If it's only the TV3, 4 mux you can't tune then it must be a setup problem. Most likely lack of signal strength on only that Mux.
Check your antenna. Which Tx site are you pointing at? Do you have a UHF antenna and the correct polarity?
What are the signal strengths you are getting on each Mux?? Can you confirm you are receiving other channels TV1, 2 Prime) including all the analogue channels?
I have noticed dropouts here on the North Shore over the last few days particularly on Prime. No apparent reason as my signals are 100/100.
Sorry I don't know what Tx site it is pointing at. How can I tell?
I don't know if my UHF aerial has the correct polarity, what should it be?
I can confirm I receive all TVNZ channels 5/6 bars. Prime is 3 bars but is always clear and isn't jerky (all the Chinese stations I pick up are same). Maori TV is the only channel that is jerky and sits on 2-3 bars.
I know this isn't a software issue as the TV this aerial is also used by (obviously not at the same time as my computer) no longer picks up Mediaworks channels either. So you must be right that its something to do with aerial. Could it have been blown by the wind or something?
Here is my aerial. It's pointing West. Do you think it looks too vertical?
Or is it more likely the plugs are faulty?