[Nexus 7 Android Development] Andy2No:
The equaliser thing may have just been because I had another app installed that took over the equaliser function. I forget what it was called. Something to do with headphones and the word equalizer...

Interesting. If I ever get it to turn on again, I'll try doing that.

I decided to try changing Gapps to Pico Gapps. I read that you could just format the system partition, install the ROM you were using again, then the new Gapps. That appeared to work, but I couldn't get Google Play to work any more - I kept getting error RH-01.

So, I repeated the process (all using TWRP 3.0.something), putting back the recommended mini dynamic Gapps. Again, it seemed to work, but now Google Play was just blank, with a whirring busy icon. I tried setting permissions, clearing it's cache and data, wiping the dalvik cache and mumbling incantations while wearing long floppy sleeves a big pointy hat. Still no good.

So, I tried to restore a backup, with TWRP. It failed, with an error code 255. I decided to try upgrading TWRP to the latest one (with fastboot), and also deleted some files because apparently error 255 can mean there's not enough free space to work with.

I then tried the restore again - same error. I then tried rebooting and it now won't turn on at all. I don't just mean it won't boot, I mean it's completely dead.

I've just taken the back off, and unplugged the battery for a while - a scary procedure that looks likely to damage the cable because all you can really do is pull on the wires. Trying to prise the plug out of the socket is a non starter.

Still no luck though. I now own a shiny black paperweight. I should never have started trying to make it work better, since it did actually do what I needed it for, before that (when it was in the mood).

Incidentally, I bought a micro USB extension cable. It worked for charging and file transfers (when it was in the mood) but as far as I can tell, not for OTG USB audio. Given how awkward it can be to get that to work, it took me several attempts to be fairly sure of that conclusion - that was before I turned it into a paper weight, of course.

---------- Post added at 05:43 AM ---------- Previous post was at 05:00 AM ----------

Okay. Some progress.

It turned out the one thing it would do is charge - at a lower rate than I'm used lately (0.38A on my USB power meter vs the usual 0.53A).

It was more or less fully charged before I tried the restore, then updating TWRP and so on, so I don't really believe the battery went flat while I was doing it, especially as it was cabled up to the PC, most of the time. However, it's quite possible the tablet did believe the battery was flat. I understand they can get a false idea of how much charge is in the battery.

After the battery unplugging, then some charging while watching more Youtube videos about unplugging the battery, I was able to get it to turn on again - still showing an empty battery. I've left it on standby, still charging up.

It does appear that the restore worked, despite the error message and failure to reboot, or even turn on again afterwards; the screen is back to how it looked before I disabled, then uninstalled, the Google app. I still don't want that, but I guess I'll leave it there, for now.

I'll provoke it some more once it shows a full battery, assuming that happens, and see if Google Play is working again.