I have the Sanyo TUHD1010 Freeview HD receiver (from the Warehouse), and have just been having the same problem that Laworder and butlerboy described: TV3 had audio but no picture for several days. All of the other channels (including TV3+1) worked fine, TV3 audio, information and teletext all worked without problem, just no picture (a black screen). Signal strength was 80% and signal quality 97%. No abnormal atmospheric conditions, and the set-top box was connected to a rooftop aerial with a direct line of sight to the TV transmission tower.
I tried retuning (no effect on the missing picture, but gave a 'service upgrade' message when I tuned into TV3 only), updating the software (no update available), and turning the tuner on and off again (no effect).
Eventually, I did what butlerboy reported, and unplugged my tuner at the mains for 30 seconds before restarting - this immediately solved the problem.
This is clearly an issue with the Sanyo TUHD1010 / Draco HDTV5500 tuner - I just want to document the solution for other users (unplug the tuner for 30 seconds, then restart).