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Help fix a NES Clone (Phantom System)
https://forums.nesdev.com/viewtopic.php?f=9&t=15458
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Author:  Fisher [ Thu Feb 02, 2017 3:33 pm ]
Post subject:  Re: Help fix a NES Clone (Phantom System)

That's the problem.
My TVs are automatic, but my kids want to play on their grandparents' home, that has an old PAL-M only TV.
As it is, the console gets a little stronger color on my TV, wich I like.
I don't have a working UM6548 PPU, so maybe trying to build the inexistent circuit might be a solution, but I don't know what the needed parts are nor where they should go.
I never noticed such big difference on the color systems, at last not on the automatic TVs.
But I guess that keeping the console on its original form is a good idea.
I have a (kind of) working Playtronic's transcoder board, but I don't know how it's plugged on the console.

Author:  l_oliveira [ Thu Feb 02, 2017 5:09 pm ]
Post subject:  Re: Help fix a NES Clone (Phantom System)

If I remember well, it has four wires. It takes +5v and gnd. The other two wires take output from the PPU right after the first amp transistor (trace is cut or a resistor is removed, I don't quite remember) and re-inject it at the other side of the interrupted circuit.

Author:  Fisher [ Thu Feb 02, 2017 5:34 pm ]
Post subject:  Re: Help fix a NES Clone (Phantom System)

Nope. It's 7 wires.
And I think at least 2 come from the PPU and one from the clock circuit.
If I had the original wires I could try to guess.
But even this is missing. :cry:
I'll try this path tomorrow, since I had no success trying to find a phase alternating circuit. :-(

You don't have the possibility to take some pictures of the Playtronic's NES interior showing clearly where the wires are connected? All the pictures I could find are not reliable enough to a safe guess.
And I'm really not sure if the board is really working, what makes a guess even more difficult. :oops:

Author:  l_oliveira [ Thu Feb 02, 2017 6:20 pm ]
Post subject:  Re: Help fix a NES Clone (Phantom System)

Fisher wrote:
Nope. It's 7 wires.
And I think at least 2 come from the PPU and one from the clock circuit.
If I had the original wires I could try to guess.
But even this is missing. :cry:
I'll try this path tomorrow, since I had no success trying to find a phase alternating circuit. :-(

You don't have the possibility to take some pictures of the Playtronic's NES interior showing clearly where the wires are connected? All the pictures I could find are not reliable enough to a safe guess.
And I'm really not sure if the board is really working, what makes a guess even more difficult. :oops:


My NES is a USA one. Sorry. I honestly think you could look at "Mercado Livre" for a PAL-M PPU if you really need it to be PAL-M.

Since you already have a working NTSC PPU would be a lot easier to just shove a NTSC crystal in it and call it a day. Have the PPU socketted in case a PAL-M PPU appears for you, you can put it back in it's original state. Of course, that if you can't make the NES transcoder board work for you.

Author:  Fisher [ Fri Feb 03, 2017 2:01 am ]
Post subject:  Re: Help fix a NES Clone (Phantom System)

Well, I found a UA6548 and a LA6548.
I think the UA part is the one I need.
But unfortunately, this will have to wait, since the kids are going back to school and need material, wich usually is a stab!

I'll keep trying... looks like the IC should be a 4069, a CMOS inverter, if I'm right.
The rest of the circuit probably is trying to split the color subcarrier.
I think that's the only part of the signal that needs alternating phase, is it?

Anyway, thanks for the help! :beer:

Author:  l_oliveira [ Fri Feb 03, 2017 6:14 am ]
Post subject:  Re: Help fix a NES Clone (Phantom System)

UA6548, right! I said UM but it's UA.

Author:  Fisher [ Fri Feb 03, 2017 6:54 am ]
Post subject:  Re: Help fix a NES Clone (Phantom System)

I think I have seem UM and UA, even PM02 and PM03.
Maybe they're from different manufaturer or batch.

Author:  l_oliveira [ Fri Feb 03, 2017 7:54 am ]
Post subject:  Re: Help fix a NES Clone (Phantom System)

Different manufacturer. But I think only UMC (UA6548) makes PAL-M PPU.

Author:  Fisher [ Fri Feb 03, 2017 3:56 pm ]
Post subject:  Re: Help fix a NES Clone (Phantom System)

I asked a guy who's selling a schematics.
He said it's a 74LS74.
Any guesses?

Author:  lidnariq [ Fri Feb 03, 2017 7:56 pm ]
Post subject:  Re: Help fix a NES Clone (Phantom System)

I think I'm surprised at being able to do the entirety of the encoding transformation in discrete components, but if you could, it would make sense that a 74'74 would be used to keep track of whether the PAL phase should be 'clockwise' or 'counterclockwise'.

(I suppose that's the point of Brazil's PAL-M ? Because you "just" need to modify the chrominance on every other scanline, and change the angle of the colorbursts?)

