Any way to fix overheating logic board of iPhone 12 Pro?

Hi,

i bought a defect iPhone 12 Pro to harvest the Screen. The iPhone seems to be brand new.

The defect is, that it overheats (see marked spots in picture) while in use and gets fairly hot while off (including not normal battery drain while off), also the bottom loudspeaker is not working. Everything else works.

Someone before me seems to have swapped the battery for an aftermarket one (and soldered the old battery-chips to the new one). Everything else seems to be OEM and untouched. No water damage.

Here is what i already tried to narrow down the problem:

• Swapped bottom loudspeaker - still no sound
• Disconnected both connectors to the charging port assembly (including bottom loudspeaker) - no change still overheating
• Swapped battery - no change still overheating
• Display works fine in second iPhone (non pro)

This is an issue with the logic board (and probably the audio driver chip), right? Or does anyone has other ideas?

If I buy a new logic board, I still need matching FaceID assembly and Lidar to get everything working even with iOS 18 repair assistant, right?