"Different" ZX81's

Discussions about Sinclair ZX80 and ZX81 Hardware
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1024MAK
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Re: "Different" ZX81's

Post by 1024MAK » Fri Nov 03, 2017 3:33 pm

Lardo Boffin wrote:
Fri Nov 03, 2017 3:21 pm
Is the M for Motorola?
In that style, yes.

No, I think it's best you leave that one as it is (assuming it works okay).
And yes, the ceramic chips with the gold coloured detail do look smart 8-)

Would be interesting to see which ROM version code that ROM chip contains.

Also SGS Z80 CPUs don't appear to be that common in Sinclair machines (or, I should say, I've not see many myself, maybe others have seen them more often?)

Mark

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Re: "Different" ZX81's

Post by Moggy » Fri Nov 03, 2017 4:06 pm

1024MAK wrote:
Fri Nov 03, 2017 3:33 pm
Lardo Boffin wrote:
Fri Nov 03, 2017 3:21 pm
Is the M for Motorola?
In that style, yes.

No, I think it's best you leave that one as it is (assuming it works okay).
And yes, the ceramic chips with the gold coloured detail do look smart 8-)

Would be interesting to see which ROM version code that ROM chip contains.

Also SGS Z80 CPUs don't appear to be that common in Sinclair machines (or, I should say, I've not see many myself, maybe others have seen them more often?)

Mark
I concur with Mark, leave it be as it's a good one for the collectors.

As for CPUs NECs or mainly Zilogs is my experience with the Italian jobbies amounting to a grand total of one(which I still have) in thirty odd years of messing with zeddies, a good little find there Lardo.

Lardo Boffin
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Re: "Different" ZX81's

Post by Lardo Boffin » Fri Nov 03, 2017 5:27 pm

Argh. I have changed the caps thus far but that’s it. :oops: I was going to replace the regulator and fit a ZX8-CCB. I will put that on hold.

If anyone is interested in taking ownership I only paid £9 for it so happy to pass it on for similar plus p&p.

I connected a test zx8 to it and it produces a lovely picture.
ZX81 iss 1 (bugged ROM, kludge fix, normal, kit)
Iss 3 with ZXVid, another in nearly perfect box
TS 1000 iss 3, ZXPand AY, ZX8-CCB & ZX-KDLX
TS 1500
TS 2000
Spectrum 16k (iss 1 s/n 1499)
Spectrum 48k
Toastrack + DIVMMC future

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gammaray
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Re: "Different" ZX81's

Post by gammaray » Sat Nov 04, 2017 1:14 am

I hope it is with a switching regulator that does not generate heat...
Finish what you start. Truth is over the mountaintop or six feet under.
4 x TS1000, 2 x TS1500 , 2 x timex 2040 printer, 1/2 x timex 2020 cassette deck, ZXPAND, ZeddyNET, ZXBlast..., unfinished Spectrum...Still no life!

Lardo Boffin
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Re: "Different" ZX81's

Post by Lardo Boffin » Sat Nov 04, 2017 9:10 am

gammaray wrote:
Sat Nov 04, 2017 1:14 am
I hope it is with a switching regulator that does not generate heat...
Of course! But it is on hold as it looks like it might have a new owner. :D
ZX81 iss 1 (bugged ROM, kludge fix, normal, kit)
Iss 3 with ZXVid, another in nearly perfect box
TS 1000 iss 3, ZXPand AY, ZX8-CCB & ZX-KDLX
TS 1500
TS 2000
Spectrum 16k (iss 1 s/n 1499)
Spectrum 48k
Toastrack + DIVMMC future

wjsteele
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Re: "Different" ZX81's

Post by wjsteele » Sat Nov 04, 2017 3:43 pm

As a side note... the Issue 1 US board on my ZX81 has a different RF Modulator... in fact, it has a Channel 3 and 4 selector switch on it instead of the standard 2 and 3. (Mine is dated a few weeks earlier as well, being the 28 week of '81.)

See here:
IMG_20171104_112639.jpg
IMG_20171104_112639.jpg (1.46 MiB) Viewed 145 times
IMG_20171104_112559.jpg
IMG_20171104_112559.jpg (1.48 MiB) Viewed 145 times
IMG_20171104_112906.jpg
IMG_20171104_112906.jpg (2.34 MiB) Viewed 145 times

Bill

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1024MAK
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Re: "Different" ZX81's

Post by 1024MAK » Sat Nov 04, 2017 5:25 pm

Thanks for the photos and info Bill.

I was not aware that ZX81/TS1000 computers with more than one set of channels were sold.

In the U.K. the only TV transmissions on VHF were the B&W 405 line system. Our 625 line service was only available in the UHF band, so nearly all 1980s computers, video players/recorders etc all used UHF channel 36 (as this channel was the only one that was free of television transmissions across the country). Hence no channel selection switch on UK ZX81's.

Mark

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Re: "Different" ZX81's

Post by Moggy » Sat Nov 04, 2017 6:52 pm

1024MAK wrote:
Sat Nov 04, 2017 5:25 pm
Thanks for the photos and info Bill.

I was not aware that ZX81/TS1000 computers with more than one set of channels were sold.

In the U.K. the only TV transmissions on VHF were the B&W 405 line system. Our 625 line service was only available in the UHF band, so nearly all 1980s computers, video players/recorders etc all used UHF channel 36 (as this channel was the only one that was free of television transmissions across the country). Hence no channel selection switch on UK ZX81's.

Mark
I was aware of this on US 81's and I'm sure it had something to do with local TV transmitters upsetting the zeddy, if you got interference on one channel you used the switch underneath to switch to another frequency but I'm open to correction obviously.

EDIT.

From what I gather from the TS1000 manual apparently local transmitters would broadcast on either CH 2 or CH 3 so to watch TV if the transmitter broadcast on say CH 2 you would set your TV to the same channel, to use the computer you would set the TV to the channel not being broadcast upon, in this example CH 3, and set the switch under the zeddy likewise so as not to have the TV broadcast interfering I would assume.

wjsteele
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Re: "Different" ZX81's

Post by wjsteele » Sat Nov 04, 2017 8:01 pm

That's correct, we had a local channel 2 so we always used 3 for computers... but this ZX81 is rather rare in that it has a 3/4 selector instead of the normal 2/3 selector. In fact, it's the only one I've personally ever seen. All TS1000 machines were 2/3.

It's a very first generation US model... and amazingly enough, the keyboard has not deteriorated at all AND the ULA actually still works!

Bill

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1024MAK
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Re: "Different" ZX81's

Post by 1024MAK » Sat Nov 04, 2017 8:08 pm

Sorry, I may not have been clear. I know about the VHF channel 2 or channel 3 selection switch. What I meant was that I did not know that other versions existed with a choice of a modulator that had a channel 3 or channel 4 switch (like in the photo earlier in this thread)...

Mark

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