the tubes stay lit. Sometimes the set will continue playing or the picture might shrink in on the sides. At any rate, replacement of the rectifiers will put a stop to the odor and the symptoms.

The repair techniques discussed in this article often require working with the TV chassis out of the cabinet. When working this way be careful. Do not bang against or scratch the picture tube. Be sure the set is turned off and the line cord unplugged from the wall before poking around under the chassis with your fingers. And most of all, keep all children away from the work area and if possible out of the room.

Be sure that the set has been disconnected - RF Cafe

Soldering gun makes rapid ports replacement.
Before doing any soldering, however, be sure
that the set has been disconnected at the
a.c. wall outlet.

 

 

 

Posted December 6, 2023

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    Kirt Blattenberger,

    BSEE - KB3UON

RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The World Wide Web (Internet) was largely an unknown entity at the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps while tying up your telephone line, and a nice lady's voice announced "You've Got Mail" when a new message arrived...

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