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From your detailed description, it sounds that the main chroma processor IC has damaged. Raster means nothing, but the lighted screen that appears, when a TV is switched ON. For some brands, there will be a blue screen; when there is no signal input, and some others will have a bright white screen with some snow.
I advice you to contact any service technician, to get this TV repaired. If you wish to get some details; check the site linked here. Viewing it in "Mosaic" or "Magazine" will make surf easy. Pull up older posts. Surf the site with patience. Do a search by type in the brand name of your device at its search box and press "Enter". http://electronicshelponline.blogspot.com/
First make sure that the brightness and contrast are turned up.If the screen is lit up (that is you have a raster) then the problem would be in the video circuits.If the screen is not lit then you have a problem in the deflection circuits.A good possibility,with no raster,would be the Horizontal output amplifier.If you are not familiar with circuitry you would need a tv tech.to do the repair.
check the high voltage with the screen control turned up high where there is no raster. suspect problem within the video circuit where there is no high voltage or defective picture tube.some time when the screen is black and the screen control advanced,you can see if the tv has video or vertical or horizontal problems on the screen.service the high voltage circuit if there is no raster or high voltage is seen.no raster can be caused by the no heater or filament in the CRT.----
a defective picture tube can cause many problems, such as, poor brightness ,missing colors,intermittent picture,poor focus,a single-colored raster,arching in the gun assembly,retrace lines in the picture,negative picture,chassis shutdown,noheater or filament lit and no raster to name a few.an open filament or heater can cause no picture or no raster symptom.a defective CRT can have an extremely bright screen.loose particles of the cathode element can lodge between the grids and cause an intermittent black and white picture. simply tap the ends of the CRT gun assembly and notice if the picture begins to flash off and on.----
with a leaky picture tube after turn on the raster dims and get extremely bright.a dim picture with no green in the raster can result from a bad green assembly. a heater-to-cathode short can cause a raster to change colour or a result in no raster at all.replace the picture tube if there is severe arching in the neck of CRT.
excessive brightness with retrace lines and a vertical collapse to a thin line can be caused by a bad coil on the neck board of the picture tube.rejuvenate the picture tube when there is very bright green screen.
check for the resistance change on the resistors of the CRT neck board for an excessively bright picture with retrace lines.excessive dust inside the CRT spark gaps within the picture tube socket can cause the very bright raster and the chassis shutdown.a defective video amp,luminance buffer,or reference transistor can cause a bright picture with retrace lines.
for getting any required parts to replace you can get it from
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It is not a good idea for electronic products to be in storage for long
periods of time. It is even a more poor idea to purchase used from a
rental center; the result is more often than not a very bad experience.
With no picture, but working sound, it is a loss of the high voltage
system. This is almost always failure of the high voltage
autotransformer called the flyback and/or the HOT (horizontal output
transistor) - which work together in producing the horizontal scan of
the raster system and the high voltage to prduce the raster upon which
the video picture is modulated.
The failure could very well be from HIGH temperature involved with the storage of the tv set.
The repair costs will be over $150 but not more than $300; depending on the exact parts that need replaced.
But: try the hard reset and the vibration/whacking test first to see if the moving business caused failures.
Hard Reset: Unplug for 4 hours, then try again. Do it twice.
You have an intermittant vertical sweep circuit! It could be the vertical out put IC solder connections on the printed circuit board, or maybe the IC itself has poor connections between the IC and the contact legs that mount the IC, or another componet in the vertical sweep circuit. If you know how to solder and unsolder, work on printed circuit boards, then you shoul have no problem replacing the vertical sweep circuit. Good Luck
do you get sound while screen does black? what do you mean by "until eventually it has turned black and will not come back"? is it black from the minute you turn the tv on untill you turn it off? if sound is good but picture is black, it may be the resault of a fried monitor tube, in this case replacement will cost alot.
if sound is dead also, them it is probobly power supply related issue. get out your DMM and measure the voltages in the power supply. When the screen goes black, is there still regulated B+ going to the circuitry? Do you still have HV? Is the filament of the CRT lit? Does the set still have a raster (you may have temporarily increase the screen setting to see it)? Do you measure any of the flyback derived B+ voltages that go to the video processing, tuner, Vertical Deflection, and other circuitry?