My Matsui DTR2 does not pick up any channels when tunning it?

My Matsui DTR2 does not find any channels when I try to tune it. It just says "check your Aerial"...
There is nothing wrong with the antenna /signal strenght, I have tested it with another Matsui-box and the other one functioned ok.

I guess it's the small box on the inside that's the problem ??
(I don't know the name of it, but it is the small box that's connected to the antenna on the inside.)

But what can I do about it?
Thank you for any good suggestions!