This is a backlight problem on the logic board. The 6s plus has two backlight driver IC’s One of them has failed causing the problem you are having. You will need to replace the faulty IC by a reputable repairer.
You will need to re-ball the baseband CPU but being the Qualcomm model the baseband will probably be shorted internally. If it is you could try burning the short out but it doesn’t have a good success rate. If the keypad brings up the IMEI you might just get away with re-balling the BBCPU.
It depends on where you are selling it. I never use wireless charging and no one I associate with does but you will have to weigh up say $150 to get the charging working to what you will get with it not working.
You need to determine if it is a parts problem of a component on the logic board. · Can Siri hear you? · Will voice memo let you record? If voice memos will not let you record you most likely have the signature audio IC fault which occurs on the 7 series. This repair requires microsoldering. If voice memos let you record and Siri can hear you I would start by replacing the dock connector. and front speaker flex assembly.
There is no way of knowing what component has been damaged from the dent. The only thing you could try would be to rule out parts. Try a replacement battery and screen and make sure all the connectors are sitting firmly, other than that you would need a multimeter and DCPS to find the faulty component.
· Did you replace the battery after you purchased it? · How many amps is it drawing when charging? · What does 3uTools say about the battery and its health? You will need to rule out parts. Try another battery and dock connector. If it is indeed fake charging I would replace Tristar.
If the screen responds to touch it is more likely a backlight problem. Shine a torch on the screen and see if you can make out an image. If you can there is most likely a faulty component on the logic board backlight circuit which would require microsoldering to repair. This shouldn’t have occurred if you disconnected the battery before doing the screen replacement so I wouldn’t rule out a faulty screen that has ended up damaging one of the backlight components on the logic board.