This has to do with missing ringtones. I have a ZTE maven 2 model 851. My phone just upgraded itself to Android 7.1.1 All of a sudden (around the time of the upgrade) most of my sound appeared to go off, but the phone still made its startup sound on power up and a beep when I hit a key. But I had no ringtone when someone would call in, and when I tried to select a new one there was no playing of the ringtone. After a long time puzzling over this I finally went into SETTINGS - SOUND, and noticed DOLBY AUDIO sound enhancement was ON. I had not set this, and had no idea how it got set, so I set it OFF. After this my ringtones came back and everything appears normal, at least as normal for this phone. Hope this helps someone.
This is where the difficult rating comes in. Could use a picture from the other side of the port showing the small electrical pins. After all the work to get to this point, this is the easiest step to fail on and ruin the phone. The soldering guide does not cover this size, even under advanced. A proper soldering station heat gun seems the way to go.