Sinclair ZX80 / ZX81 / Z88 Forums

Hello All , nice to meet you!

I'm just getting into these, as well as a few other of my old favourites.. I want to preserve some happy memories of my early computing life.. for a time when nobody remembers what they were like. Also for my son

I just acquired a ZX81 and I've connected it up to a screen using the arial cable, and tuned to pal36. The TV does something (pictured in below video) but from reading around the forum I have 2 questions..

1. Could this be simply an issue with "rear porch" or would that just result in poor viewing rather than these random patterns

2. This is an initial version with the curly lines.. is it supposed to work bare like this or am I missing something like an extra board (I read it had a 'required' extra board)



Video of test

https://youtu.be/PEEd6zelS7g


Thanks in advance! Looking forward to hanging out here !

Hi and you have a lovely machine.

Regarding your queries

1. yes, this effect on the modern telly can be caused by missing back porch in the video signal.

2. when you sort out the video issues, then you can check the ROM version. I think you are a lucky one and your Zeddy is one of early units.

I see, so its worth trying one of these newer video kits, I spotted one for around 10 euro so worth a shot!

So, I think I'm going to try this first;




Is it worth also getting one of these new ULA's ;

https://www.sellmyretro.com/offer/detai ... -ula-32319

It looks like the ULA provides the right video signal anyway so maybe I'll just try that first.

All the chips are soldered on so I'm gonna desolder and put a socket on

Both the CCB and the new ULA creates a usable signal. Only one of them is needed.

Hi,

Not Dead !
Just sleeping...

It's been out of it's small black keyboard case. Compressed air is your friend.

Dishwasher would be better

XavSnap wrote: ↑Tue Mar 05, 2019 12:17 pm Hi,

Not Dead !
Just sleeping...

Aww, a cute furry one!

Hello and welcome to our forum

thedevworks wrote: ↑Mon Mar 04, 2019 9:05 pm 2. This is an initial version with the curly lines.. is it supposed to work bare like this or am I missing something like an extra board (I read it had a 'required' extra board)

The ZX81 was designed to be a very low cost computer, so the built in RAM was only 1k byte. Maybe you are thinking of the 16k byte RAM pack. It connects to the edge-connector at the rear of the machine. These days, there are better alternatives.

The ZX81 you have there is an early one. The date code on the ULA dates it as no earlier than the 11th week of 1981. As they sold well, it would have been sold probably before spring 1981.

thedevworks wrote: ↑Tue Mar 05, 2019 10:34 am So, I think I'm going to try this first;



Is it worth also getting one of these new ULA's ;

https://www.sellmyretro.com/offer/detai ... -ula-32319

It looks like the ULA provides the right video signal anyway so maybe I'll just try that first.

All the chips are soldered on so I'm gonna desolder and put a socket on

Yes, as said above, one or the other, not both.

I have both (but in different machines!).

The ZX8-CCB cleans up the video output from the Sinclar ULA and adds the back porch part of the video signal. It produces a composite video output. It works well as long as the ULA is fully functional.

The new ULA replacement module also works well. It is designed to replace failed ULA chips, but output a composite video output rather than feed a modulator.

Do you any other televisions you could try with it? What works and what does not (in terms of TVs) is a bit random.

Mark