We'll the authorised service agent for TC is Real Electronics in Sheffield and they aren't cheap.
They don't repair to component level, just board swappers. There are a number of posts on here about Mark Bass repairs as they are also the agents for them. Generally it's not economic.
Here are their charges from a few years ago when I binned my MB amp as the repair was more than the amp was worth.
£35 to diagnose the problem, which you get back if you go ahead. £69 fixed labour, £18 courier fee to send it back + parts all +VAT.