Thanks again vi_.

With regards to checking the ribbon cable myself - what's the degree of difficulty? Is it a four-screw job or a 300-screw job?

Taking it back to the shop is more of a hassle than you would think. It involves first telephoning a special department from my phone provider, getting various authorisation codes, then dropping it into a storefront that is just a mailbox for the repair, then getting a phone call from the repairer and okaying any repairs, then getting it back... somehow seemingly designed to make it as tedious as possible.

So if it is not a really hard job I'll just try researing the ribbon cable myself, otherwise I will have to go through the whole rigmarole.