exxos's Atari, Amiga & retro forum

Well, the vLA81 arrived, but didn't fix the ZX81.

Something else was wrong, so I did some probing with the scope and found no address or data line activity at any of the places that were supposed to have them.

Figuring that the RAM and ROM might be a bit harder to get hold of, I managed to get a Z80A cheaply from eBay, and what do you know, the original CPU was also dead!

So with the new CPU and ULA installed, plus the composite video adapter, we now get this:



The picture is great, and the new keyboard works a treat, very happy to have brought this back from the dead 😁.

Next for this little wonder, and the 65XE it's sat on gives an idea of scale, is to get the RAM pack, made by Memotech, back to working order.

Got a bit of a smile on my face 😁

Nice :thumbup:. I haven't had my ZX81 out from the loft in a long time. Looking at these pictures makes we want to start back on the ZX81 but I have way too many projects on the go.

Glad to see its working again @rubber_jonnie

Icky wrote: 13 Dec 2020 18:29 Nice :thumbup:. I haven't had my ZX81 out from the loft in a long time. Looking at these pictures makes we want to start back on the ZX81 but I have way too many projects on the go.

Glad to see its working again @rubber_jonnie

Cool thanks @Icky, it has been gathering dust for so long, I just had to get it done!!

Trouble is with my projects, we are trying to move house and I've been working throughout the lockdowns, not to mention the elderly parents in need of help, so hence I have not been as active, so as soon as I can I need to finally fix my other Mega, get my other H4 built and crack on with my other projects.

Good thing is, if the move goes to plan, I will be able to get a proper workshop set up, so it'll make getting on with stuff much easier.

I might even be able to have more than one project on my workbench at a time!

:girldance: :bravo: :yay: :cheer: :dualthumbup:

@stephen_usher glad to see you're part of the ZX81 club too😁

Yeah, that's my original computer. A Christmas present in 1981. I had to wait for my birthday to get the 16K RAM Pack.

I've fitted the LA81 in the machine as it had the original ULA which didn't produce the back porch and hence wouldn't really work on any telly which wasn't an old B&W CRT.

P.S. My current project is getting an Amstrad CPC 464 fully operational again. I "accidentally" won it in an eBay auction as I put in a bid and thought I'd be massively out bid but wasn't. Turns out the parts I need (a couple of keys and the cassette mechanism) are going to cost me more than the machine did (~£35 inc. postage vs. ~£50 for the bits).

stephen_usher wrote: 13 Dec 2020 21:54 Yeah, that's my original computer. A Christmas present in 1981. I had to wait for my birthday to get the 16K RAM Pack.

I've fitted the LA81 in the machine as it had the original ULA which didn't produce the back porch and hence wouldn't really work on any telly which wasn't an old B&W CRT.

P.S. My current project is getting an Amstrad CPC 464 fully operational again. I "accidentally" won it in an eBay auction as I put in a bid and thought I'd be massively out bid but wasn't. Turns out the parts I need (a couple of keys and the cassette mechanism) are going to cost me more than the machine did (~£35 inc. postage vs. ~£50 for the bits).

Yeah, I suspect my old ULA may still work, but also being an issue one suffers the back porch problem too. I do have a TV that it would probably work with, but the modulator has been gutted and I fitted a ZXVID instead, so get a real nice composite signal as you can see.

I think the computer cost me £20 from eBay (My original and I parted ways a long time ago), and with the new keyboard membrane, vLA81, new Z80A and ZXVID, I reckon it cost me close to what an original assembled one cost back in the day. Nostalgia is a powerful thing.

I do still have my original Atari 65XE though, and it's original cassette deck.

RAM pack is the next thing to fix, then maybe see about getting a ZXPAND interface for it. Also have a Spectrum + that's in the queue for the operating table.

Good luck getting the CPC back up and running again :)

Thankfully the main PCB of the CPC is happy. It just needed a lot of cleaning and the edge connectors were so oxidised that I had to use very fine grit wet&dry sandpaper to remove the corrosion!

It's an early model machine and so it has a steel plate for the keyboard, which has rust spots EVERYWHERE! Thankfully all the keys work. only the -/= key cap mounting cross has broken and will need replacing. I can still operate the key though by pushing it down the hole with the end of a finger nale, so the mechanism still works.

I must admit, of all the 8 bit machines I've played with the CPC does seem to be the best (I know, I'm a heretic :-)). I still don't know how the engineers got the ground breaking design through AMS as no doubt he'd have wanted the cheapest piece of *beep* out of the door in the same way he did for his HiFis.

Sounds like a plan, I'll bet you have it all fixed in no time!

I watch quite a lot of Noels Retro Lab, he's done a lot on the CPC, oddly though I never really wanted one, though you never know once I've moved and have more space! My favourite 8 bit machines are the Ataris I must admit.

With regards to corrosion, I use a fibre glass pencil, they are cheaply available on ebay, and are very controllable for spot cleaning of corrosion, plus very much finer than wet and dry.

Keep us posted on progress, and as for AMS, maybe he had an off day 😁

So, I'm thinking that the problem with the ZX81 16K (That size seems so hilarious now) RAM pack is actually power.

The old ZX80 PSU that came with is is a bit weedy, so I think I need to see if running it off my bench PSU with more than .7A will let it spring into life, because it just seems like it just isn't powering up with the pack plugged in.

More to follow!