"Different" ZX81's

[1024MAK]

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

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

[Moggy]

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

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]

Argh. I have changed the caps thus far but that’s it. 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.

[gammaray]

I hope it is with a switching regulator that does not generate heat...

[Lardo Boffin]

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.

[wjsteele]

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:

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Bill

[1024MAK]

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

[Moggy]

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]

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

[1024MAK]

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