Fixed TV that’s no longer working? (4-3)

I believe the answer is:

dead-set

I'm a little stuck... Click here to teach me more about this clue!

'fixed' is the definition.
(I've seen this in another clue)

'tv that's no longer working?' is the wordplay.
I cannot quite understand how this works, but
'tv' could be 'set' (television set) and 'set' is found in the answer.
'no longer working?' could be 'dead' (I've seen this in another clue) and 'dead' is found within the answer.
No letters remain.
This explanation may well be incorrect...

Can you help me to learn more?

I've seen this clue in The Times.

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