Sinclair ZX80 / ZX81 / Z88 Forums

How could I switch between SLOW and FAST mode?

bola_dor wrote: ↑Mon May 24, 2021 1:27 am Just to check... be sure you are not in FAST mode..

No expansion, same problem on several Zx81, can be the Philips Monitor?

Hi all. This is a problem I’ve got with several Zx81 of mine. If a press some keys, sometime the screen ‘lifts up’ showing this horizontal black line. If i reposition slightly the video cable the problem temporary goes off and then goes back. This happens either with composite mod, either without. I...

Hi all! In the past I've already made some mods to Z81s and this time I've tried to make also a 32k internal mod version, but with no luck: I've got a white screen. I've attach the pics hoping you can help me somehow. The composite mod and the Vla81 work very well and I've tried this rom adapter on ...

Thanks!

I’ll read the post and I’ll make the wiring. However, because I’ve ordered several adaptors, do you think they’ll work with Zx81 without modifications?

Thanks!

Thanks Mark!

And what about a 2364 a 2764 EPROM adapter using 2764 for burning Rom (I have many 2764 ROM).

Hi all! I've bought a TL866II Plus Eprom programmer (https://it.aliexpress.com/item/32992209964.html?spm=a2g0s.9042311.0.0.4ade4c4d2HKIbP). What kind of Eprom I need to burn Zx81 Rom? Do I need an adapter? And what about a Rom Switcher? There is an open source project? What Eprom I have to buy to ho...

I don't have it, but I've bought a ULA - I think is the culprit - and when I'll get it I'll update the thread!

Hi! As from the title, I’ve got an untested ZX81 at an ebay auction and I get this boot up screen? What can be the culprit? In the next days I’ll be able to measure with an oscilloscope the ICs, ma my thanks in advance! http://www.terredainventare.it/img/zx81a.jpeg http://www.terredainventare.it/img...

Thanks for your useful explanation! Unfortunately now the Nebulas are out of stock... I haven't been on their site yet. Maybe they speak about emulation because the true schematic is unknown and they Mimik the original behaviour cycle perfect. I wouldn't speak about emulation but about reverse engin...