supply OK, no LED is on

The power supply PCB delivers all voltages as specified.

When the AC-plug is in the socket it appears that the HF-amplifier of the coax-signal is working; because the signal of iets gets better on the VT-set.

But none of the front LEDs is working and there is not any usable signal on the scart plug for the TV-set.

What to do or test next?