ZX81 packaging

[msellan]

Ok as promised

Here are pictures of the circuit board front and back, a close-up of the ICs and a couple of general pics of the kit and parts.

zx81circuitboardcomponentside.jpg

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zx81boardsolderside.jpg

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kit.jpg (98.89 KiB) Viewed 3654 times

What do you think? The board is one I've only seen here. Even my issue one US zeddy has the straight traces and not the curvy ones. What about the ULA, ROM and CPU? The ROM looks generic. My 80s and 81s both have "Sinclair Research" printed on them. And I think the CPUs in my other ZX machines are Zilog brand. I knew NEC made a version but don't know anything about when they were being used by Sinclair. As for the ULA - that's still quite a mystery to me as to versions, etc.

Best,

-mark

[Moggy]

Nice kit very nice indeed.

Is it a trick of the lens or are all those holes soldered over?

The board looks like a very early issue one hence the "hand drawn" look.

As for the chips The ULA # 2C210E is the last of the line and more importantly has the back porch missing from the previous incarnations. (# 2C158E 2C184E)

The NIPPON ELECTRIC CO CPU is the one most commonly found in the Sinclair products that used Z80's alongside a smattering of SGS-THOMSON and MOSTEK devices.

The ROM is the first of what I suspect is a MOTOROLA chip I have ever seen so possibly quite rare,apart from the Sinclair branded ones I have the most common I have had in my collections over the years has been manufactured by MOSTEK.

The two RAM chips also seem to bear the MOTOROLA insignia.

Many thanks for sharing this excellent kit example.

[Lardo Boffin]

The ROM is the first of what I suspect is a MOTOROLA chip I have ever seen so possibly quite rare,apart from the Sinclair branded ones I have the most common I have had in my collections over the years has been manufactured by MOSTEK.

There are two photos of what look like Motorola ROMs on the Different ZX81s thread, page 4!

Lardo

[1024MAK]

As Moggy said, that PCB is a ZX81 issue 1. There was no issue 2. The other two versions were a issue 3 and the Timex board (similar to the issue 3).

What is strange is that the issue 1 board was supplied well after the manufactured ZX81s were being produced using issue 1 boards. And the most recent date code on the chips indicates the kit was put together well into 1983 (no earlier than the second week of March, 1983)

Mark

[msellan]

Nice kit very nice indeed.

Is it a trick of the lens or are all those holes soldered over?

The board looks like a very early issue one hence the "hand drawn" look.

As for the chips The ULA # 2C210E is the last of the line and more importantly has the back porch missing from the previous incarnations. (# 2C158E 2C184E)

The NIPPON ELECTRIC CO CPU is the one most commonly found in the Sinclair products that used Z80's alongside a smattering of SGS-THOMSON and MOSTEK devices.

The ROM is the first of what I suspect is a MOTOROLA chip I have ever seen so possibly quite rare,apart from the Sinclair branded ones I have the most common I have had in my collections over the years has been manufactured by MOSTEK.

The two RAM chips also seem to bear the MOTOROLA insignia.

Many thanks for sharing this excellent kit example.

Sorry the pictures of the board are deceptive. I wanted you all to be able to have a really clear view of the traces and my iphone takes such crappy pictures in dark spaces that I scanned the board with a flatbed scanner. So the holes are not soldered over just reflected in a weird way that makes them look filled in.

It's really interesting to hear that there's a late ULA paired with such an early board. Is the ROM, albeit uncommon, early or late? Will it have the famous square root bug? At this point I'm sure I won't build the kit, so it's just curiosity. When I bought it these kits were in plentiful supply so I had planned to build it but now they seem pretty uncommon so I can't bear to spoil it. Maybe I can find someone with a nice issue 1 ZX80 to trade with.

As Moggy said, that PCB is a ZX81 issue 1. There was no issue 2. The other two versions were a issue 3 and the Timex board (similar to the issue 3).

What is strange is that the issue 1 board was supplied well after the manufactured ZX81s were being produced using issue 1 boards. And the most recent date code on the chips indicates the kit was put together well into 1983 (no earlier than the second week of March, 1983)

Mark

Wow, yes that's interesting. I bought the kit from this guy: http://www.zebrasystems.com/nyc/index.p ... x-sinclair and here is the story on his website about why he was selling the kits: http://www.zebrasystems.com/nyc/index.p ... -kit-story My recollection is that I bought the kit much earlier than 2012 and it was fairly cheap. I think I paid $59.95 which also included a 16K Memopak. I really did almost buy two but thought I'd build one first and the later I'd pick up another. But I never did. Of course for all the crazy computers I spent money on in the 80s I could have bought this kit over and over.

Best,

-mark

[Lardo Boffin]

Is the ROM, albeit uncommon, early or late? Will it have the famous square root bug?

I think I paid $59.95 which also included a 16K Memopak. I really did almost buy two but thought I'd build one first and the later I'd pick up another.

My bugged ROM is shown below. It's an NEC - not sure if these were the only bugged ones? Am sure someone will have one if there were other ROMs affected. The date stamp on yours in 8306 so that's the 6th week of 1983 and therefore quite late on I think. My bugged one has 1980 / early 1981 date stamps.

viewtopic.php?f=7&t=2153&start=87

$59.95? Budget 10 times that now... Wish I could afford one!

Lardo

[1024MAK]

All but one of the chips are from 1983. The Z80 CPU (marked D780C) is week 34 in 1982.
The earliest ZX81's have chips with date codes for the early part of 1981.
By 1983, sales of ZX81's were falling, as the Sinclair Spectrum had became the best selling computer in the U.K.

Mark

[Lardo Boffin]

Full house there Lardo You've got the lot!!

(Except the perfect bound 212 page 2nd reprint)

Just got a second edition, first reprint, perfect bound with 212 pages! So still have one to go...

[Fwapp]

Full house there Lardo You've got the lot!!

(Except the perfect bound 212 page 2nd reprint)

Just got a second edition, first reprint, perfect bound with 212 pages! So still have one to go...

But is that the Richard Clay print or the Leagrave Press print? Down the Rabbit hole we go.....

One of the chaps on the FB groups figures there were 5 or 6 different printers for the ZX Spectrum manuals for one of the editions, I'm sure someone will be hunting them all.

[Moggy]

Full house there Lardo You've got the lot!!

(Except the perfect bound 212 page 2nd reprint)

Just got a second edition, first reprint, perfect bound with 212 pages! So still have one to go...

Of which I have the only copy sooooo ebay £2000 methinks (on near offer)

HE HE keep at it Lardo nearly there.