Hello Thoma,try to put the system into service mode and try a factory reset.
Here is how to access the service: Information necessary for service can be displayed.
Service mode setting:
1. Turn the power off.
2. Press the [5] [9] and button simultaneously for 5 seconds, then "70 RET" is displayed on FL.
3. Press the [ ] button to select until "80 SRV" is displayed on FL.
4. Press the [OK] button.
5. It is displayed on FL as "Welcome-->SERV".: It is shown to have entered the service mode.
6. The command is transmitted by attached remote control.
Remote Control:
[R] =
[Y] = [YELLOW]
=
Method of making clear service mode: Press the power button (power off).
The display of information to each command is as follows.
NOTE:
Do not use it excluding the designated command.