Sinclair ZX80 / ZX81 / Z88 Forums

Well I am not sure why but my Sinclair has decided to shape up and fly right. :D I have had it running for several hours now with no problems. I really didn't do anything other than leave it on for quite a while and the artifacts stopped. I have let it cool down and start again with no issues. Reall...

Yes, this is a US computer.

Andy is going to send me a new ULA. Hopefully it will solve the problem.

zx-heinz wrote: ↑Sat May 04, 2019 3:03 pm Check, if the oscillator frequency (at Pin 6 CPU) is stable at 6.5MHz. Could you replace the ULA?

Its is nice and steady at 3.25mhz. Should it be as 6.5mhz?

Neither of my original ULAs work (210 and 184). I have Andy's ULA installed.

Do you have other chips from other zeddies you can try in it? It would probably be worth being certain the Z80 and ROM are ok. Yup. I tried that already. Same result. Something new however. I just left it on and and now I am getting long periods (20-40 seconds) of normal operation and then back to ...

Here is another picture. You can see the video signal spacing is random. On one scan line you can see where the 'K' is generated and then another scan line doesn't finish before it starts again.

At least that is what I (as a noob) see.

Sean

How much ripple is on the 9V PSU output and what voltage do you get? Same question, but on the +5V rail. Both can be tested on the pins of the 7805 voltage regulator, just be careful not to short anything out. Mark PSU output is 11.3V The 5V rail is right at 5V. Both Voltages have no ripples. Both ...

Here are the videos.

So I bought a TS 1000 and found the ULA was dead. I did the composite mod and the internal 16K memory upgrade. I bought Andy's ULA and everything worked! (for a little while). The first time I used it I had it on for about an hour and had it running a math problem. It worked great. Later though it s...