Hi Erwin and welcome to JustAnswer,Thank you for the question and your patience. Should you still need assistance for information purposes only...Initially, proposed preliminary test (if have not been done); determine if the viewfinder would display previously recorded videos and/or at least the indicators such as the tape counter, Date/Time and others:
Either of the above would require that the unit be opened up for visual inspection, voltage/continuity/resistance checks, confirm faults and effect repairs.
Are you then considering a DIY (do-it-yourself) repair approach? If yes, do you have access to and familiar with a multi-meter and even perhaps a soldering iron?