iPhone 6: stuck searching but WiFi, BT, IMEI and modem work

Hi everyone,

I recently picked up an iPhone 6 for £55 - bargin! The problems were described by the seller as: terrible cosmetic condition, cracked and unresponsive LCD, and stuck "searching".

I've replaced the LCD and it works great, and a new back cover is on the way. However, there is one thing that I haven't figured out. The phone is stuck "searching" despite all resets, etc.

Reading on the forum, it would appear this issue is common, and almost always ends up at a semi-fatal 'dead RF chip' which needs reballing. However, I appear to have slightly different symptoms...

1) WiFi and BT work fine with good stength

2) The 'About' page is fully populated with the IMEI number and modem firmware info

3) When restoring the phone, I didn't get any errors apart from -50, which appears to be down to activation (assuming that lack of celullar connectivity caused this).

4) However, when entering *#06# into the dialer, nothing happens

From my layman's perspective, an IMEI and modem number in 'About' suggests that there isn't a fault with any chips. I've checked the cellular antenna connection at the bottom of the phone, and have ordered a new docking port to try and eliminate the possibility of bad connection to the (beaten up) case.

I confess to trying the quack method of dropping the phone onto a desk, unsuprisingly this didn't do anything. When I recieve the parts I've mentioned, I'll take out the logic board and inspect for damage. It seems the previous owner had the screen replaced at some point.

Can anybody shed any light on my problem? Thank you!

EDIT:

Forgot to mention, the date and time is set correctly. I know that the incorrect time will cause this issue.