Sinclair ZX80 / ZX81 / Z88 Forums

The ULA is, if I understand correctly, basically a collection of logic gates in one chip, so it's possible for it to partially fail without completely breaking down... if that makes sense. That does make sense - I have some ‘danger ULAs’ that are part failed that I keep for test purposes. It doesn’...

I put a different ULA in and it works perfectly. Put the old one in and back to Venusian.

Any ideas how a ULA could do this? Given that it pretty much works fine when a RAM pack / Spand is plugged in?

Guess the program!


Running through the ChromaSCART.

The ROM is really quite hot to the touch.

In the spirit of quick checks I have plugged in my ChromaSCART. With the onboard RAM switched off I get the display issue. With the onboard RAM switched on I still get the display issue. I was expecting it to work properly with the RAM on as this is in effect the same situation as having a RAM pack ...

I recall, along time ago, that I had a similar problem and replacing the voltage regulator fixed the problem. I got this idea from a forum posting but I can't find it. Not being a hardware guy I have no idea why the voltage regulator would garble the display, but replacing it worked for me. Regards...

It arrived like this yesterday. Sold as untested (as usual).

I haven’t had time to get technical yet - just a few minutes to try some high level stuff at lunch time.

Hopefully when the kids are in bed…

Don't forget, with 16K bytes of RAM, you get a fully expanded display file, and it can be in a different position in RAM. Have you tried changing the ULA? Mark I will be looking for a spare later on thanks. If I type in a program that takes up most of the 1K and it doesn’t corrupt would that prove ...

I will check inside the keyboard sockets just in case but it does the same with just the Memotech keyboard connected.

It loads and plays the games that I have tried. Although the screen is suitably garbled.

This is what I get when I type all of the keys: