# Analog TV turns on and shuts off before image can be seen



## Jo-Diaz02 (Jul 7, 2009)

Hello, I have a problem with an old TV. It´s a Zenith 27" analogue TV. The problem is that it was stored for about two years and got back in use 5 days ago, it was functioning OK but yesterday was an exception. After watching some TV I turned it off, then a few hours later, I pressed the power button and it turned on but before the image could be seen, it shut itself off and won´t turn on again unless I unplug it from the electrical outlet and plug it again. I was wondering what could be causing this. 

Heres the info:

Make/Brand - Zenith
Model # - B27A34Z
Manufacturing date - August '99
Serial # - 921-4330354

Any help would be great!


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## octaneman (May 13, 2009)

Hi Jo-Diaz02


Being in storage for so long dust has accumulated on the board causing it to overheat. The board has to be thoroughly cleaned and reassembled, after the cleaning is done power it up and see if it happens again.



WARNING ! : T.V's carry a high voltage charge for months even when disconnected from the wall. To prevent serious injury or death the flyback transformer has to be discharged to prevent electric shock. PLEASE DO NOT OPEN THE T.V COVER IF YOU DON'T KNOW WHAT YOU'RE DOING.


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## Jo-Diaz02 (Jul 7, 2009)

´Hello,Octaneman! Thanks for the reply, I should have stated above tat I had laready cleaned the TV´s boards before even plugging it after so much time of inactivity. The T.V. worked for a few days, 3 or 4 dyas, then I turned it of and when I tried to turn it on it turns off. I can hear the relay when it switches on and the screen makes that sound like every other t.v. , it takes 2-3 seconds to start up then it turns itself off, I can even hear the audio of whatever show is on the channel selected but only for a second or less befor it shuts off. 

Then the power button does nothing. If I want to power the t.v. again I have to unplug it and plug it again. I don't know if it's pertinent but I always hear something inside the t.v. sounds like *fwwwuiiiip*,(something like priming) wen I plug it to the electric outlet, always sounds like that since I got it.

Sorry for not being clearer on my explanation on the first post. Any other suggestions?


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## octaneman (May 13, 2009)

What appears to be happening IMHO is that there is a problem on the voltage regulator on the power supply. The relay clicks on but can't sustain the voltage to the horizontal output. The noise you hear when you plug it to the wall is most likely coming from the flyback transformer attempting to power up. To find out if the flyback is working pass your hand along the screen, if you feel static electricity it means the flyback is partially working. 


Question: Is there a thin horozontal line going across your screen ? Or is it completely blank ? 

post back your findings.


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## Jo-Diaz02 (Jul 7, 2009)

There's no line on the screen, it starts to show the image and as soon as the image is about to be displayed the t.v. shuts down. I suspected the reason had to be, as you say, that the relay can't keep "on". The t.v. don't show any lines, it just starts up, the screen keeps the same way as when it is off. Then the image starts to appear on screen and before it can be seen, clearly, puff it shuts off. You know when the t.v. is warming up? when it starts ad you can hear the sound but the image is gradually getting clearer until you can see it, it's like that but in this case, the image never gets to be seen completely, the t.v. shuts off before it gets clearer. But I can see the image is a full one, not a horizontal or scan scan line, if that's what you meant. 

So, should I test the components of the power section of the board? I have limited knowledge since I have only taken a course on basic electronics. But I have fixed like 5 or 7 t.v.s Simple solutions, change some caps and some resistors, nothing more complex than that. What should I do, Octaneman?


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## octaneman (May 13, 2009)

The most important thing when working on t.v's is the safety factor. Since you have already worked on a few t.v's by replacing caps, I'm assuming you are familiar with the dangers involved when working with high voltages. 

When working on your set the primary need will be is getting a wiring diagram to follow traces, without it you are working blind and wound up doing more damage than good. Once you are set up with the diagram, open the cover discharge the flyback transformer. First thing you do is do a visual inspection and check the usual suspects like fuses, burned out components, hot spots etc.. 

Break out your DVOM and start testing the power supply side of the board, start testing caps, the transistor relay driver, and the voltage regulator. If you are familiar with transistors locate the horizontal output ( should be on a heat sink near the flyback transformer) take the number off the component and do an internet search for its datasheet and test it with your meter. On older analogue sets the horizontal output transistor burns out constantly. 


If you have any difficulty with all this then it's best to bring it to a shop.


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