Like many consoles of its generation, the Nintendo 64 is zoned. That is to say, each of the 3 usual regions (NTSC / Japan, NTSC / USA, PAL / Europe) had a specific model that could only play same region’s cartridges. In fact, NTSC regions share the same hardware and the protection is only physical (like the Megadrive and Snes) : a simple piece of plastic that could easily be removed. But The PAL model has a different hardware, including a specific region check chip (PIF-NUS) and video encoder to output a (obviously) PAL video signal.

As usual at this time, PAL games were often slower than NTSC ones and had horizontal black bars. Well, actualy on the N64, a few games have less frameskip in PAL (usualy 25FPS) than in NTSC (30 FPS), but 60Hz is still more comfortable on a real CRT.

There are 3 ways to play NTSC games on a PAL N64 :

• Using an Everdrive or any clone : the timing is not perfect because of frequency difference between NTSC and PAL hardware, but it is probably not that noticeable
• Using a NTSC cartrige adapter : same timing “issue” and you also need at least one PAL cartridge
• Convert the PAL motherboard to NTSC : this implies the death of the NTSC board…

I recently purchased a “not working”  NTSC board for cheap, so I decided to try converting my PAL motherboard (DENC-NUS)…

Overview

Here is the components involved in the convertion. There are also two small modifications to do on the back of the motherboard.

Removing components

PIF Microchip

The PIF is a microcontroller that handles several things, including startup and cartridge region check. Using the PIF chip from NTSC console on a PAL one will make the PAL console accepts only NTSC games (JPN and US). The chip is only soldered on surface. The easiest way to remove it, is to use an hotair gun (400°C).

I protected the reset button, because it can easily melt while using the hotair gun.

This is the NTSC PIF-NUS:

And here the PAL PIF(P)-NUS

Crystals

The MX8330 (U7) chip takes a frequency as input and provides a multiplicated frequency output for DRAM (x14 or x17) as well as output for video clock color burst frequency (divided by 4).

On a PAL motherboard, the crystal is 17.72 Mhz. The MX8330 on PAL system is set to multiply this frequency by 14 for DRAM (248 Mhz), and the output for PAL colorburst must be 4.43 Mhz (here, it’s 17.72/4).

On an NTSC moteherboard, the crystal is 14.31818 Mhz. On NTSC consoles, the MX8330 is set to multiply the input by 17 for DRAM (243 Mhz), and the output for NTSC colorburst must be 3.5795 Mhz (here, it’s 14.31818/4)

Without changing this crystal, an NTSC game should probably work like on a standard PAL console with an adapter to launch NTSC games. But as you understood, frequencies for DRAM and colorbusrt output being differents on PAL and NTSC, there would probably be some effects on games that are tightly coupled to timings, like frame drops.

Mounting NTSC components on the PAL Motherboard

PIF Microchip

To prepare the resoldering of the microchip, I added some flux and used a soldering iron to smooth all solder points :

Then, I soldered the PIF by aligning all legs on solder points and passed the soldering iron back and forth (the flux prevent solder joins between legs).

At this point, we have an alien system : NTSC PIF with PAL frequencies and PAL video encoder:

Crystal

Mounting the crystal is pretty easy : the legs are simply soldered on the back of the motherboard.

With the NTSC crystal soldered, we have an even more alien system with bad frequencies for both DRAM and video signals for a PAL motherboard because we did not yet modified MX8330’s settings…

MX8330 hack

As said earlier, the MX8330 (U7) is a clock generator and can multiply the input by 17 or 14. On a PAL system, the pin 7 is bridged to ground, which makes the chip multiply input frequency by 14. With the NTSC crystal installed, the DRAM would run slower than intended (14 x 14.31818 = 200 Mhz instead of 243 Mhz on a standard NTSC motherboard). 

In order to get the good DRAM frequency with the NTSC crystal, the input frequency must be multiplicated by 17, which means that the pin 7 must be bridged to 3v3 instead of ground.

To do so, the pin 7 must be lifted by gently apply a soldering iron on the pin while using a thin blade to lift the pin  

 

Then I added a bit of solder to pin 4 (V-in : 3v3), and I solder a thin wire to bridge pin 7 and pin 4 :

 

Changing the video encoder mode

Video encoders are differents between PAL and NTSC, but ealier versions (CPU-01 and CPU-03 models) provide a PAL/NTSC selector pin to switch the video signal. With the NTSC crystal, the PAL video signal would not be correct and would display a black and white image (NTSC colorburst is 3.57Mhz whereas it is 4.43Mhz for PAL).

The CPU-01 PAL motherboard with a DMENC-NUS video encoder has two jumpers on the bottom to change the video signal : JP2 and JP3.

In order to switch video signal mode from PAL to NTSC, JP3 must be cut and JP2 must be bridged :

Conclusion

My “NUS-CPU (P) 01” motherboard has now an NTSC PIF, crystal and video signal. It plays only NTSC games, thus my Nintendo 64 is now an NTSC version with a PAL reference 🙂

If like me you are using a CRT that does not accept NTSC composite signal, an RGB mod is then mandatory.

Sources

I have been able to do this mod thanks to the all the enthousiast modders that have shared their knowledge.

http://modretro.com/xen/index.php?threads/differences-between-ntsc-and-pal-n64s.14138
https://shmups.system11.org/viewtopic.php?f=6&t=70541
https://bitbuilt.net/forums/index.php?threads/ultimate-n64-ntsc-pal-region-switch-guide.1620
https://n64brew.dev/wiki/PIF-NUS
https://wiki.console5.com/tw/images/e/e3/MX8330.pdf
https://en.wikipedia.org/wiki/Colorburst