I think you're saying it works okay via scart?
It does look as though the tuner in the set is faulty...providing you are tuning it correctly.
I have no idea how much a new tuner is but a company based in Manchester offer an excellent tuner repair service...their repairs are guaranteed and they offer a quick turnaround service to the trade...you can find them
here
You would need to get an experienced engineer to remove/refit the tuner.