"Different" ZX81's

[Tezz]

I don't think I have any unusual boards wthin the ten ZX81's that I've now bought. That issue 3 board posted above looks the same as the one I just bought albeit with different RAM. Mine wasn't functional so I've removed the modulator for another board which is now working. The issue 3 board was still non-functional with the RAM pack plugged in so I've started carefully removing the ICs for testing. Interestingly the ULA has "STI PHIL" on the underside, I've not seen that on any of the other ULAs.

Issue 3 board

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ULA removed

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ULA IC

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ULA underside

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[Lardo Boffin]

That's a cool ULA!

Lardo

[Moggy]

The PHIL marking I believe denotes manufacture in the Philippines as opposed UK,Though it would probably need Mark or one of the other techies to confirm that.

I also wish my boards were as pristine as that.

[PokeMon]

In general for me it looks a bit like a chinese (or philippine) copy.
See the distance, line position and torsion of each single letter.
Looks crazy, nearly hand branded.

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[1024MAK]

Back then, it's possible that the printing device did use hand typeset characters

Mark

[Tezz]

Oops yes I forgot also to mention the misaligned lettering. Sadly it tested bad in a working board today.

[msellan]

I'm not sure if this constitutes interesting or not but it might add to your information collection. Here is my US issue1 ZX81 as it came to me from Sinclair. I'm the original owner and it's never been modified or repaired (although it also no longer works and thus needs to be repaired)

It has a small factory mod on the back and the case has a serial number. I included the ULA in the case/serial# picture just for good measure.

Best,

-mark

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[gammaray]

My US #1 board does not have that mod... Maybe a bad trace?

[msellan]

Interesting! I'll take a closer look tomorrow. But if it is a bad trace that means Sinclair sent me a hacked computer long before that word was even a term! I didn't notice if the resistor they added on the back is the same value as the one on the front. I'll take closer look tomorrow.

Unfortunately, the ground strap there where the strap and purple resistor wire are connected have come loose from the board. I should remedy that first. I plugged it in to the PS the other day to see if I could get anything but no luck. It's like there's no power getting to anything. Maybe the voltage regulator is shot? I'll need to get a meter on it, I guess. I'd like to get it working again since it's the original unit I had as a kid.

Thanks for the tip!

Best,

-mark

[Moggy]

The ULA pictured here lacks what is known as a back porch signal(type back porch into the search box for lots of discussions) and in my very crude simplistic way of describing things it basically means it will only play ball with old CRT black and white TV's and some CRT colour TV's albeit with a very dark picture on these colour sets.

If you have connected it to a newer LCD or LED type set then it may not show any picture at all but is working nevertheless.

Forgive me if this is something you were already aware of.