iPhone 4 flash not working, even after camera replacement

Hi,

I have an iPhone 4 with a non working flash, I thought I'd be able to fix this by replacing the camera, but it turns out this didn't fix it.

The camera itself works fine, and in another iPhone the flash works fine as well!

My best guess is that there is some sort of fault in the connection of the flash on the logicboard... does anyone have experience with this and know how to fix this?

Thanks in advance.

Fabian