I now own a computer I've been wanting since the '80s for no reason other than it's as utterly cheap in price and quality as a fully functional home computer could get: A Timex Sinclair 1000. The picture quality is delightfully crappy. Unfortunately, half the keyboard doesn't work, which probably means its super-cheap ribbon cable kinked & broke.
Oh, wow, fantastic ideas if I can't repair the membrane keyboard, made all the better by the fact that I work next to an indy Radio Shack dealer.
A DIY ZX81 Keyboard Period Document: http://www.zx81keyboardadventure.com/2018/06/a-diy-zx81-keyboard-period-document.html
Timex Sinclair 1000 (USA's ZX-81) repair (+)
The replacement ZX81 keyboard arrived, and the ribbons look and feel much more substantial. The only cosmetic differences are a slightly different font, shift-0 is rubout instead of delete, and enter is "new line" instead. Time to clean off the gunk from the top of the case so I can put the new keyboard in.
Timex Sinclair 1000 (USA's ZX-81) repair [++]
It works! I should probably remove the RF modulator cover & see if that can be cleaned up, but it works.
The test keypresses were: P {Shift-P} 1 2 3 4 5 6 7 8 9 0 Q W E R T Y U I O P A S D F G H J K L {Space} {period} M N B V C X Z {Enter (now New Line)}
I also had a kaleidoscope program in a .wav file ready for testing. Android won't let you keep the headphone jack volume at "Marty McFly," but the Sinclair can't hear anything softer.
I can see why the RAM pack is bolted on now. The case top standoffs look okayish, but the case bottom standoffs that are supposed to meet the motherboard & let the screws hold it on are completely missing, filed & sanded down to nothing. The motherboard is now so misaligned that the pack is actually suspended in the air, held on only by the edge connector & the weird support bracket. Any movement of the bracket makes an edge connector pin break contact.
The little I've been able to read suggests this is just the way it is, due to the ZX81's lack of porches in the video signal. So I either live with it or do a composite mod.