TYT MD-UV390 firmware updates and unlocking

I recently purchased a TYT MD-UV390 dual-band DMR radio. In the process of updating firmware, uploading the CSV contacts file, and fiddling with codeplugs, I found that it eventually just stopped receiving anything! I couldn’t tell what had changed because I had made a lot of changes before I noticed.

Symptoms: I couldn’t hear anything on digital or analog channels. The receive light would go on, but nothing broke squelch. I listened with another radio but I couldn’t hear any transmissions I made with the UV390 either.

With experimentation, I found that updating the firmware to version 18.03 had “broken” it. This firmware version apparently defaults the radio to a “locked” state, so you cannot tune to normal ham frequencies. To unlock, hold down the buttons above and below the PTT button while powering on the radio. This restored functionality to the radio.