More digging - seen this teardown of a Bravia set and the label is very informative:

http://www.fullhd.gr/2008-03-14-21-37-34/teardown/7547-sony-bravia-kdl-46ex720-teardown.html

DBEF stands for dual-brightness enhancement film and it basically sits in the panel to reflect light that's polarised one way, but pass light polarised another.

I believe that it's this film that we can see when the screens fail and that the failure is due to the film touching another layer in the panel.

Still researching!

I think this pdf document from a commercial repairer of LCD panels seals the cause:

http://www.febalcdrepair.com/UserFiles/file/febalcdrepair.pdf

The relevant part is the last paragraph of the first section "Polarizer Film Replacement"

Hello colinmabey

Read skipton01's posts, he has a background in this sort of thing.

Hi,

Noticed a few of you are contacting Watchdog...has anyone got the link? Many thanks.

As I said in a previous post, neither Sony nor Comet are interested and in fact Sony have stated that they know of know issue of this kind with this TV?!!!!

Well done Skipton on your research!

Just found this thread and thought I was on my own with this fault.

Can't believe how many others are affected.

Noticed the dark band on the r h edge of the screen a while ago, but it 's def getting worse (and other vertical 'streaks').

Can't imagine I'll get any joy from Sony, but that won't stop me trying.

Also having probs with S380 BD player (fortunately, it's only a month or so old, and bought from Argos), so that's going back.

Won't be buying another TV set from Sony.

OK, so the day for my engineer visit came and went - the engineer never turned up, as apparently their van broke down!  So, that's a days leave to add on to the list of inconveniences.

In frustration, I phoned the SOny customer helpline and got nowhere - they recommended that I take it in to where I bought it - they couldn't understand that the Sony Centre had closed down - that's Cairo call centres for you.

I got back in touch with the support/repair centre again and managed to find out that all Sony service centres had recently had a note to say that all Sonex warranties were being transferred to Sony ones (as goodwill only) and I got the number for the Sonex Extended Warranty Helpline (PM me if you want it).

The number gets you through to Sony, not Sonex and the lady I spoke to there was incredibly helpful - replying to emails promptly and courteously.  All I had to do was scan and email my original shop receipts and warranty card (even though I registered the warranty online) to her and once she had proof of the purchase, her last email said:

"Thanks, I should be able to arrange a repair for you now"

So, fingers crossed, I'll have my duff tv collected next week and inspected, then we'll come to some settlement.  I've already broached the subject of replacement as opposed to repair and indicated that I'd rather be able to pay a little more to get a non-S-LCD panelled unit (for those not aware, pretty much all Sony & Samsung televisions since around 2005 have used LCD panels made by a company called S-LCD Corporation, which is a joint Samsung/Sony enterprise, but has recently been taken over completely by Samsung).  The higher end Sony units use Sharp panels (HX and NX series screens), and I'd prefer to get one of these.

More details later on.

Engineer finally called today - didn't ask to see the issue with the dark lines as he said he was familiar with them, but I demonstrated the problem anyway.

He agreed that it was a panel fault "seen loads of them - yours isn't too bad, but it'll only get worse.  Loads of Sony's affected and not just the cheaper ones too" he said and took the tv away.  This re-inforces that the issue is the same as those affecting the W and X series.

He couldn't say if the panel would be available, but he doubted it would be.  I should know what's been resolved by the end of the week.

So, looks like I'll be bartering with Sony over the replacement model.

Phoned the menders today, as advised, and I was surprised to hear that they're waiting on a new screen panel, which is expected next week!

It was my understanding that a new panel would make for a too expensive repair, as it's normally cheaper to just get a new complete television.

However, I'm not arguing, as the KDL-40V3000 is a decent unit still and I'm not interested in 3D