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about television

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magneteens

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HAI FRIENDS,

I AM HAVING ONE DOUBT REGARDING TELEVISION. THERE IS POWER CUT, YOU ARE LEAVING THE TV IN ON CONDITION.ONCE WHEN THE POWER COMES THERE IS PROPBILITY OF LARGE FLUCTUATION IN CURRENT WHICH LEADS TO THE DAMAGE OF PICTURE TUBE.SO HOW TO GET RIDOF FROM THIS.IS ANY CIRCUIT AVAILABLE FOR THIS?

KALAI [/u]
 
You might install a simple double pole relay and pushbutton - in series with the power to your TV. Wire it so that once the button is pushed the coil remains energized - but on power failure the contacts open - requiring that the button be pushed again as a reset of sorts.

I have to wonder if modern TVs come back on again after power failure. I'll have to check mine at home. Not something I ever worry much about.
 
I have seen two tv's that "stay on" after a power interuption, and when the power comes back, they come right on... but that was a very-very old black and white tv and the other was a small countertop model, also old.

all the modern tv's I have or are at my folks place (even their 30 year old mitshubishi) have power failure interuption. once the power goes out, tv's power supply shuts off and won't come back on until you manually turn on the tv. the newer 'digital' controlled tv's must do this with electronics, since their switchs are just momentary inputs on some microcontroller.

the old mitshubishi I think uses the above mentioned switch and relay method... the power switch has to be switched from ON to OFF to ON to restore operation after a power outage.

I wonder about CRT monitors for computers? they seem to be the reverse of a television, with my monitor on here, I can unplug it and plug it back in, and it resumes its "power on" state ... I wonder if they're built with in-rush or soft-start circuitry, to avoid surges.
 
the cct you are decribing as a pre-charge cct and yep more than likely since TV's CRT work at kV levels
 
glmclell said:
I have seen two TV's that "stay on" after a power interuption, and when the power comes back, they come right on... but that was a very-very old black and white tv and the other was a small countertop model, also old.

Ya , thats old alright, as I recall the were "instant on" models. What they did was to keep the filaments in the CRT and the other tubes energized even when the set was off.

Newer TVs and Monitors have smart power supplies that prevent current inrush.
 
There is only an extremely unlikely chance of it damaging the CRT, I wouldn't even bother considering it.

As for the TV coming back on when the mains has been off, there are a number of possibilities:

1) Any 'modern' TV is likely to be remote control, and have a standby option. A 'modern' TV should remember (in EEPROM) the last state it was in, if it was in standby it should come back on in standby, if it was 'on' it should come back 'on'.

2) Older remote control sets had an extra momentrary contact on the on/off switch, when you turn the set on with the mains switch it brings the set out of standby. Following a mains interruption these sets will always revert to standby.

3) Older non-remote sets will simply cme back on when the mains is restored, there was no standby option.

4) A number of the modern 'cheap crap' TV's (usually made in Turkey or Eastern Europe) always come on in standby, even when turned on from the mains switch - so you have to bring them out of stanby, either by the remote, or from a button on the front.
 
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