Why is the Neo 59.18hz?

Which specific component in the hardware is the cause? Is there a way to mod it to be 60hz?

I'm sure you can change one of the crystal oscillators and get closer to 60hz on the horizontal sync. It didn't really matter (and probably why SNK didn't waste resources getting it closer to the exact figure) when the Neo first came out is because it is within the range accepted by CRTs, and LCDs expect something closer to spec, causing the issue with compatibility.

pulstar said:

I'm sure you can change one of the crystal oscillators and get closer to 60hz on the horizontal sync. It didn't really matter (and probably why SNK didn't waste resources getting it closer to the exact figure) when the Neo first came out is because it is within the range accepted by CRTs, and LCDs expect something closer to spec, causing the issue with compatibility.

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Awesome, i'll look into that. I also bought an oddball Laborato Rio bootleg 1-slot to see if it will sync.

Never seen a bootleg motherboard in the flesh, only pics. It'd be interesting to see if it does sync (easier, at least).

ResO said:

Which specific component in the hardware is the cause? Is there a way to mod it to be 60hz?

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This page gives a good overview:
https://wiki.neogeodev.org/index.php?title=Display_timing

The Neo outputs pixels at exactly 6MHz. Each video line has to be a whole number of pixels, and each video frame has to be a whole number of lines (for non-interlaced display). In this case, there's 384 pixel periods per line, and 264 line periods per frame. 6MHz divided by 384 gives a line rate of 15.625 KHz. 15.625KHz divided by 264 gives a frame rate of 59.1856 Hz.

It's not necessary to hit exactly 15734Hz/59.94Hz for a CRT. In fact, a non-interlaced signal will never hit precisely the same timings as a 480i TV signal. So, they get close enough for an arcade monitor, and leave it at that.

You could try slightly overclocking the system.

It would be wonderful if someone knew the magic crystal frequency so everyone could mod their neo's for modern displays.

If heard of overclocked Neo's, how would one go about it?

Maybe upping the 24Mhz crystal oscillator to something like a 26Mhz one, or is it more advanced than that?

I'd love to see a fix for this. My MVS still stutters on my Plasma, with or without a framemeister. Literally every other system works perfectly fine except for the Neo.

Scott said:

I'd love to see a fix for this. My MVS still stutters on my Plasma, with or without a framemeister. Literally every other system works perfectly fine except for the Neo.

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Or just use a CRT.

HeavyMachineGun said:

Or just use a CRT.

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Har har, that's not really the point of this thread. Lots of folks would like to use their neo with modern displays. Just wanted to know the "why" so we know the "how" to go about tackling the issue.

What is wrong with an RGB enhancment mod plus an RGB upscaller?

I never knew there was a compatibility issues with some displays and the MVS. Overclocking the system will likely break some games.

Overclocking the system by replacing the 24MHz oscillator is not going to change any games. As that is the master clock, every other clock is derived from it proportionately and will scale alongside it. No game would know the difference; the parts are not being run against their theoretical limits as is.

To get a refresh rate of 60.00Hz, the 24MHz clock must be replaced by a ((60.00Hz / 59.1856Hz) * 24.00MHz) oscillator, ~ 24.33MHz. Not a common value. The CPU clock, the pixel clock, the YM2610's clock, the audio pitch, the Z80 clock, etc. will now all be increased by about 1%.

If you do that, you're also going to up the horizontal frequency by 1%, getting about 15.7KHz. That's within tolerance, but you might find a display is just as picky about that.

It's all a matter of proportions.