This is a fairly common problem on the iPhone 6 and 6 Plus. The phone will not be able to pick up a signal or it will become very intermittent with it saying “Searching” then bringing up “No Service”. Also if you type in *#06# it will not display the phones IMEI number.
This is basically an issue with the Baseband chip. The phone would have probably suffered a bad drop or because the housing isn’t that strong the constant flexing would have caused it. This causes issues with the solder balls cracking and damaging the actual solder pads the chip sits on. The two solder pads that are most commonly damaged are U1 and V1. Therefore to fix the issue the chip needs reballing along with damage to the solder pads repairing.
When buying screens to use in repairs for iPhone’s and other Apple devices they can vary a lot in quality. Despite what people might say unless they are taking their parts from used Apple devices they will never be 100% original. This is because Apple don’t make or supply parts to third party repairers.
You can however get hold of OEM (Original Equipment Manufacturer) parts, whereby the part isn’t coming directly from Apple but is produced by the same manufacturer/factory Apple use. As an example the complete iPhone screen consists of different components that are all made by different manufacturers. The LCD part is produced and supplied by LG and Sharp as well as a few other companies. Then the glass touchscreen, frame, flex cables will all come from somewhere else.
You can get hold of iPhone screens where every component will come from an OEM manufacturer/factory and these are the best quality. At Gadget Repair Nottingham these are the screens we use in our repairs.
You can buy other screens that will have some OEM parts and other Non-OEM. For example the LCD might be OEM but the glass will be from a Non-OEM source. Obviously the price is reflected by the quality down to the cheaper ones you generally find on eBay or offered by some other repairers that can consist of complete Non-OEM parts. These are the ones that tend to have issues with things like clarity of the LCD and colour/quality of the glass.
It is therefore important to understand that the quality of the repair is heavily influenced by what parts are being used.