| MadSci Network: Engineering |
Great question Lee!
The exact lifetime of a television varies substantially. TV failure is caused by several factors:
Fundamentally, the one component of modern, solid state televisions which will eventually fail after time is the picture tube. What usually happens is that the cathodes in the electron gun become weak and produce fewer electrons making the picture appear dim. This can be remedied somewhat by increasing heater temperature, but eventually the oxides coating the cathodes will no longer produce sufficient electrons. Picture tubes have a typical MTBF of anywhere between 40,000 to 80,000 hours. If a TV is operated continuously, a picture tube can last five to ten years. Most sets will operate less than eight hour a day, at this rate a picture tube should last at least ten years.
Ten years is a long time, long enough for other components inside the TV to fail. The semiconductors, passive components, and connections can theoretically last forever. Their life can be shortened by poor design, harsh environments, and poor handling. Older television sets used a lot of moving parts like turret tuners (the channel selector dial). Moving parts tend to wear on each other and don't handle physical shock well. The turret tuner was eventually replaced by all electronic tuning with no moving parts. I don't think you can buy a TV today with mechanical tuning.
Electronic circuits are designed to operate within certain temperature and power extremes. Commercial engineering practices dictate satisactory operation between 0 to 50 degrees Celsius (32 to 122 degress F). Most TV manufacturers expect that your house won't get that hot or cold, so they choose components and design techniques which cut corners and reduce cost. What this means is that if you operate a cheap TV in hot environment for a long time, it is likely that some of the high power components will overheat and fail.
There are other places where TV manufacturers try to reduce cost which may result in shorter life. Electrolytic capacitors fail if they are operated near or above their voltage ratings. Low grade electrolytics tend to overheat and leak. In some cases, manufacturers have been known to remove components until only the bare minimum are present. This was known as "Muntzing". Years ago, Earl Muntz built inexpensive televisions by snipping "unecessary" components. He was reputed to snip components from engineering prototypes until a set stopped working, at which point the component was replaced. This results in a cheap set, but it may not last.
Modern sets tend to be better designed because their parts count has been reduced dramatically. Integrated circuits have squeezed hundreds of analog circuits into small, well characterized silicon chips. Designs for TVs have been distilled down to a small collection of ICs which are commonly used. Even with good design and quality components, one of the most common failures is due to poor connections. Hand soldered connections often yield "cold" solder joints which fail after years of oxidation and temperature cycling. Automated wave soldering techniques have improved solder joints considerably. After solder joints, connectors still remain. High humidity and temperature cycling can cause oxidation on connector contacts resulting in poor connections. High quality connectors are gold plated to avoid oxidation, but you probably won't find gold plating in cheap sets. Dust and other particulates in the air can also end up causing poor connections.
The bottom line is that reliability of television sets has improved to the point that you will want a new one before the old one fails. TVs have become a commodity item competing on features and appearance rather than quality. My parents purchased a Zenith TV in 1976 which only failed after it was moved into a new house 14 years later. I think if it wasn't moved, it might still work today.
If you have any more questions on TV or receivers in general, feel free to contact me at madhu@madhu.com.
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