Most probably it is cheaper to just buy a working n900.

The realfix is to replace the defect ic (most propably gazzo). (chip cost around 2-3$)
If you dont find that chip, a more expensive reball.
You may get away with a reflow.

Anyway you need to heat your n900.
But preparing the n900 to do so includes disassemble the hole device, removing shielding, partly removing the white keyboard foil and the camera module. This takes some time and need some "homemade" special tools to lift the camera.

I always wanted to make a video of a successful repair.

But what means "succesful"?
You applied heat to the right part. The error is hopefully gone.

Now you need to just check that you dont broke any of the "million" functions the n900 has. Which includes that you dont build a wrong solder bridge and your n900 now has half of battery life. Or you applied too much heat and damaged a part of a chip.
That is hard to check.

So it is work, you cant guarantee that it works and in this case internationally shipping makes it too expensive.

If you have a defect device in europe and want to help me make that video.
I may be interested in buying a defect one at 20 euro
And if it worked and you want it back, i can sell it back "repaired" at 20 euro plus shipping cost to you.
But it must have a reliably all telephony functions error.