Sinclair ZX80 / ZX81 / Z88 Forums

@gozzo: send me a PM.

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128K edition nearly finished

Finally have partly built the Zx Max 48, but when powered up i get a weird display

i dont have the surface mount AD chip fitted, im running off the rgb.

what is the minimum cable wiring for rgb, i dont have all the grounds connected in the scart plug, only one connected to pin 18.

Can anyone help with the display i have.

What make of the inverter (7404) do you have? The clock signals generator works much better with HCU series instead of HC. Personally I would recommend Philips, NXP or Toshiba chip in this application. TI make 74HCU04 is not hassle free. I've tested a few of them.

I've swapped out the 7404 for a 74HCT04 from my spare clock board of a RC2014 setup. Same picture.

My 62256 rams are 100 speed and not 55 would this make a difference.

I took out the zx rom and still have the same picture.

I'll list out all the ic's and makes.

It works with 100ms RAM chips. I have them in my ZX Max 48K board. I think that in your case you are facing issues with the 14MHz clock, because the horizontal synchronisation is lost.

I also had an issue with one of the clocks, but in my case it was the 4.43MHz clock used for the colour timing. I used an 74HCU04 (the same as used on the +2 if I remember correctly).

http://blog.tynemouthsoftware.co.uk/201 ... ax-48.html

If the 14Mhz isn't running, that might explain it because the Z80 clock is divided down from that as well.

Ive completely replaced all the ic's except the cpld. I'll try the 14mhz crystal as you said.

I did not say that was anything wrong with the crystal. The type of the 7404 inverter is critical. You should try to install there 74HCU04 instead of either HCT or HC.

Ordered some Philips 74HCU04's