Help the chip of my ipod gets really hot

This is my father old ipod classic. The battery wouldn't charge anymore but het loved his ipod. So I offered him to fix it. I put a new screen, battery and sd card storage in it but now this chip overheats. It does not turn on with the old battery and with the old screen and storage it still overheats.

Could it be a problem with the new battery or did I break the circuit board? How can i check this?