And, certainly, looking at the PCB, I can see what a 74'74 would be doing in socket CI-10: Pins 8-13 make a monostable multivibrator (starts on a rising edge of pin 11; on time a function a of R53 and C20), while pins 1-6 are just a divide-by-two (clocked on rising edge ultimately from pin 11)

Author:  Fisher [ Sat Feb 04, 2017 6:28 am ]
Post subject:  Re: Help fix a NES Clone (Phantom System)

The technical excuse was that the alternating phase would make a better color, less suceptible to interferences, wich I'm not really sure is true.
But I think, like most things done here, it was sort of a political decision.
With this, the national industry would be "protected" from the "evil" import products.
But it was kind of a shoot on the foot, since the national industry couldn't export the product as-is and a market expansion was not very viable.
Imports also would not be easy, since the equipment would need to be modified and not many people had the knowledge back in the day.
I may be wrong though...

These are part of my doubts I was willing to ask in other thread. So, here I go with the other part:
- I need to take a picture of a SNES that got a transcodification problem and try to understand it. It consists of two resistors and a capacitor on the video encoder. I need to write down the values.
- On the MegaDrive's case I think that it's the alternating phase that's the problem. It gets black and white and with alternating colors. But it only happens in some games, that's weird!!
- I need to take a look at the PS1's transcodification circuit. If I remember correctly it was a transistor, a crystal and two resistors.
Maybe that was a little oscilator that generated the color subcarrier frequency.
- How's the N64 transcodification done? I think it's similar to SNES.
- And at last but not least, is the color subcarrier what carries the colorburst? I'm a bit confused about these two names...

Author:  Joe [ Sat Feb 04, 2017 8:02 am ]
Post subject:  Re: Help fix a NES Clone (Phantom System)

Fisher wrote:
- How's the N64 transcodification done? I think it's similar to SNES.

The Brazil-specific N64 (NUSM-001) natively generates PAL-M video, it doesn't transcode.

I assume the 14.3 MHz oscillator in this N64 is 14.302 MHz instead of 14.318 MHz, but I don't know how to tell for sure. (Also, it has an undumped boot ROM... we should get someone on that.)

Author:  Fisher [ Sat Feb 04, 2017 10:09 am ]
Post subject:  Re: Help fix a NES Clone (Phantom System)

How can this ROM be dumped.
I think I have a brazilian one, but it's not booting.

Author:  l_oliveira [ Sat Feb 04, 2017 11:44 am ]
Post subject:  Re: Help fix a NES Clone (Phantom System)

Joe wrote:
Fisher wrote:
- How's the N64 transcodification done? I think it's similar to SNES.

The Brazil-specific N64 (NUSM-001) natively generates PAL-M video, it doesn't transcode.

I assume the 14.3 MHz oscillator in this N64 is 14.302 MHz instead of 14.318 MHz, but I don't know how to tell for sure. (Also, it has an undumped boot ROM... we should get someone on that.)


The main "transcodification" thing on the Brazilian N64 is a pin of the video encoder IC which has it's connection inverted (from + to GND or GND to + I don't remember) and the RCP-NUS clock source is replaced from 14.31818 to 14.30444. The PIF-NUS-M is important to give the video the correct timing when interlaced video is used. If you mod a NTSC unit to PAL-M and keep the NTSC PIF you will have B&W video on interlaced video due to a timing problem with the chroma burst. (A good example is the N64 Killer Instinct game)

Author:  l_oliveira [ Sat Feb 04, 2017 11:59 am ]
Post subject:  Re: Help fix a NES Clone (Phantom System)

Fisher wrote:
- I need to take a picture of a SNES that got a transcodification problem and try to understand it. It consists of two resistors and a capacitor on the video encoder. I need to write down the values.


I used to use 3K3 and 104 (100nf) capacitors. What that circuit does is inject the CSYNC on the PAL/NTSC selection pin of the video encoder so it switches the mode during the blanking phase. That hack makes it generate PAL video signal while using NTSC timing. Same trick Tec Toy used with the MC1377 on the first Master System console.
Fisher wrote:
- On the MegaDrive's case I think that it's the alternating phase that's the problem. It gets black and white and with alternating colors. But it only happens in some games, that's weird!!

Again, timing problems with the color burst. They put two 100nf capacitors at strategic spots to reduce that a bit.

Fisher wrote:
- I need to take a look at the PS1's transcodification circuit. If I remember correctly it was a transistor, a crystal and two resistors.
Maybe that was a little oscilator that generated the color subcarrier frequency.


PS1 has some special optimizations to make the CXA145 image better:
The "GPU" (frame buffer is a better denomination here) outputs a triangular wave for color carrier which helps reducing edges. It also generate that in phase with the HSYNC which helps with dot crawl. Gives out a crisp image on NTSC. Transcodification on that system throw the optimizations out of whack and you get worse picture quality as result. It also has optimizations for PAL video but those are active if the vertical frequency is 50Hz.

Fisher wrote:
- How's the N64 transcodification done? I think it's similar to SNES.

Replied already on another post.

Fisher wrote:
- And at last but not least, is the color subcarrier what carries the colorburst? I'm a bit confused about these two names...

Colorburst is encoded on the sync signal during the blanking phase.

Basically... PAL-M is a hack and you're better avoiding it like the plague.

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