Rear camera and Flash issue (logic board)

Hey guys,

Keep in mind, I am new to IPhone repair. Everything I say in the following text is what I think could or could not be the issue to my problem, please do correct me if im wrong.

I have the following problem with my device:

My Rear camera does not work.

When I open the camera application the rear camera stays completely black, when switching to the front camera there is no issue. When I switch back to the rear camera again its still black and gives me a pop up saying: The iPhone needs to cool down before you can use the flash. In the top left corner of the screen I get a yellow triangular sign with an exclamation mark.

I think I can exclude the following things:

It is not software related, I have iTunes restored my device, I have also tried downgrading to a previous update version.

It is not the camera itself

I have replaced the camera with multiple different cameras, I have used a known working camera on it from another device.

I have used a known working (complete) different device and changed only the Logic board. (one logic board had no issues and the other still had no working camera)

I did some research and i think that it could be either

1. FPC connector (it looks pretty good and its not damaged so I do not think it's the problem)

2. A chip? On the logic board that is defective and needs replacement.

I looked it up a little and I suspect that the U17 Chip could be defective.

U17 Chip

Can someone clear this up for me, could it be the U17 chip or another chip that controls the camera and if so where is it located and what is it called.

I am not a native English speaker so please excuse my mistakes.

Thanks in advance