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Motorhome LNB and Satellite Dish check

My TV screen , which is connected to freeview reciever DishTV S8100-ZA, says "signal not detected, check cable and dish". The Inline Satellite meter seems to detect signal (noise and indicator increases as dish turns). Checked cables, seem OK. TV and reciever work fine. Using HDMI lead DishTV to TV (HDMI imput source selected on TV). Am at a loss. So maybe the LNB needs replacing/checking. Unit is on roof of motorhome (ladders supplied) so can deliver/drive to your office home or workshop at anytime day or evening. Any thoughts why