zx spectrum in zx81 case

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

Re: zx spectrum in zx81 case

Post by Retrogadgets » Fri May 11, 2018 9:41 pm

Zx max 48 still has the weird picture.

Ive completely rewired the lead . The j4 is connected 2-3 and replaced the 74 ic with a philips 74hcu type and still the same.

The rgb signal is it pal or ntsc ? Or does it not work like that.


I dont have the AD chip fitted.

McKlaud
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Location: St Albans, UK

Re: zx spectrum in zx81 case

Post by McKlaud » Fri May 11, 2018 10:12 pm

Do you have an oscilloscope? If so, check 14MHz (74HC004 - pin8) & 3.5MHz (Z80 clock - pin 6) signals on the board and also the Csyns signal on to pin 8 of miniDIN8 socket.

If you touch with a finger the bottom of your board near the 74HCU04 is anything changing on the screen?
Claudius
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1024MAK
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Re: zx spectrum in zx81 case

Post by 1024MAK » Sat May 12, 2018 1:44 am

Retrogadgets wrote:
Fri May 11, 2018 9:41 pm
The rgb signal is it pal or ntsc ? Or does it not work like that.
PAL and NTSC are really just the part of the composite video signal that adds colour to a monochrome video signal. However, lots and lots of people use these 'terms' to mean the video standard that is in use.
Video standards define the number of lines, the horizontal and vertical frequencies etc, etc.

With RGB, the colour information is already present, so there is no 'extra' colour system like PAL or NTSC. But, the number of lines, the horizontal and vertical frequencies etc, has to be correct for the display used. So in the U.K. for example, the RGB signal is an interlaced, 625 line, 15625Hz horizontal, 50Hz vertical frequency system.

Mark

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

Re: zx spectrum in zx81 case

Post by Retrogadgets » Wed May 16, 2018 9:34 am

Got an oscilloscope now. Shall try as detailed above.

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