"Different" ZX81's

Discussions about Sinclair ZX80 and ZX81 Hardware
Lardo Boffin
Posts: 1225
Joined: Sat Nov 26, 2016 2:42 am

Re: "Different" ZX81's

Post by Lardo Boffin »

Here is my issue 3. The chips are socketed, but not by me.
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ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
Iss 3 ZXVid
TS 1000 iss 3, ZXPand AY, ZX8-CCB, ZX-KDLX & ChromaSCART
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
Spectrum +2a

Moggy
Posts: 2032
Joined: Wed Jun 18, 2008 2:00 pm

Re: "Different" ZX81's

Post by Moggy »

Looking at some of these issue 3 boards,they seem to have a date code as well next to the ear socket.

Lardo Boffin
Posts: 1225
Joined: Sat Nov 26, 2016 2:42 am

Re: "Different" ZX81's

Post by Lardo Boffin »

And here is another issue 3, not socketed. I bought this in the hope of an easy ULA swap for mine to see if it cures my output issues but sadly it's not looking easy!
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IMG_5260.JPG
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Lardo
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
Iss 3 ZXVid
TS 1000 iss 3, ZXPand AY, ZX8-CCB, ZX-KDLX & ChromaSCART
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
Spectrum +2a

Lardo Boffin
Posts: 1225
Joined: Sat Nov 26, 2016 2:42 am

Re: "Different" ZX81's

Post by Lardo Boffin »

And another issue 3, socketed but different to the first socketed issue 3 of mine above!
IMG_5429.JPG
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It looks like the ROM is in an oversize socket?
IMG_5430.JPG
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This one appears to be producing a rather good image without being composite modded. Once I get the keyboard fixed I will test that in a bit more detail.

Lardo
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
Iss 3 ZXVid
TS 1000 iss 3, ZXPand AY, ZX8-CCB, ZX-KDLX & ChromaSCART
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
Spectrum +2a

Moggy
Posts: 2032
Joined: Wed Jun 18, 2008 2:00 pm

Re: "Different" ZX81's

Post by Moggy »

QUOTE.
"It looks like the ROM is in an oversize socket"?

From the factory any ROM socketed 81's came with a 28 pin socket, your other issue three has been converted by the last owner, I suspect, as issue threes were in the main not socketed possibly as a cost cutting exercise.

The top 4 pin holes on your first issue three are factory soldered over as the 24 pin ROM was directly soldered to the board at the factory.

Lardo Boffin
Posts: 1225
Joined: Sat Nov 26, 2016 2:42 am

Re: "Different" ZX81's

Post by Lardo Boffin »

Moggy wrote:QUOTE.
"It looks like the ROM is in an oversize socket"?

From the factory any ROM socketed 81's came with a 28 pin socket, your other issue three has been converted by the last owner, I suspect, as issue threes were in the main not socketed possibly as a cost cutting exercise.

The top 4 pin holes on your first issue three are factory soldered over as the 24 pin ROM was directly soldered to the board at the factory.
That explains that then thanks!
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
Iss 3 ZXVid
TS 1000 iss 3, ZXPand AY, ZX8-CCB, ZX-KDLX & ChromaSCART
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
Spectrum +2a

Lardo Boffin
Posts: 1225
Joined: Sat Nov 26, 2016 2:42 am

Re: "Different" ZX81's

Post by Lardo Boffin »

An issue one I happened across...
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I like the agricultural feel of the heat sink!
IMG_5485.JPG
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So far I have got an output (dark background not surprisingly) and the keyboard works. Or at least it did until I took the case apart. Fingers crossed it still does when I eventually put it together again!

Not sure whether to composite mod this one or keep it original.

Unusually the case has a serial number 001-003011.

Lardo
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
Iss 3 ZXVid
TS 1000 iss 3, ZXPand AY, ZX8-CCB, ZX-KDLX & ChromaSCART
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
Spectrum +2a

User avatar
Fwapp
Posts: 152
Joined: Mon Jun 01, 2015 10:32 pm

Re: "Different" ZX81's

Post by Fwapp »

Erk - bet that gets a bit toasty! Looks like a good candidate for one of those recom regulators, or one of these - http://www.ebay.co.uk/itm/272451377177? ... EBIDX%3AIT

I get the impression that the SN'ed cases were much later in the ZX81's life, perhaps they used returned/serviced pcb's in them? This is Sinclair we are talking about :lol:
ZX80, ZX81 - 2C158C Bugged Rom iss.1, 2C158C "kludge fix" iss1, 2C184E iss1, 2C210E iss3, US NTSC iss1 "straight traces", US NTSC iss3 TS1000

Lardo Boffin
Posts: 1225
Joined: Sat Nov 26, 2016 2:42 am

Re: "Different" ZX81's

Post by Lardo Boffin »

Fwapp wrote: I get the impression that the SN'ed cases were much later in the ZX81's life, perhaps they used returned/serviced pcb's in them? This is Sinclair we are talking about :lol:
That would explain why a later case contains an earlier PCB. I guess it could have also been the previous owner - the screws holding the PCB in the case are missing.
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
Iss 3 ZXVid
TS 1000 iss 3, ZXPand AY, ZX8-CCB, ZX-KDLX & ChromaSCART
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
Spectrum +2a

User avatar
Fwapp
Posts: 152
Joined: Mon Jun 01, 2015 10:32 pm

Re: "Different" ZX81's

Post by Fwapp »

Also a good chance of that as well :)
ZX80, ZX81 - 2C158C Bugged Rom iss.1, 2C158C "kludge fix" iss1, 2C184E iss1, 2C210E iss3, US NTSC iss1 "straight traces", US NTSC iss3 TS1000

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