1. No magnets

The N900 case contains two magnets. One in the battery cover, under the kick stand. This fulfills two functions. One, it holds the kick stand closed but most importantly two, it activates a sensor that mounts the SD card when the battery cover is closed and automatically unmouts it when the cover is removed.

This magnet was missing, which mean my phone was no longer detecting the SD card.

The solution was simple: cut a small piece from the flexible magnetic sheet recovered from an old fridge magnet and gue it in the recess under the kick stand as per the next picture (please excuse the quality).



As you can see, I have glued two magnets, one in the kick stand itself, to stick to the magnet under the kick stand to keep it in place when closed (the original housing has a small piece of metal there for the same reason). This had a negligible effect: the magnets are too weak for that purpose, although strong enough to activate the sensor.

The original housing contains another magnet, under the screen. This one activates another sensor that detects that the screen is open (also sometimes referred to as keyboard open). Needless to say, this magnet was missing too, meaning my phone was not registering opening the keyboard. If turning the keyboard lights were the only effect, then I could live with it, but Nokia in their infinite wisdom decided that the on-screen keyboard to enter special characters works only if this sensor is activated. So I could type, only not special characters. So I had to fix that.

Unfortunately, I did not take a picture of the fix, and disassembling the screen to take it later was too much hassle, so I can only sho you the approximate position of this second magnet:



Sadly, using another piece of a flexible fridge magnet was not good enough. It was strong enough to activate the sensor but, for some reason, the sensor is actually about 1mm over the edge of the screen, which means the screen flickered on while opening and then back off when fully open. Pushing the screen about 1mm back activated the switch again but this was clearly not practical. So I had to reuse the magnet from the original housing which is much stronger and works at a greater distance.