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Check and replace damaged component/s at its horizontal scan output section circuit. Check the LOT (Line Output Transformer) too for damage. Replace the horizontal scan output transistor. Check the input voltage to LOT. If the voltage is absent check the feeder resistor; if any. If you wish to get some details; check the site linked here. Pull up older posts. http://electronicshelponline.blogspot.com/
Type in this key phrase " my service table today " in the search box at the top right of the display window of the home page, to get gathered some pages which has the details of practical experiences to the author of that site.
Check and replace all electrolytic capacitors in the vertical output section circuit. There will be 5 or 6 of them to replace. Replace all at one time. The fault you describes here is technically known as 'vertical retrace lines'. Visit the site named 'Electro-help' for
more details. Click this link. View it in
'Flip card' option, which can be selected from the drop down box
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are more than 990 posts to different brand TVs now. Sometimes, you might get some more details from there.
if you are using a cable box .. then disconnect everything that is feeding signals into the tv ... then get a signal from some other source (like off the air antenna or video camera) ... if the tv still has the dark lines then you have a bad primary filter capacitor in its power supply .. if it works ok off the air and only does it when the cable box is hooked up .. then the cable box has an open primary filter capacitor . ... the dark horizontal bars you see is ripple from the rectified AC power that is not properly filtered ... if the TVs verticle scan rate is 60 hz and the full wave rectified AC amounts to 120 hz ripple then you will see two dark bars across the picture ... since the two signals are not syncronized then they will slip in phase with respect to each other .. thus the constantly moving pattern ..
Not too many things you can do without an understanding of the circuitry in a CRT TV but there is a good chance that the failure has occurred in the high voltage area and a few things need to be measured there to find which of them has failed.
Catastrophic failure of the CRT (picture tube) are rare anymore but do happen now and then.
If the flyback (horizontal output transformer) has bitten the dust, they are becoming hard to find and much more expensive than 10 years ago.
Additionally, those don't normally fail alone but are killed by or kill, other components, which also need to be verified before replacing anything.
Even with the HV section dead, there are lethal voltages present inside when turned on and not always in places that look dangerous.
sarge, it sounds like the vertical output IC went bad on you. If it was a bad connection or a bad capacitor, your picture would have been a straght line across the screen. They call the output section of the IC a push-pull type of amp, so the top half of the sweep IC went out. If you have had some soldering experience, and or experience with solid state repair, locating the bad IC and replacing it is no big deal. If you havent, stay safe and call in a pro to assist you in this repair, as there is alot of high voltage inside this puppy that is still present even if the set is unplugged. It should not cost an arm or a leg to repair this set. An honest repair on a set like this if you take it in should not exced 125 to 150 bucks. Good Luck
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