Sinclair ZX80 / ZX81 / Z88 Forums

When you say no video, do you mean black screen, or white screen with no “K”? Is this a different tv from before when it was working? Adrian has a few cheap scopes on his channel - I have the Hantek 6022BE one - I think in later videos he found a better one. What is the voltage of the outer most wir...

I swapped the ula and it didn’t seem make a difference - I tried pushing and twisting on the ula to see if that would make any difference - no change - still corruption on the screen. If anything it is a bit worse now after the swap. I might try replacing the socket in the weekend to be sure. Genera...

I have see some screen corruption when doing the operations on memory scanner. The display was corrupted in patches Ula is socketed and I do have a working spectrum that I can swap with Z80 is not socketed. I’ll try An inspection around my recap points the ula swap And then a reflow It does feel lik...

I have a 48K issue 4B On the retroleum diagnostic rom, “test code execution in upper ram” reports an error pretty quickly (within a second of it running) The memory tests all pass fine through many iterations. I’ve also tried the ZX Diagnostics rom. One time it failed on the ZX Spectrum Diagnostics ...

Martin - I look forward to hearing about how the video works out. I thought about going that route, but since I have an RGBtoHDMI already for my Beeb, I ended up feeding the signal into that. Its super sharp, but due to the price of an RGBtoHDMI, I wouldn't recommend this approach. (But if you had a...

Just a minor addition.

I just reconfirmed that WESPI doesnt work with an OS Rom v550
You put in the 649 version and it works.

I've also tried the SN7450 idea above - it did not work (I assume more timing issues). So it seems that the result is: Use a capacitor if you can. Simplest approach. (Ive seen 33pF to 100pF work depending on the board Ive tried it on) If a capacitor doesnt work for you, try a 74HC00 logic gate - it ...

Nice!

Doh! Why didn’t I see that logic equivalency!

So I tried this out with the SN74LS00 and it doesn’t work - I think there are speed issues.

But trying with a SN74HC00 does work for me. Nice!

Thanks Mark, What would it look like with just two NAND gates? I think I need 3 (one to mimic a NOT, and two to mimic an AND) Question: I initially tried without the “no-op OR” (ie after the A14 NAND) but it didn’t instantly work and it felt like for timing purposes, I had to have the same number of...