Hardware?

so I've been fixing iPhones for a few years now and never had any issues, i was given a white 5 to repair after the owner had tried to repair the screen by fitting a new one and they had damaged the lcd resulting in green lines, i popped a new lcd in and gave it back, they then said it would charge so i took took to back had an inspection and thought that the dock connector doesn't look healthy.

i replaced the lower assembly and still no fix? the phone seems to be functioning however when i play something through the phone such as a ringtone the phone just completely shuts off instantly? and the it needs to be turned on again? the phone doesn't respond to power no matter ** many genuine cables i have tried, from plugs and a macbook, i have tru=ied numerous hard resets etc...

i believe that whatever has been caused by the owner but i want to get to the bottom of it! any ideas or what to do now??

My idea is to chuck it and call it a day. There is no telling how much damage was done the first time he broke it and tried to repair it himself. This thing is a complete lost cause. Some things just can't be fixed.