I get blocks and black screens when watching dvb-t, Digitenne in the Netherlands. This appears both on the free-to-air as the decoded channels, with a KPN smart card installed.
I have a 32FPL3517H/12, production date may 2012.

If I use an external KPN Digitenne tuner and connect via the scart cable, there is no problem. This external tuner has an antenna qualifier, indicating the full 100%.
I have installed an amplified active outside antenna, pointed to the broadcast location.
How can I qualify and/or improve dvb-t reception via the antenna input?