Sinclair ZX80 / ZX81 / Z88 Forums

Fire me an private message if interested.

Cheers
Phil

Ok, I spoke a little too soon. After about 20 seconds the pixels started to creep. Adding a capacitor to GND helped fix this (as Pokemon suggested) Fortunately it works well in the issue 3, but unfortunately not in my issue 1 where the characters are still all weird. So It'll stay in the issue 3. IM...

I was just trying out the thought about touching the ROMCS line, unfortunately it didn't seem to work....However while doing this I had another serendipitous moment. The lead going to pin 6 of the 74LS02 dropped off, and the 'K' cursor instantly cleared up. Then I connected this line to GND and agai...

I just built up Marks circuit using a 74LS02.
Have a look at this...It's even more dynamic

https://www.youtube.com/watch?v=zg1Gymf ... e=youtu.be

Phil

Me again,
I tried 2 things:
1) plugged in the ZXpand. It looked perfect...

2) plugged in the keyboard with no ZXpand...

Hi guys, So I connected the ROM CS line to the 680 Ohm resistor instead of directly to the ROM pin 20. This helped, now I can connect GND to the 74LS32 and still get the cursor. In fact the 'K' cursor first appears perfectly formed, then after a few seconds pixels start to flicker off. Strangely thi...

Yes, very strange indeed.
Here is a pic of the cursor without the GND line attached to the 74LS32.
Sometime it looks more formed than this, and other times worse.

As I mentioned previously, if I connect the GND line up then the screen become blank again.

Phil

Just racing out the door, but wanted to get this out there quickly. Firstly thanks for the great ideas. I quickly built Andy's circuit using jumper wires, and lifting pin 13 in the ULA. At first it didn't work...still a blank white screen. Then I accidentally knocked the GND wire off the 7432 and I ...

Hi Andy,
Can you briefly explain how that would be hooked up?

Cheers

Philip

Thanks again for the reply.
Would something like this work?
One question.
If the issue is the CS line, would installing the ZXpand (with it's own copy of the ROM) fix this, or does it still rely on the CS line from the ULA for it to work?

Cheers