A coworker brought me his G2 that I have taken apart to fix many times before because it was having problems charging and turning on (black screen; rhythmic buzz from the vibration motor). I worked around that to get it booted temporarily but then the SIM connection seemed to suddenly fail. I replaced the motherboard entirely because some charge/power issues persisted and everything works perfectly EXCEPT that the replacement also doesn't see the SIM. Both are running stock LG Verizon Lollipop (assumed installed by OTA). No one was playing around with alternate ROMs or anything. None of the fixes in this thread help. The SIM slot is on the board so I hesitate to assume that the charge, mic, headphone flex PCB has something to do with it, but it is the only major common component (even replaced the screen again along with the battery, speaker, etc while leaving out useless components). Any suggestions?
Long version:
After a previous screen replacement it would only buzz when attempting to turn on or buzz repeatedly when attempting to charge until I loosened the black screw near the battery connector. I definitely narrowed it down to that particular screw, though I still couldn't say why (the previous tech who replaced the screen may have shorted the battery terminal near there). When he brought it back to me it was doing the same thing again even with the screw completely removed. Within minutes I had it booting just by poking around. Not sure what I did but I had to take it apart and poke around again to get it to come on after making the mistake of turning it off (went right back to buzzing). I'm pretty sure that the SIM card worked because he received a couple text messages when I first got it turned on (phone hadn't been booted in a day). After getting it to turn on I had to leave it on while reassembling, so I put the SIM tray back in when I was done. The owner was watching and asked why the status bar showed an "X" on the signal strength, so I told him that it was because you had to reboot after reinserting a SIM on most Android devices (as opposed to dual-SIM and iPhone devices). Though I couldn't turn off without causing the power problem, I could safely restart. Unfortunately, restarting only gave me the "Insert SIM" message at boot and nothing I could do would get it to see the inserted SIM. I tried many SIM cards but none worked. I replaced the motherboard expecting it to be a solution to both problems but only the power problems went away. The SIM card issue remained even though the SIM slot is built into the part I replaced and the part I purchased is supposed to be guaranteed, tested, clean IMEI, etc. I'm at a loss. I've taken out every unrelated component and replaced the screen again and replaced the battery so about the only thing that is common is the flex PCB with the mic, headphone jack, display connectors, etc running through it. Not sure how that could be a factor, but I'm replacing it too. In the mean time, does anyone have any suggestions for what could be wrong?