No Nav Signal even LED's working

Hi RoviosI'm Tom and I own 3 Rovios. I use them as house guards. So every 2 minutes they bark when we're not at home.Of course we drive around, to look after the rooms from time to time.Since I bought it used from ebay, one Rovio doesn't get a NAV signal from its docking station.I checked the one IR-LED of the vertical arm with my old digital cam. I see it on the display, so this LED is working.The 2 LED inside the lense are also seems to working. I dismounted the bowl of the lens and point the LED towards the sensor of the Rovio.The Nav Signal is then recognized by the Rovio. When I point the 2 LEDs on the sensor, when the lense is mounted, there is no Nav Signal.I'm confused. Of course the lense is clean and I tested the Rovio with the other docking stations, so the Rovio itself works find.The docking station somehow must be faulty.Any idea ?Kind regardsTom