On the membrane keyboard, it's definitely something you don't want to do a lot of typing on, with barely any feedback at all. I keep expecting it to beep like a microwave's keypad. But to be honest, the keys that work feel better than any smartphone's on-screen keyboard I've ever touched.

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

This both complicates things and explains why so few keys worked. Both ribbons were almost completely separated at the connector, & the bits still clinging on snapped right off while carefully lifting the board out. Bits of keyboard are still in both connectors.

The keyboard ribbon has breaks going too close to the keyboard itself, so it's looking like I'll have to hit up sellmyretro after all.

But I now have a hardware reference for a DIY keyboard, not just a PDF scan.

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.

I'm not sure how to get the last layer of adhesive film off. I know it's there & not just case tackiness because a corner is actually clean & smooth. But a Magic Eraser doesn't seem to be doing anything.

Correction: Now it's making progress, but it needs lots of elbow grease.

Back to cleaning the Timex Sinclair 1000 case so I can install the new keyboard: I gave up on Magic Eraser. I'm making much more progress with some Fast Orange and a cheap toothbrush.

You can see my progress in the left corner. I got about 3x as much off in a few minutes with pumice soap than I did in several hours with Magic Eraser.

A nearly clean surface & a toothbrush rendered filthy from scrubbing it. That's looking nice. :3 The surface where I'm scrubbing hard is getting scuffed up, but that's actually a good thing; the new keyboard's adhesive should grab better.

That looks about as good as I can get it.

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 should look at the RF modulator in the nicer-looking one next.

But for the desperately modded one... Woohoo!

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.

Tilted Goldeneye carts aside, computers generally don't like it when parts of the memory map suddenly go missing.

Well, that's a new one... I left it alone for a while, then when I went back, it was doing this weird coloring thing. I started a game then took a photo:

I left the ZX81 alone in the kaleidoscope program, and after the same long delay, it started the weird colors again. I turned the TV off and back on, and not only were the colors still there, the TV took most of a minute rolling, fading to & from static, alternately showing something & "no signal," to sync with the ZX81's signal again.

Now I've got to either dive into uncharted territory (the RF modulator) or look at a composite mod. Help & pointers appreciated.

@arielmt US version of the ZX81?

NGL those early membrane keyboards give me nightmares, i'm glad my first sinclair machine had actual keys on it (+2 128k speccy that i still own)

you can still buy new keyboard membranes/connectors for em for relatively cheap, iirc

@arielmt Oh wow, the membrame keyboard...
I guess it was only the successor that had "real" keys, and even those were horrible from what I hear.

@arielmt Wow, I guess age really embrittled it, huh?

@pettancow Kinda looks that way. What I find most surprising is that the entire rest of the ribbon is in excellent condition for its age, and that there isn't any heat-related aging anywhere along its length, let alone where it rested directly on top of the chips.

@arielmt I guess the tensile stress from the kinking exacerbated it. o:

@porsupah Oh, it's definitely the keyboard ribbon in both cases. They all but completely disintegrated in both ribbons at both bends.

I should probably give the boards a thorough once-over all the same. The video quality from one-meter RF cables is worse than a low-power TV station over 100 miles away.

@arielmt Ouch! I suppose that was inevitable. ^_^; How feasible is replacing that?

Mm, I can imagine the modulator having degraded over time, unless you're maybe looking at hacking a composite output into it.

@porsupah There's a UK auction site called SellMyRetro, and one of the sellers there makes and sells replacement keyboards. They're UK-specific, but the only thing Timex did different in the US version was some wording on top.

@porsupah Replacing the RF modulator? Yeah, some folks refined the composite mod to be pretty reliable, and some are selling assembled drop-ins that can fit into the RF box. (I'd like to keep the RF if I can, so yep, troubleshooting that is next.)