This is a 90's 25 inches tv set model Z25X22S (GX generic chasis) it came with horizontal retrace lines as if G2 screen control would be too high, I checked and it was normal, I changhed the video B+ capacitor and it make no effect, then I checked all video and smps B+ waveforms and all seems to be normal, I really don't know what I'm missing, I know that this is an old tv set but maybe someone of you expirienced guys had have the same problem and know this case, any posible help is really apreciated, thanks.
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Re: zenith tv, video retrace lines.
How is the 200 volt supply to the video output transistors??
measure the collector voltage of the video output transistors with the crt board on and off the crt. if voltage goes up when crt board is off then crt shorted
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Retrace lines. If you wish to get some details; check the site linked here. Pull up older posts. Surf the site with patience. http://electronicshelponline.blogspot.com/
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Most "modern" CRT TVs have automatic color biasing which means a complete of manual control. Depending on how your set is manufactured, it may have a control for each color located on the neck board for adjusting the drive to each of the CRT guns.
What you're seeing is called 'retrace' and you're correct that this has to do with color blanking. The most common issue causing 'faint' retrace is too much drive to one of the CRT guns. Hopefully, your set has an adjustment to back off the drive for the green gun. If not, this can be the result of a bad capacitor or leaky transistor in the green circuit.
If all else fails, locate the SCREEN of G2 knob on the back of the flyback transformer and back it down a touch; sometimes this is all it takes.
Those lines are called vertical retrace lines. They appear when the G2 (screen) voltage is set too high, or when the video amplifier fails or lacks the high voltage supply (200v).
Have you got any electronics experience? You will need a multimeter and soldering skills.
If you do or know someone who does, take the set apart, look at the video amplifier IC (it is on the board at the back of the tube), get its model and download the datasheet. Find the pin that is labeled "high voltage supply" and with the set turned on measure it against the one that says "ground". You should have somewhere between 180-210v there. If that voltage reads zero or a very low value, the amplifier circuit is shorted or the power supply is not working properly. Unsolder the video amplifier and measure again, if the voltage comes up then buy a new amplifier IC, if it doesn't it's time to check the power supply. I believe you can find a service manual easily, follow the directions there.
Safety precautions: Do not under any circumstances touch the leads of any capacitors, and stay away from the big fat wire going to the top of the tube. Do not do anything inside the TV while it is plugged in (except measurements), and always use well-insulated tools. The high voltage section of the TV does not pose any health danger, however the shock it can give you will make you jump back, possibly into something sharp.
This is a problem with the vertical circuit. If you can solder, you should be able to fix this. With teh unit unplugged, open up the back and locate the vetical IC. This should be a small flat IC attached to a heatsink with about 9-11 pins. It may be marked LA7837 or something similar. Try resoldering hte pins. If that fails to resolve the problem, replace the IC. I will look up your specific model and try to get more details.
On the inside of the TV, there will be a knob with a RED cap on it, labeled vertial position. (it actually looks like a variable inductor)
With an allen wrench (possible 1/4) give it a half turn in either direction and see what happens. On the Z25x22S model, the vertical and horizontal position adjustments should be right next to eachother, but on the model i worked on, there was no variable pot for the horizontal position.