There is a dark patch on my screen and it comes on all the pictures

the bad news is the display is bad 99%

That's called backlight bleed. It's a known issue with certain models of the LED screens. I had a similar issue with my previous laptop, a Lenovo G560. The only solution is to replace the screen.

Shannon, cleaning the mirror or the lens will only drgrade the picture that's reflected onto the screen. A dark picture is most likely caused by the ~300 watt lamp aging and now needs replacement. You can confirm this for yourself by removing the lamp from behind the right hand speaker door and looking at the bulb-shape at the inside, bottom of the reflector. The bulb should be clear, with maybe a small white patch on the top of the inside of the electrod chamber. If it's a large white patch, or the chamber has any black, or even worse has a deformed chamber, the lamp only needs to be replaced.

I did the longevity testing for the 65" TV's. No other component caused the TV to 'darken' as you state....

Is there a dark patch when you see the picture, easiest way to check is on the tv tuner with no cable attached, this way you have a grey static screen, if there is a darkness across the screen when it lights for that breif moment, then it may have a broken backlight tube. Had the same problem with my 32" LG.

Sony TVs has an Optical Block issue. If there is an issue with the optical block, then there will be green, blue patches or tint on the TV display. Try resetting the TV to the factory settings and try Power resetting the TV. Turn Off the TV and remove the power plug from the wall outlet for 1 minute and reconnect it and check the operation. If the issue still persists, then TV may require service. You can contact the Customer relations team and check for the available options. Sony had repaired free of cost for such issues. Hence, contact the customer relations.

that is a factory defect you call the dealer for the warranty.the defective part of your tv is the inverter board.this board supplies high voltage supply to the backlight cold cathode flourescent lamp.This lamp is the one illuminating the screen of the tv..the lamp is installed at the top and bottom of the screen thats why the center of the tv is dark because the lamp does not lit well..tnx

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This is problem of Optic Block (light-engine) that will be replaced and it is costly fix.
Click HERE to get price info and part image.

Replace the video board, if you can find one. Letting it cool down will not help any.

This web link might help u out.

http://esupport.sony.com/US/perl/model-home.pl?mdl=DCRTRV250&LOC=3

Thanks for the picture - that's a big help.
It looks you have the dreaded light tunnel collapse common to all LG DLP TV's. Inside the light engine there is a square tube made up of four mirrors. These mirrors deform and crack with the heat of the lamp. They fall down over the light aperture and cause a shadow of varying degrees. It is fixable now at a realistic price ( used to have to replace engine) as LG have made the parts available. It would take a competent tech around three hours to complete or if you are technically minded you could do it yourself. I hope this helps.
Hope Ya Fix It!