Annoying ambiguous Android audio anomaly.

Factual Questions
1

I keep around a small stack of old Android phones that I use for various things in Airplane mode or have for spares if needed. A couple of days ago a cousin ran across an LG K7 4G K330 that she had replaced and left unused for at least a year (it was fully functional at the time, she just upgraded to a Galaxy S8.) She passed it along to me. I was pleased to have it because it has a pristine screen and would make a nice EPUB reader.

The battery was fully dead, but I charged it for a while and it booted, but then hung just as the desktop came up. Locked so hard that I had to remove the (luckily, removable) battery to turn it off. This happened with a couple of more tries, but googling told me a key combination for booting into a factory reset. So I did that, set it up and started sideloading apps, but soon it locked again. Repeat battery removal, factory reset. A couple of times doing this and I finally noticed that the phone wasn’t making any sounds at all. I tried the built-in sound recorder and it would seem to be recording, but trying to play it back would generate an error message. I installed my favorite media player (MX Player Pro) and copied over some video files, and when I tried to play them audio option boxes were unchecked and I couldn’t check them again.

When I plug in a pair of headphones, not only is there no audio but the headphone icon doesn’t even pop up. I couldn’t get it to connect to my Bluetooth speaker. And when I try turning off the audio in Settings (with the plan to turn it back on again to see if that would help) I get the hard freeze that needs a battery removal and factory reset. As far as I know, the earlier freezes could have been audio-related, too–the “turn off audio and lock down” one is constantly reproduceable.

So–any clues what is going on here? Hardware failure? (There is no color change on the water damage detectors.) Corrupted driver that remains corrupted after a factory reset? I don’t Need Answer Fast and could just throw the thing away, but I’m perplexed about what is going on here.

2

Driver issue, or the DAC is fried, or the phono jack is (partially) broken from the motherboard and short-circuiting?

Some LG phones have had issues with overheating, which leads to warping of the motherboard and permanent/intermittent malfunction of ICs. (My current LG overheats when the brightness is above ~50% and the screen glitches. Not buying LG again.)

If you can read ebooks without crashing the OS, do that. Otherwise, ditch it. It’s probably fiscally illogical to spend money on diagnosis/repair.

3

Yeah, that’s what I was planning on doing–definitely not putting any money into it.
I noticed something else today–the GPS doesn’t work. Holding this one and my good phone side-by-side, my good phone sees 14 satellites, the LG one sees zero.