You're all so kind! I spent some time looking at a number of RK3188 tablets (including Teclast, Pipo, etc), and gave up. But, being one who always enjoys a challenge, I tried to see what I could do to rescue the tablet, or, failing that, to remove the internal SD card (data security and all). I am pleased to say that I have some good-ish news.

After a bit of effort (removing broken electrical stuff, gluing some things, poking here and there, etc), I have managed to salvage something. The tablet boots up, and all the functionality seems okay at the software level. But there is no volume button, or power button (well, they are sort of "there", but they don't work, because they are not now connected to anything). I can switch the tablet off by using an app. I can switch it on by just connecting the mains power. The big problem was how to wake it up from sleep. I then discovered (quite by accident) that removing the external SD card wakes the tablet (I guess doing that sends a hardware signal).

So, in effect, I have a tablet that I can use - but I am stuck with the current volume setting, and I have to do drastic stuff to wake it from sleep. I'm sure that there must be apps out there that let you set the volume through software. The struggle continues ...

Hmmm ... the two speaker icons at the bottom of the screen control the volume (duh!) - so I do have volume control after all.