Time to go back in time again - ZX80 replica build

[rubber_jonnie]

Using my worst Paint skills I did a quick edit to the one in the middle:

Edited.jpg

So essentially inverting what was there. Definitely not back porching correctly as the two either side are what it actually looks like.

[rubber_jonnie]

OK, so I took the board out of the modulator can and swapped the transistors for what the original design called for and then did another lash up:

IMG20250927145230.jpg

Which included a transistor mod on the output side. Interestingly I now get a better looking signal:

IMG20250927150402.jpg

Blue is input from the ZX80, yellow is the output side of the mod board. There is some back porch now, and I am almost getting an image, it's slightly better than before, but not quite there. Also odd is that the original signal from the ZX80 appears to have a very minimal back porch, which I'd not noticed before.

The seller has given me both a refund and sent another board, which is amazing and I'm very grateful for such a brilliant response.

After several recommendations I have ordered a ZX8-CCB, so we'll see how that pans out when it arrives.

[rubber_jonnie]

OK, so the ZX8-CCB is in the post, lets hope it's the answer I am looking for. It's coming from Germany so may take a little while to arrive.

[rubber_jonnie]

Just had an email that the ZX8-CCB will be arriving today, so hopefully I can put this project to bed in time to bring it to CL4 :)

[HigashiJun]

:crossed1:

[rubber_jonnie]

Well, Royal Mail, more like Royal Fail!!

No ZX8-CCB yesterday, and the letter post has been super erratic, though my wife actually had a next day delivery parcel arrive on time via Royal Mail yesterday.

Really don't get why the post has gone to :shite: again...

[HigashiJun]

Oh no...

I was expecting some good feedback from you today.

:(

[rubber_jonnie]

Oh no...

I was expecting some good feedback from you today.

:(

I was hoping I could give some...

[rubber_jonnie]

Well it seems my moan worked and a bunch of post arrived today, including the ZX8-CCB which I hooked up immediately:

IMG20251004145814.jpg

Whilst it's a step forward, something is still wrong. After a bit of adjustment I get a nice clear white background

IMG20251004145853.jpg

But no K cursor. Video signal is nice and I have a good back porch. Yellow is the output from the ZX8-CCB, blue is the input from the ZX80 into the Z8-CCB

It's more of a signal than I've had before, and I think the machine is working fine based on my earlier findings. I will swap out the RAM for know good in my OSI 600, but I don't think that's the problem, so next up I need to have a good look at the video circuit.

IMG20251004153935.jpg

IC's 11, 12,13 and 20 seem to be the main protagonists so I may just pop them in the TL866 to see if they are all good.

EDIT: All the IC's test fine...

[HigashiJun]

Oh bugger !

This issue seems to be really tough...

Hope you will find soon what's going on there.