I've been trying to track down this model, but am finding it a little elusive. Is it a CRT model and are we talking the wonderful world of SCART?

If the answers are yes I would imagine the connections to be something like;

AV1 - RGB/S-Video (Scart on rear)
AV2 - RGB/S-Video (Scart on rear)
AV3 - S-Video/Composite (Scart on rear / S-Video and Phono connectors on front)

If this is the case the input would automatically use whatever the output device is sending; i.e. whilst there may be codes to select a specific AV input, it's more than likely there are no codes to select the type. But then you say the AV2 code does exactly this.

Must confess, I'm puzzled; which is why some info on the TV would be of help.

PS
As a footnote to the above. I've checked the tuner and AV (Video) codes 1-6 and found them to correspond with the info I have. AV (Video) code 7, however, is something of an oddball.

My info gives it as an 8 bit code for widescreen switching. Just wondering if anyone can confirm this.