The most common problem when a WVR7100 won't lock to an HD signal is that the loopthrough connector on the rear of the instrument has not been terminated. Check the SDI input on the back of the WVR7100 and confirm that there is a 75-ohm terminator on the second input BNC. Mis-terminated SDI signals can be very difficult to identify. Due to the nature of digital signals you will not see the tell-tale brightness increase or flaring that is common of non-terminated analog signals. Furthermore, improper termination often does not cause SD signals to fail due to their slower bitrates but HD signals do not handle the reflections nearly as well.