S7 (G930F) bootloops and overheats

We've got an S7 in at the moment, the volume up button and surrounding chassis was damaged. When it came in it was stuck on a blank screen with the blue LED pulsating and getting extremely hot. Tried a soft reset and it just boot-looped over and over until the battery died.

I have reworked the chassis and button and got it clicking again.

Once this work was complete, it then went through the boot process, got to the home screen and rebooted itself. and started boot-looping again.

Sometimes it will go to the Samsung logo and reboot, other times it will go to the 'Android is installing apps' or 'Installing system update' with a green screen or whatever it says.

I have re-flashed Android 7 (latest firmware) which was on the phone already but no luck. I also tried flashing Android 6 but the problem still persists.

I have tried a new battery with no luck.

I have looked around online and cannot find much apart from 'take it back to Samsung'.

The customer has since purchased a new phone so there is no rush to repair this.

Any help would be great.

Thanks.