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Check the screen voltage. Adjust it to a little lower and check. Check the supply voltage to its video output stage [CRT base card]. If this voltage is less than normal, this kind of fault can occur. Check the smoothing capacitor [the electrolytic capacitor of low capacitance value] is bad. If it is bad, the voltage stated above will go low,and the retrace lines will be visible. Check these.
The fault you now see is technically called vertical retrace lines with picture. The above said are the main causes for this.
If you wish to get some details; check the site linked here. Viewing it in "Mosaic" will make surf easy. Surf the site with patience. http://electronicshelponline.blogspot.com/ Pull up older posts.
Vertical retrace lines is the problem. Thin white lines runs across the entire screen, at about an inch apart to each other. Check its video output supply voltage. Reduce the screen voltage to a little bit down and check. If you still wish to know more about this fault, check this site. Pull up older posts there.
if retrace lines at top of picture the issue is in the vertical circuit--usually a bad filter cap and or the output chip (most of the caps that cause that are 220 uf or 330 uf and connected directly to one pin on the chip.
If retrace lines are across entire screen---likely the master screen control on the Flyback is set too high--causes excessive brightness and the retrace lines.
This fault can occur to mainly three reasons. ABL circuit failure. Low screen voltage or lack of emission from picture tube cathode. Just advance the screen voltage to a little, and observe the result. Screen control can be located on its Line Output Transformer [LOT]. there will be two variable controls built on to LOT marked as screen and focus. Screen control will be at lower side, and focus will bw on the top. Just advance [clockwise movemnt] to a little, not more, advance it till retrace lines are just visible on the screen. Before doing this, set all the picture controls, contrast, colour and brightness of the TV to zero. Once the retrace lines[thin horozontal white lines across the entire screen at about 1 inch distance with each other]; are visible, stop there, turn the screen control counterclockwise to just a point when these lines are just goes off. make this adjustment in a dark room so that you can set this point very correct. After this check the perfomance of the picture. If this does not help you, ABL circuit should be checked for any fault.
If emission of the picture tube has got down, even the screen adjustment said above won't help you. The only way is to replace the picture tube with same type and number. OK.
You have stated that your TV has a lot of horizontal lines before it went off picture. We say that lines as retrace lines. So many of them will there on the entire screen, at about one inch or so apart, horizontaly scattered along with picuture. At that time, you may be unable to down the brightness control also. Even though you have reduced the brightness control to zero position, there will be some brightness level on the screen. You should have to repair that fault at the begining. There is a voltage going to the picture tube base, known as screen voltage. That voltage determine the emission of the picture tube, and we call it a bias voltage. When it goes higher than normal, this trouble ie retrace lines will occur. In long run it may spoil the picture tube itself. I don't know what the case of yours.
Anyway it is best for you to consult an experience technician in this case. Ok.
If you feel good about opening your set then you can try this: Look for the flyback (high voltage) transformer, with the thick red wire which goes to the top of the picture tube. There are 2 controls on the flyback transformer, focus (top) and screen (bottom)Turn the brightness and contrast all the way down and then increase the screen control until you see retrace lines, and then back it down until those lines just vanish. Return the brightness and contrast to normal and adjust the focus control, if necessary, for a nice sharp picture. Let me know if that brings your brightness back.
sound like the screen control on the flyback is set just a little too high. the flyback has the red wire attached to the tube. the flyback has 2 small adjustable controls. if you look close enough 1 is marked focus & on is screen. turn the screen slightly to the left & look at your picture. the screen is like a master brightness & if it's up too high you will see what is called retrace lines.