There are three prongs that hold a dome shape cover together. One of the prong is spring loaded.
Normally, you would push the cover to the direction of the spring loaded prong, then the spring would extend enough and you can take out the cover. However, for this one the prong did not extend enough to slip the cover out. The spring loaded prong moves about 1 cm, but that is not enough for the cover to fall off. I tried to push it very hard, but it still does not extend enough.
Each prong is screwed from the inside, so I cannot take it off.
Is there some special way of taking the cover off?