Owner told me, at once the display stopped working. Right in that period he was in a wet region. Ok, probably water in the camera.
I opened the back cover – nothing. No sign of water, nowhere. Fortunately I had on another 500d on the table 🙂
DC-board – good.
Back LCD – good.
Top cover – good.
Flex cables – all good.
Main board – bad!
As a main board is very expensive, the customer decided not to repair the camera, he wanted to use it without the LCD. I started to assemble it. And at once – I have picture on the LCD for 1 second.
Ouuppps. Disassembled again, and – as I supposed, it could be some condensed water under the BGA video chip, I sprayed with some Methanol (CH3-OH – dangerous but very good for degreasing and taking out water). I blowed with some air – and LCD WORKING continously!!! I diceded to continue the cleaning, but at the end the picture dissapeared again.
I think, there is a simple problem with the BGA soldering (the man who invented the BGA technology was an idiot – all notebooks and everything, which produces uneven heat dies because this shit). The methanol solved the problem probably only because the cooling effect, which bended back the chip to the surface – I will have to buy a freezing spray.
The same problem appears by other cameras too, but with other chips – 40d for example th Digic….
DIGITAL CANON repair blog 
Maybe some hot air could solve the problem – Sometimes BGA’s can be repaired by re-heating, but is not too reliable.
I think the same about BGA’s as you, too.
as I repair cameras for other people (for money), I cannot afford a half-solution. Using the heater can work – but will never work 100%, as the soldering material is already oxidized. Sio, I can use this for a temporary check, just to demonstrate, what is the failure – but for a BGA chip with 200-300 pins will not be adviceble.
Nice Sharing 🙂