Burnt backlight diode on iphone 6


I have an iPhone 6 with no backlight issue, checked the continuity on the backlight path and all are okay, inspected the coil and diode, and noticed the diode was burnt, so I proceeded to replace it and as soon as I connect the board to power supply, the diode emitted some smoke and it was burnt again. I tried to replace again but it was still burnt again. Polarity is correct and all path is ok, anyone can advise why the diode can burn as soon as I connect to power supply or battery? I could not trace where the problem is…

Thanks for any input and advice!