Hello,
Thanks for the comments regarding the site and forum...glad you find it useful.
You are lucky as i have just got in from work today!!
Firsly, changing the default transponder does ont make channels reappear.
As mentioned on the main site, changing the default transponder frequency only helps the digibox boot up when the main default transponder, 11778, is at its weakest (around 4 to 6pm) or unavailable (depends on your location and dish size!)
Hallmark (and around 30 other channels like Eurosport2, some sky movie channels) is also on a similar frequency that may be unavailable during the afternoon.
And if you cannot get BBC or ITVs then this more than likely down to movement of the dish, or something obscuring the signal (trees, wasp / spiders inside the LNB), the latter you can check yourself...being very careful not to disturb or move the LNB.
Hope this helps...
PS : If you are in my area and my very very full diary allows me, I can always pop around for a service call!
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