Chosen Solution
I just repaired an iPhone that had the no service issue. Now it is working on Verizon and will only get 1x (before it was no service for everything). I can’t get it to connect to verizon LTE or T-Mobile at all. I know the board is good because it works with 1x on Verizon. What antenna would affect LTE performance?
Don’t be too quick to assume the board is working. The iPhone 6 series has a well known design defect that causes Searching/No Service issues. After you have eliminated antennae or network locks as the possible culprit, searching issues on the iPhone 6 are usually related to the baseband IC. The baseband IC is very sensitive, just like the Touch IC’s on the 6 Plus; it also suffers from poor quality traces and pads. Go to your phone’s dialing keypad and dial *#06#. You should see the IMEI displayed. If the IMEI is not displayed, the Baseband IC has to be reballed and two small copper traces (U1/V1) have to be rebuilt and solidified. This is commonly referred to as the “long jumper” solution. You can check out this answer (Service is “Searching” indefinitely) (by @teetopp) as it summarizes the issue really well.
