Denon AVR-5700 setup menu MIA

For some reason the receiver fails to output the onscreen setup menu to my monitor tv. The manual states that the signals are output to the "S-VIDEO MONITOR OUT 1" jack, and that is indeed where my cable is inserted, and it's the only video output connection. But I get no onscreen menu when pressing the "system setup" button. Resetting to factory settings had no effect. Has anyone some insight on this? Thanks very much.