Newbie question - ZX81 Issue 1 board

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hanger312
Posts: 3
Joined: Sun Jan 15, 2023 5:42 pm

Newbie question - ZX81 Issue 1 board

Post by hanger312 »

Thanks for letting me join the forum.

Got a ZX81 issue 1 dated 1980 (1st ZX81 came out in March 1981)
(3 photos attached)

I've got a few questions you might be able to shed light on (referring to the photos).

1) The board predates the original launch date which makes sense and it has hand traced etching. So is it an original version 1 ZX81?

2) The main chips are socketed. Was this normal for the issue 1 or is this
a kit version? (which I suspect).

3) The ROM chip has a Malaysian stamp on it. I thought the originals were
from Sinclair Reasearch?

4) The Ferranti ULA is numbered 8142. I haven't seen an earlier version
number. Is it also one of the 1st ULA's?

5) The last question is - Is it possible these have been replaced later?


From what limited knowledge I have it looks like it was never opened
before. The soldering on the base looks consistant except one or two areas.
(see photo).

I did the composite video MOD which you can see. It works
perfectly with excellent image quality even on a 60 inch TV. It came with
an original 16K Sinclair Research RAM pack and power supply.
All working and tested perfectly.

Thanks.

Graeme Hanson.
Attachments
Board_underside
Board_underside
Date mark
Date mark
Board_topside
Board_topside
Last edited by 1024MAK on Sun Jan 15, 2023 10:10 pm, edited 1 time in total.
Reason: Edited to remove redundant image tags
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1024MAK
Posts: 4366
Joined: Mon Sep 26, 2011 10:56 am
Location: Looking forward to summer in Somerset, UK...

Re: Newbie question - ZX81 Issue 1 board

Post by 1024MAK »

hanger312 wrote: Sun Jan 15, 2023 9:09 pm Thanks for letting me join the forum.
Hello and welcome Graeme :D
hanger312 wrote: Sun Jan 15, 2023 9:09 pm Got a ZX81 issue 1 dated 1980 (1st ZX81 came out in March 1981)
The date on the board is only the date when the track layout and the solder resist was designed, not the date when it was actually manufactured.

A better date for when the board was made, is the latest date code on the modulator (that has the TV output) or on the ULA, the Z80 or the ROM chip. On your board, it looks like the ROM has a date code of 8147, which means the 47th week of 1981. The Z80 has a date code of 8143, so week 43 of 1981. The ULA is 8142, so week 42. So this board was assembled sometime at the end of November 1981, or later. Maybe even early 1982.
hanger312 wrote: Sun Jan 15, 2023 9:09 pm 1) The board predates the original launch date which makes sense and it has hand traced etching. So is it an original version 1 ZX81?
Yes, it’s an issue one board, hence why it says this on the board. See above for a guide on dates.
hanger312 wrote: Sun Jan 15, 2023 9:09 pm 2) The main chips are socketed. Was this normal for the issue 1 or is this
a kit version? (which I suspect).
It’s not always easy to tell, as the times when sockets were used and the number used varies wildly across the production run. The only chips that were almost always soldered direct were the SRAM chip(s) (which are soldered on your board). So your board is fairly normal. If the soldering is uneven, or there are bits of honey/brown coloured flux left behind, then it’s likely to be a kit built unit. But from your photos, it looks like it was wave soldered in a factory.
hanger312 wrote: Sun Jan 15, 2023 9:09 pm 3) The ROM chip has a Malaysian stamp on it. I thought the originals were
from Sinclair Reasearch?
It depends on which supplier had stock at the time. For a lot of the parts, multiple suppliers were used. A lot, not all have Sinclair Research labels. Occasionally EPROMs are found as well. Remember, Sinclair Research did not make the computers. They supplied the data to the chip manufacturer and they then made the ROM chips. Then Timex built the boards and put them in the cases.
hanger312 wrote: Sun Jan 15, 2023 9:09 pm 4) The Ferranti ULA is numbered 8142. I haven't seen an earlier version
number. Is it also one of the 1st ULA's?
No, that’s a 2C184E ULA, which is the second of three versions. I explain the date code above.
hanger312 wrote: Sun Jan 15, 2023 9:09 pm 5) The last question is - Is it possible these have been replaced later?
Yes, but it’s unlikely given the three major chips have similar date codes.

Look at the date code on the label on the modulator, that will help.

Mark
Moggy
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Joined: Wed Jun 18, 2008 2:00 pm

Re: Newbie question - ZX81 Issue 1 board

Post by Moggy »

Just to add to Marks answer, the ROM pictured is a Mostek device and alongside ones supplied by NEC and Motorola is a common one. I'm almost sure I've spotted an Hitachi one in the wild too as well as the rare Texas Instruments EPROM that was used when chip supplies were short.

I'm fairly certain that the ROM chips sporting the "Sinclair" name were NEC supplied devices also.
hanger312
Posts: 3
Joined: Sun Jan 15, 2023 5:42 pm

Re: Newbie question - ZX81 Issue 1 board

Post by hanger312 »

Wow, I wasn't expecting such an in depth response 1024MAK.
That's brilliant. I didn't realise the chip nos. were set out that way.
I know from watching videos that Sinclair were clever in buying
chips on the cheap. I will check the modulator cap. I had already done
the MOD before I took the photos. I didn't know the date details
were embedded in the code printed. I will check later
and maybe post a photo.

So it's only 41 years old at it's worst. Crazy.

MOGGY too, thanks for your comment.

Couple of photos of the output on my tv/monitor. Not the 60 inch one.
Distortion only from the camera refresh rate. Absolutely clear as a bell
to the normal eye.

Thanks again guys.
Attachments
POKE 16K MEM RESULT
POKE 16K MEM RESULT
POKE MEM PROGRAM
POKE MEM PROGRAM
Lardo Boffin
Posts: 1880
Joined: Sat Nov 26, 2016 2:42 am

Re: Newbie question - ZX81 Issue 1 board

Post by Lardo Boffin »

If you want to see a few pictures of various zeddies there are some here:

https://sinclairzxworld.com/viewtopic.php?f=8&t=3312


Also as yours is a beige topped board here are my musings on that. :D

https://sinclairzxworld.com/viewtopic.p ... 236#p47236
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
hanger312
Posts: 3
Joined: Sun Jan 15, 2023 5:42 pm

Re: Newbie question - ZX81 Issue 1 board

Post by hanger312 »

Thanks LARDO. Much appreciated. I am among friends :)

I was a nerdy 11 yr old in 1981. Glad in retrospect!!
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