unplug the box hold up button then plug in wait till display says diag and then search through the tech pages for uhf channel. (DO NOT ALTER ANY OUTHER SETTINGS ) also make shure your viewing the box via scart lead when in the tech menus. good luck
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quick note the 4200DVB STB requires up button to be pressed when powering up. the older di1000t requires up and down buttons to be pressed when powering up 