Sinclair ZX80 / ZX81 / Z88 Forums

Hi, I got the Z80 Replica Kit selling on eBay, from Bulgaria. It took 3 weeks to arrive ! It is a very nicely presented and clean kit. As always happens with any kit, it is a shame to assemble it! :-) I miss having a case though. Anyone with a 3D printer wanting to take the challenge to print a ZX80...

Thanks everyone to point out possible checkings. I will try to check it all. However, having replaced every active component (every chip and the two transistors), is it not strange I get exactly the same behavior than using the original components ? I mean, would it not point to some passive compone...

Here a ZX81 with ULA 82-45. No serial number.

Tried with 16K pack. No changes.

I have taken a look at the thread where pokemon explains the shape I should get on A15. I get a similar pattern to the one in the pictures for a couple of seconds. Then the signals starts changing. Some seconds later the signal is flat. So it seems clear to me that some component is heating up and t...

gozzo, I have replaced both TR133 with new ones. No way. Same white display!

iturbez, I will check RAM connections and will take a look at these scope signals too. Thanks!

I have checked the NMI.
It is alive for a couple of seconds and then vanishes.
The edge an frequency of the NMI pulse matches the start video signal. Is this right? The pulse is 5us wide.
I can figure out the NMI should last forever, unless fast mode is used, right ?

I have not replaced the ROM because apparently it reads well and the code matches the one I can see on the available ZX81 ROM listings. I do know the system is working because I see it working when I connect it to a Z80 ICE. I can actually see the startup code running. The TV modulator appears to wo...

I am trying to get to life my old ZX81 in kit. Apparently it is working but display is white. No cursor, no characters. Just a white background. I have checked the video output with a scope and it looks right. The display is a well formed white rectangle. The Z80 apparently is running fine. I have c...

Of course, I am not interested in machines that work at first try!
Said this, I do not like these opaque soldering mask. I prefer the transparent ones.

inaki.