65XE PAL to NTSC mod

"Small" Atari computers
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65XE PAL to NTSC mod

Post by PanzerGeneral »

I wanted live NTSC hardware for various tests. Since I couldn't buy an Atari or NTSC version, and I managed to get Antic and GTIA in NTSC version I decided to convert PAL to NTSC.
The 65XE board without ECI (i.e. revision CO70025) was placed under the soldering iron.

The remake is fairly straightforward, and the description in reverse order can also be applied to the rework in the opposite direction, so it might be useful to someone.

1. Desolder the Antic and GTIA systems, solder the sockets instead.
At this stage, the replacement of the Antic and GTIA systems alone allows you to determine whether the systems are operational, because in general, apart from the comments below, the computer is working normally.
a) Replacing Antic with the NTSC version only changes the aspect ratio, the colors remain the same as in the PAL version.
b) Replacing the GTIA with the NTSC version causes the colors to disappear and the image becomes black and white, because we still have a PAL clock on the disc.

2. Replace the quartz on 14.187576 with 14.31818

3. We throw out the PAL clock from colors.
In order to finally make the record NTSC exactly as it was produced in the factory, the following components must be discarded:
- quartz 4.433618
- 74LS74 integrated circuit
- resistors R69, R70, R71, R72, R73
- capacitors C58, C59, C60, C61, C111
- L8 coil

Simplified version: if we want to do the operation faster, and at the same time be able to do a quick return to PAL, it is enough:
- remove resistors R70, R72
- desolder Q6 transistor from the board
These treatments cut the PAL clock output from the GTIA and basically do the trick.

4. Solder the jumper in place of W2 (or the 0R resistor as it was in the original NTSC)

5. Regulation.
We'll have weird colors after reworking. In my case, everything was mostly pink and blue.
To set the right colors, we turn the potentiometer on the motherboard. At the same time note: in the case of PAL we are used to the fact that the colors change only a little, but with NTSC you can spin here by completely changing the palette.
It's best to run "Atari control picture". We shoot until we get the effect that the colors from the line "2" are the same as the colors from the line "F" and that they are shades of, say, brown and gold. Edit: then we shoot a bit further, to push the brown with "F" out of the palette.
It is not important what exactly these colors are, because they are a bit different on every Atari, but it is important where the "2" and "F" are repeated. If you set it like this, all games will look roughly correct.
How to repeat this color you can see by running the "Atari control picture" program in the Altirra emulator and switching the system to NTSC.

And that's it, we have an NTSC board that works as it should.
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65XE PAL to NTSC mod

Post by Valdor »

Great idea! Thanks for the description, because somehow the purchase of the NTSC version goes like blood from the nose and maybe it will end up with a rework (maybe I won't even break my computer:
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65XE PAL to NTSC mod

Post by Hover »

Well, neither do I, and I have never seen NTSC with my eyes...
But after what you wrote, I can see that I made a mistake.
In PAL, the color $ 1x and $ Fx seem to be repeated, while in NTSC the color $ 2x is the color equivalent to $ 1x from PAL.
So if I set in NTSC that the color $ Fx is like $ 2x, then I should turn the potentiometer a little more so that this color with $ Fx "pushes off the scale". Turning the knob moves the colors "up" and at the same time extends the range.
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65XE PAL to NTSC mod

Post by Yavin »

Exactly. Even though Never The Same Color, the scale is bigger than in PAL :)
Maybe the compo graphics should be made in NTSC after all? <rotfl>
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65XE PAL to NTSC mod

Post by alvin »

Their joke "Never The Same Color" may come from the fact that in the Atari NTSC, when we turn this potentiometer, the colors change very much when the potentiometer is turned slightly. While in PAL I am used to the fact that, after all, the colors are similar and they only change a little, or at all they only turn on and off, so in NTSC, by turning you can change the entire palette into a very seriously large scope. A slight twitch of the potentiometer is enough and we have a completely different palette. I can't imagine that it would be possible to set up all the NTSC Atarks in the factory in the same way. It would be easier in PAL, and even if it is not perfect, you still have, for example, blue, only one pale, one juicy, one darker, one lighter, one is greenish more, and the other less. But at NTSC, that's a completely different story. If you set green to green, blue turns pink - but not that it is slightly pink, you have pink instead of blue. If you set the blue one reasonably well, yellow turns into pink in turn. Go to the forest, some madness :-)
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65XE PAL to NTSC mod

Post by Zenobi »

The wonderful world of Walt Disney :) And it would not be possible to construct a simple resistor-transistor system so that the rate of change was more linear and that the palette could be set more precisely? Do you have any idea, isn't it so trivial?
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65XE PAL to NTSC mod

Post by Computeoguy »

Such precision can be achieved, for example, with a multi-turn potentiometer. They are such that you spin a few turns and you have such a long scale for these few turns. For example, something like that.
Or otherwise: there is a 500k potentiometer in the Atari, you can check what is the useful range for a specific Atari copy and then give, for example, a 100k potentiometer, and solder resistors on the sides so that the whole has a total of 500k, but the adjustment took place in these 100k just.
Perhaps it would be enough to really replace the old potentiometers with some new decent ones, because what is, after many years it works poorly and does pranks :-)
I't does not compute....
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65XE PAL to NTSC mod

Post by ThatGuy02 »

Okay, it turned out that the potentiometer I had on the board has enough, so I replaced it with this one:
After replacing the potentiometer, the adjustment range is quite large and a lot changes with a small movement, but the precision is sufficient for you to adjust these colors exactly with such a range and that nothing escapes. So I think that it is enough to use a new decent potentiometer and everything is fine. Now I have the colors adjusted correctly and they are stable, nothing changes in the colors by itself :-)
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