"Different" ZX81's

[Lardo Boffin]

Check out those capacitors!

[Lardo Boffin]

And another one with cool capacitors. Sadly this one needed both a new ULA and Z80 to work again. But thanks to Andy it is alive and I can release it back into the wild again.

[Lardo Boffin]

This seems to be turning into the Lardo Boffin thread. It makes me wonder if I need to stand up at a meeting and say ‘My name is Lardo and I cannot stop buying zeddies’....

Regardless:-

Nice and early ULA. 8112. I think they started in 8109? So pretty early! Not tried it via RF yet but works great with my Chroma and ‘Spand.

Also when I type PRINT SQR 0.25 I get this :

So its an early bugged ROM. Nice.

I will be testing it and putting it up for adoption on here if anyone is interested. I don’t like refurbing the interesting ones like this. But it will need a new membrane (unless you use a plug in keyboard like I did - my trusty Memotech) as the current one is shot.

[Lardo Boffin]

Interesting resistor packs. This zeddy has clearly been repaired at some point (ULA is 3 years younger than the PCB and has a green turned pin socket) but I doubt they would have replaced these?

[1024MAK]

Don’t forget Sinclair/ Timex used whatever parts they could get the best deal on at the time.

Also keep in mind that in the early 1980s, the computer industry (for mass production computers) was still young. So there was probably also the issue of suppliers having to step up production to keep up with the number of units being sold. So it’s very likely that sometimes Sinclair/ Timex had to buy what was available. And it’s always a good idea to have the option of buying from at least three different suppliers.

Being an electronic geek, I actually have some very similar black resister networks in my parts drawers. The green/white type I have seen before. I can’t remember on what board, but it may have been on a Zeddy... (when I actually find myself with some spare time, and I can stay awake long enough, I have a look at some of my Zeddies...).

There is more than one way to make a resistor network. Hence the reason they look so different.

In digital electronics, it’s rare that resistors get changed. 5V is low for components that have a voltage rating of 125V (or greater). And often a slight drift in resistance value does not affect circuit operation.

I’m surprised you have not noticed these variations before

Mark

[Lardo Boffin]

Just had a quick look at the photos I have posted and I have only ever really seen the ‘common’ black or blue resistor packs.

Clearly this indicates I have never seen enough Zeddies and need to see more.

[Moggy]

Just to concur with Mark I have had that pack on boards past and may still have one on a scrap board.

[Moggy]

First one I dug of my scrap pile....

[1024MAK]

Clearly this indicates I have never seen enough Zeddies and need to see more.

Mark

[Erm]

I noticed something so anorak today that it is (almost) embarrassing!

There are different polystyrene packaging parts, with slight mould differences to both halves.