The thermal camera answered a focused question
The supply first established that the board was drawing into a short. Thermal imaging then showed which component was dissipating that energy as heat, narrowing the investigation without blind component removal.
The finding was U4000
The abnormal heat centred on 343S00946-B0 at board designator U4000. During the recorded test it reached roughly 93°C while the surrounding area remained much cooler. That contrast, combined with the electrical behaviour, supported replacement.
The short was checked again after replacement
After fitting the replacement controller, the board was checked and the short was no longer present. The reel later records input power returning. Those observations describe this repair rather than a universal iPhone 15 fault pattern.
Why a dead phone still needs diagnosis
A black screen and zero input can arise from several power, connection and board faults. Thermal localization is useful only after controlled testing establishes what should be energized and under what limit.
