[Galaxy S III Q&A, Help & Troubleshooting] Pindwe:
My girlfriend has had a Samsung S3 (I9300) for a couple of months and has had no issues with it however she dropped it and broke the LCD . I ordered a replacement screen (Front glass, LCD, and digitizer) from eBay and fitted this without any problems. I tested all functions on the phone and it seemed to be working okay. The same evening my girlfriend went and run the update and went from 4.0.4 (I think) to 4.1.2 since then she has complained about signal issues which I have now witnessed myself. I wished she had waited a bit longer to make sure the phone was working fine before doing any updates as now I am not sure if this is a software related problem or hardware. There is no way to revert back to the older version to confirm software. I know one option on the software side would be to root it and install a customer rom but I have never done this before and even though reading through the forums the process seems to be easy I am a bit reluctant to do this just now.

The signal indicator sometimes shows a circle with a line through it, sometimes it shows a grey triangle with no bars in it and other times it will show a bar or two and even a full signal. I have noticed even without a sim in it that it can show a couple of bars of signal. I have not got this confused with the Wi-Fi signal. When trying to send text messages or make a phone call the following errors come up “Not registered on network” and “No signal found for mobile network”

Below is what I have done/checked so far

I have restored the phone to factory settings but as explained before this will only restore to 4.1.2. This time the only apps on the phone are stock apps, no additional apps have been installed just encase a third party software may have caused issues.

Her sim will work in any other phone. I have an S2 and have ported my number over from a normal sim to a brand new micro sim to try in her phone. Both of these phones are on O2.

I have made sure the IMEI number is correct and matches what the phone came shipped with.

I have double checked the APN details and these match what my S2 has. Although I am pretty sure this is only for internet and MMS and would not affect SMS and phone calls.

After check over the settings and restoring to factory settings I have fitted a replacement antenna which I also got from eBay. I doubt I have damaged the mainboard as all other functions on the phone work fine. (Touchscreen, Cameras, Sound, Wi-Fi)

For some reason I can get the phone to work at my house on both GSM (2G) and WXCDA (3G) although it seems to be more stable when it is on GSM. As soon as I leave my house and go into town (approx. 2 mile away) or over to my girlfriends (approx. 20 miles away) it will stop working. I have gone onto the O2 website and entered both of our post codes on the O2 network coverage checker and this reports that there are no services down in our area and that we should have a good signal.

I have come on this forum for some advice and hopefully someone can recommend what I could do next. I have had a little browse on the forum already but is there something I have missed? Should I root the phone and install a customer rom? If it was caused by the official update is there an a hotfix of some sort coming soon? Or is this a genuine fault with the phone? If it is a fault with the phone and it has not be caused by me I could try sending it back to O2 (where the phone was purchased from) or Samsung seeing as I can’t see any warranty seals so think I would get away with this.

Thanks in advance for any responses I get to this and I am sorry if I have rambled on and provided info that is not essential.