I've just seen your post -(been flatout tuning TVs and fixing problems).
One thing we've come across often since the frequency change is that the TV won't pick up one particular mux during the autotune (although it sounds like your not getting any channels at all!), or people can't watch their VCR or DVD since the change.
The reason is that, in the Waikato and BOP, they are now using channels 32, 34 and 36 off Te Aroha, and a lot of VCRs and some DVDs use 34 or 36 as their output channel. So the two signals are now clashing with each other. - bypass the VCR or DVD and do another scan to see if that's the problem.
The output signal of the VCR or DVD will need to be recalibrated to another channel at least two, and preferably four, away from 32, 34, 36, 40 (Central) or 44 (Maori), then the TV will have to be retuned on the analogue channel if you use an RF channel to watch your VCR. - If you watch the VCR through AV or component then obviously you wont have to retune the TV.
- Hope that helps someone.