NighVision sensor

Still trying out my Avantguard4 on the workbench.

The Nightvision sensor does not seem to function. The sensor input always shows red on the input/output screen. Also, the siren never chirps with SilentNight feature On. Tried shining a 50W halogen at it at close range, but this doesn't help. When unhooked the sensor appears fine. It reads some 500k in the dark, up to about 1k in full light. When hooked up, I also measure a small but definite signal at the wires, that changes with the amount of light on the sensor (2 - 20 mV). Changing the lighter/twilight/darker settings didn't help either.

Any thoughts?

This is quite a monologue, but people are viewing it, so another post:

It appears that the bezel of the LDR contains a little filter. After removing it, the edges of the filter, which are obscured by the bezel, are blue, but the center is almost black. I suspect that the filter changed colour over time (I bought a used system). Anybody have any experience with this discolouring, or the sensor changing sensitivity over time?