Sony Wega 70 inch lcd tv has blue cloud on big portion of it?? what needs to be replaced and how sure are you?>

Light Engine needs to be replaced. Encompass Parts 1-800-638-3328

This is avery common problem with Sony LCD rear projectors.You need a new optical block.There was a warranty extension on this model that has since expired,however if you call Sony customer service they may cover a portion or all of the repair.Otherwise optical block is very expensive.

light engine will be the problem

That's OK, I been provided you technical info about TV problem.

Sounds like magnetic interference,Do you have a speaker close to that corner?If so you need to relocate it a little farther away.

Hey there Aleman500-

I had this exact same issue with mine. Started noticing the "blue cloud" on the bottom portion of the screen.

Please follow this link and the instructions listed. I opted for an "upgrade" that was offered (brand new 46" bravia lcd) but sony had also offered to fix my tv for free.

http://esupport.sony.com/US/perl/news-item.pl?mdl=KDF42WE655&news_id=206

Happy New Year!

call Sony. I received a 52 inch lcd replacement for little money. love it

Sony wega blue dot or star pattern on screen
http://esupport.sony.com/perl/news-item.pl?news_id=206&mdl=KDF42WE655
Models: KDF-42WE655, KDF-50WE655, KDF-55WF655, KDF-60WF655, KDF-55XS955, KDF-60XS955, KF-42WE620, and KF-50WE620
Sony LCD Rear Projection TV - Optical Block Problems

Uh Oh! blue screen of death. Your light engine has warped a little from overheating and is distorting the picture.

My suggestion to you is to get on the phone with Sony and start complaining, then keep complaining until they agree to pay for it. Even if it is out of warranty.
You may have to get the problem diagnosed by a pro before they agree to pay for it though.
Hope ya fix it!

It might be just dust somewhere in the light path to the LCD panels or on them. The only other thing that comes to mind is the light engine itself and that is no easy task to replace. The part number for it is A-1084-666-A and can run close to 1000.00 for the part. Can you post a picture of the issue so I can look at it?