Hanging the TV, wall material unclear

How about getting a "locator device" that detects the different materials or their position in the wall? :)

How about getting a "locator device" that detects the different materials or their position in the wall? :)

That would be a bit too expensive for me just to drill four holes, and you basically assume that a wall is free of foreign objects.

Well, you just have limited options: - Looking at blueprints - not available. - Cable/beam detector - too expensive. - Drill/scratch carefully and check.

The much-cited crystal balls are currently as scarce as many other important building materials ;)

First, I would make sure that there really are no cables running here! So a cable locator device would certainly be helpful. I always use mine to simply be "safe" (I once drilled into a power cable - so I know that despite all caution, you can still score a direct hit).

If you have a TV mount with several mounting holes, then you could certainly do without 1 screw. I can only advise you to use proper anchors here that are suitable for your wall (e.g. fischer duopower).