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PostPosted: Sat May 06, 2017 2:30 pm 
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You will need a NTSC PPU too, or else you'll get color only on some TVs, if any.


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PostPosted: Sat May 06, 2017 3:27 pm 
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You need a NTSC crystal and a NTSC PPU IC.


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PostPosted: Sat May 06, 2017 7:08 pm 
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Maybe the transcoding circuit built arount the 74LS74 could be modified to create a correct NTSC color subcarrier from a PAL-M PPU IC?
But the easier way definetelly is to change the PPU.
Can someone suggest a good place to get one NTSC PPU?
I couldn't find one, be it original or clone (the only NTSC clone I know is the UA6528), at least here in Brazil.

I really need to revisit this and the MegaDrive stuff, doing some tests with them.
An interesting fact on the MegaDrive's circuit is that the rainbow banding practically disappears if I use a crystal to generate the Color Subcarrier frequency.
It's becomes very visible if I connect the VDP's output to the encoder.
I really need to draw these schematics and get some pictures...
It will certanly help to show what I mean clearer.


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PostPosted: Sat May 06, 2017 8:47 pm 
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You're transforming the banding into dot crawl by using a crystal for color carrier frequency. The banding is fixed because it's generated by the same clock as the video (the color carrier coming from the VDP is synchronous to the horizontal sync). By switching to a free-running oscillator you have the interference drift around the screen, usually from left to right (may vary depending on the adjustment of the circuit, if there's any or the ambient temperature).

The NES has some measures on the PPU to diminish the effect of the banding/dot crawl artifacts. SEGA stuff not.


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PostPosted: Sat May 06, 2017 11:20 pm 
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Guys, thanks for the quick answers.

Luckily I have spare PPU(RP2C02G-0) here. Hopefully it is working.
I am planning to install the hidef nes mod in the Phantom. I already have the console and the mod kit. Just waiting for the desoldering gun to arrive so I can start the project.
Should I create a new thread or just post here?

Gonna need your help!!!


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PostPosted: Sat May 06, 2017 11:22 pm 
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Fisher wrote:
Can someone suggest a good place to get one NTSC PPU?


I have two NTSC PPU's here but since they are not tested I can't be sure both are working. In case they are I will have one for you.


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PostPosted: Sun May 07, 2017 7:59 am 
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l_oliveira wrote:
You're transforming the banding into dot crawl by using a crystal for color carrier frequency.

I think you're right, here are some pictures:
With Crystal:
Attachment:
File comment: Carrier with crystal
my_photo-1.jpg
my_photo-1.jpg [ 155.59 KiB | Viewed 479 times ]

With the VDP:
Attachment:
File comment: Carrier with VDP
my_photo-4.jpg
my_photo-4.jpg [ 141.83 KiB | Viewed 479 times ]

Would an S-Video mod eliminate the dot crawl?

The MegaDrive I'm using is a clone, it has jumpers to set many features, but unfortunately it hasn't an US/JP jumper.
I added a switch to do that, but looking at it today I see I totally goofed up back in the day :oops: .
It was being used without a top cover, wich I only could get several months later.
This is the MegaDrive in question:
Attachment:
File comment: MegaDrive Clone
20170507_102938.jpg
20170507_102938.jpg [ 860.37 KiB | Viewed 479 times ]

I found a switchless mod sometime ago and I'm willin to build it.
Any idea if it works fine?
melovictor wrote:
Should I create a new thread or just post here?

I think it's up to you to decide what is better, both options are fine, I think.
Anyway I really wish to see how this mod will be made.
So please, post as many pictures and videos as possible.
melovictor wrote:
In case they are I will have one for you.

Having an original CPU/PPU set would certanly help in this project I started a while ago but it is just stuck right now :cry: .
But I'm worried about the costs, specially the shipping.


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PostPosted: Sun May 07, 2017 9:12 am 
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Fisher wrote:
Would an S-Video mod eliminate the dot crawl?


No, but it will reduce the banding considerably if you return to using the VDP clock. The dot crawl is still noticeable even on S-Video, particularly because it has motion, while the banding is static.

The motion can be distracting for some people. That is the main reason why it's preferable to keep the banding than "upgrade" to dot. crawl...

To get rid of dot crawl AES NEO-GEO have a complex circuitry with a PLL feeding back clock fluctuations from the 3.57Mhz oscillator at the CXA1145 IC into the 24MHz oscillator which clocks the system. Any fluctuations on the color carrier frequency are compensated on the main VDC (Video Display Controller) making sure the clock which generates the horizontal sync keeps in phase with the chroma carrier.

Playstation (the first one) in addition to keep it's chroma carrier in phase with the horizontal, feeds a triangular wave to it's CXA1645 instead of a square wave, further reducing image artifacts on spots where colors change abruptly.


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PostPosted: Sun May 07, 2017 12:27 pm 
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HiDef board in place...
Attachment:
IMG-20170507-WA0115.jpg
IMG-20170507-WA0115.jpg [ 162.7 KiB | Viewed 455 times ]

HDMI connector
Attachment:
IMG-20170507-WA0109.jpg
IMG-20170507-WA0109.jpg [ 202.3 KiB | Viewed 455 times ]


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PostPosted: Mon May 08, 2017 5:12 am 
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Cool!!
Looks promising!!


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