I have a Pace DTVA freeview box which, when I received it, would not
find any channels whatsoever. After adjusting a pot on the tuner I was
then able to receive 70 channels. They work fine except for anything on
Multiplex 2 (ITV, C4, E4 etc), which suffer bad breakup.

I just had a new roof aerial installed, and also have a Sony D800 that
works fine on all channels, although it does show Mux2 as being slightly
weaker than others.

So I guess the Pace is being overly sensitive to the signal, any idea if
theres a specific component worn out?