zx spectrum in zx81 case

McKlaud
Posts: 147
Joined: Tue Dec 19, 2017 10:02 pm
Location: St Albans, UK

Re: zx spectrum in zx81 case

Post by McKlaud » Sat Feb 03, 2018 5:59 pm

@gozzo: send me a PM.

-------------------------

128K edition nearly finished
Attachments
ZXMax128_01.jpg
ZX Max 128
Claudius
----------

Retrogadgets
Posts: 9
Joined: Wed Jan 29, 2014 8:29 pm
Location: Sheffield, UK

Re: zx spectrum in zx81 case

Post by Retrogadgets » Fri May 04, 2018 1:55 am

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.

Retrogadgets
Posts: 9
Joined: Wed Jan 29, 2014 8:29 pm
Location: Sheffield, UK

Re: zx spectrum in zx81 case

Post by Retrogadgets » Fri May 04, 2018 2:06 am

WP_20180504_00_09_27_Pro.jpg
WP_20180504_00_08_25_Pro.jpg

McKlaud
Posts: 147
Joined: Tue Dec 19, 2017 10:02 pm
Location: St Albans, UK

Re: zx spectrum in zx81 case

Post by McKlaud » Fri May 04, 2018 8:38 am

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.
Claudius
----------

Retrogadgets
Posts: 9
Joined: Wed Jan 29, 2014 8:29 pm
Location: Sheffield, UK

Re: zx spectrum in zx81 case

Post by Retrogadgets » Fri May 04, 2018 10:11 pm

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.

McKlaud
Posts: 147
Joined: Tue Dec 19, 2017 10:02 pm
Location: St Albans, UK

Re: zx spectrum in zx81 case

Post by McKlaud » Fri May 04, 2018 11:02 pm

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.
Claudius
----------

tynemouthsoftware
Posts: 2
Joined: Wed May 31, 2017 9:40 am

Re: zx spectrum in zx81 case

Post by tynemouthsoftware » Fri May 04, 2018 11:11 pm

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.

Retrogadgets
Posts: 9
Joined: Wed Jan 29, 2014 8:29 pm
Location: Sheffield, UK

Re: zx spectrum in zx81 case

Post by Retrogadgets » Fri May 04, 2018 11:15 pm

20180504_215847.jpg
Ive completely replaced all the ic's except the cpld. I'll try the 14mhz crystal as you said.

McKlaud
Posts: 147
Joined: Tue Dec 19, 2017 10:02 pm
Location: St Albans, UK

Re: zx spectrum in zx81 case

Post by McKlaud » Sat May 05, 2018 12:17 am

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.
Claudius
----------

Retrogadgets
Posts: 9
Joined: Wed Jan 29, 2014 8:29 pm
Location: Sheffield, UK

Re: zx spectrum in zx81 case

Post by Retrogadgets » Sat May 05, 2018 2:30 am

Ordered some Philips 74HCU04's

Post Reply