NotTaR of Television Sets : About instant-on TVs                    
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About instant-on TVs

Most TVs built since, say, 1980 have only the microcontroller powered from a small transformer when the set is off. This permits the remote control or front panel pushbutton to switch the set on. This circuitry should be no more prone to catastrophic failure than what is in a VCR or digital clock.

Historically, there were 'instant on' TVs which kept a substantial portion of their circuitry live all the time - especially those using vacuum tubes in at least part of the circuitry (other than the CRT). In these, there was a lot more to fail. Those tubes would continue to change their characteristics for many minutes when warming up. Circuits were also much more touchy - remember all that constant tweaking! Thus, it made sense from the users's perspective to eliminate the warmup period and keep those tubes toasty all the time.

In modern solid state TVs, the only component to really need a warmup period is the CRT. All this means is that you have to wait 20 seconds for the picture to appear.