Picture keeps getting smaller and smaller until it is about half

Unless it is a loose solder connection, it is probably not worth fixing.

i dont have a solution but would be keen to find one as mine is doing the same

That is correct. Sony has extended their warranty on panels for this model until Oct. 31st 2012. Just give Sony a call or simply take your set to an authorized service center and you will get your set fixed for free.

DLP projection tvs are bulky and have a design flaw in the convergence board the 2 STK convergence ICS alway dies constinely require replacement,if u use about 4 or 5 hours day in and day out.If the old Mitsubishi tv several years since is was repair,u use it alot?If yes,it time to retire it,and buy the refurbish Plama tv.Not,than get the old tv repair.U Know how to solders?Tries Websites Tv repair World.com,Tvrepairkits.com to buy a convergence kit to repair it ur self.U can go to You Tube type in Convergence problems will see a tutoring video in repairing 2 STK Convergence ICS.

Cost for repair and the part isn't worth it old chap, especially when the holidays are coming around the corner and retailers are hurting for business.  Why not get a lighter LCD or plasma tele with better 1080 resolution then stress over trying to save this old dog? Off to the heap with it is what I say.
Cheers

yes there is a fuse on the bottom left ( think that is whewre it is on this model) but as its near the HT it might be better to let the techs go there If they get eloectrocuted you just call an ambulance If you get fried someone may not find you for a wekk or two good luck

do you have and big sound system if you do the move them away from youur tv. or you sould just bring it to a shop it must be the picture tube

TV's over all have a life span of 10 to 15 yrs, sounds like a problem with the picture tubes, could be biasing or the one of the tube their self''s.

Model VS-45501A  probably not worth fixing at around 400.00
for a convergence circuit overhaul......T.

What is the make and model number? The symptom you are describing is very common on Mitsubishi projection sets, but since you did not say what kind of TV you have, I cannot tell you what is wrong yet.