"Different" ZX81's

[Fwapp]

I'm one of those weirdo's that like to collect the different variations of ZX81 - the ones that are a bit different from the "normal" types that you see. I've taken a few pictures for a FB group, so I thought I'd post them here.

First one is a US ZX81 - Issue 1 layout, but unlike the UK version it has straight PCB traces and the soldermask is red. It's a bit weird to see an Issue 1 that isn't all nice and curvy, although it looks nice in red

ZX81USA.JPG (158.64 KiB) Viewed 10954 times

Second one is Issue 1 with an eprom, instead of ROM. I gather this was due to Sinclair running out of ROMs and needing these in a hurry? I've seen this on Issue 3 PCBs but this is the first time I've seen it on an Issue 1.

ZX81I1Eprom.JPG (175.15 KiB) Viewed 10954 times

Anyone else got any oddities?

[Lardo Boffin]

Nothing weird about collecting the 'edge cases'. Unfortunately I don't know what's normal to know what's weird if you know what I mean?

If you post pictures of standard boards of each issue I can compare mine and and any more I see.

Lardo

[Fwapp]

I guess that'd be a good idea

Issue 1 PCB - normally has green solder mask, nice curvy tracks.

ZX81I1.JPG (127 KiB) Viewed 10925 times

Issue 3 - normally has red solder mask, straight pcb tracks.

ZX81I3.JPG (142.72 KiB) Viewed 10925 times

If you happen upon an Issue 2, it's worth nothing, just send it to me!

Sometimes the memory is 2 chips, sometimes 1, it seemed to depend on what Sinclair could get cheap.

Other flavours of ZX81 I've got are Issue 1's with 2C158E ULA, same with a kludge on the CPU to fix a bug in the ROM and an Issue 1 with a creamy coloured PCB. I have a Issue 3 with a ROM and an Issue 3 with green solder mask on the way.

By the way Lardo, I've just clicked that you are the kind gent who helped me out with a sideways RAM board over on *. nice to meet you again

[Moggy]

I would say that your EPROM mounted board is the nearest thing to an "issue 2" you'll get as it utilises an issue one board but the later issue 3 fitted ULA and post 81 CPU.

The USA issue 1 should be treated as a unique Timex board in its own right rather than a "nicer" UK issue 1 as it has components foreign to the UK board IE 2K ram, inductors, different modulator, channel switch, less resistors and some earthing(grounding) bits and bobs plus a different track layout.

The green masked issue three is the earlier of the two issue three boards.

[Fwapp]

Yes, that eprom Issue 1 is quite a late one, maybe Sinclair found a box of Issue 1 PCB's (or repair returns) and decided to use them? They did similar things on the Spectrum.

Sorting through some ZX81's I've found a Philippines made 2C184e with an 8221 datecode and a UK made 2c210e with an 8222 datecode - I wonder if the 2c210e started coming on stream before the change to the Issue 3 PCB.

Do we know why Sinclair moved to the Issue 3 pcb? It seems to accommodate the US case/shielding requirements easily, but I;m guessing it was also perhaps due to ease of production (automated lines, perhaps?)

[Moggy]

I would agree with your estimate re the 2C210E dated 82 being likely part of an in between state of play although the only issue ones I've come across bearing said ULA have been refurbs.

Your board though has the ULA soldered not socketed so unlikely to be a refurb therefore factory issued. the state of the solder work could answer that one.


As to why Sinclair migrated to CAD designed boards I would have thought the answer lies in the fact that Sinclair wasn't the manufacturer, Timex was, so board design and production would have been left in their hands and given that Uncle Clive tended to let others worry about the manufacturing side of things he probably just went along with what ever Timex churned out.

[Lardo Boffin]

By the way Lardo, I've just clicked that you are the kind gent who helped me out with a sideways RAM board over on *. nice to meet you again

Small world!

Did you manage to get that board soldered in and working ok? I meant to ask but life got in the way!

[Fwapp]

I did - with the same issue in Ghouls

[Moggy]

Just thinking about automated lines I have to say that any photographs I've come across re the Timex production line seems to show groups of women hand assembling/soldering everything so whilst the boards were machine produced I would guess the old assembly methods prevailed. Would Timex have invested in a fully automated assembly line given the set up cost for such a new product given that they were watch manufacturers primarily.


Just a muse on my part.

[Fwapp]

I agree - I can't see them moving to an automated line, just supposition on my part. I do wonder why they moved to the issue 3 and the whole associated redesign cost, and also the question of what happened to issue 2.

I was under the impression that Sinclair did the PCB layouts as well (Rick Dickinson saying he helped for the ZX80 in an interview I read, IIRC) - Just wish the guys who were involved could give me an afternoon of chat