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Hi! About a year ago I did the 60 hz mod on a PAL SMS1. I also replaced the PAL oscillator with a NTSC oscillator.
To complete the conversion from PAL to NTSC i followed the instructions in a youtube video. Sadly the video is no longer availiable and I don’t have the converted SMS1 any longer.

The video instructions was something like lifting pin 6 on the video encoder (CXA1145) chip and connecting it to the clock pin on the Z80 chip.
Then connecting another pin on the video encoder to ground.

Can anyone help me with the instructions to convert a SMS1 from PAL to NTSC other than the 60-hz mod and switching oscillator?

Thanks!

David

This was discussed in another post about a week ago. In theory:

Disconnect the 4.43MHz subcarrier between IC4 and the CXA1145 subcarrier input (pin 6).

Connect the CPU clock from either the Z80 or IC5 to the CXA1145 subcarrier input.

Put both the VDP and the CXA1145 (pin 9) from PAL mode to NTSC mode.

The subcarrier from IC4 goes through a 3.3K resistor and some capacitors before going on to the CXA1145. So this resistor may be a good point to change the subcarrier without cutting traces on the board etc, e.g. remove the 3.3K resistor and insert an inline 3.3K resistor on the pad connected to the CXA1145 only.

Thanks! I saw something similar but thought it was SMS2-specific.

A few more newbie questions if you don't mind.

Quote

Put both the VDP and the CXA1145 (pin 9) from PAL mode to NTSC mode.

Looking at the CXA1145 pinout, pin 7 on the CXA should be connected to 5v to be set to NTSC. I guess I have to lift pin 7 on CXA to prevent shortcircuit?

Which chip is the VDP?

Quote

The subcarrier from IC4 goes through a 3.3K resistor and some capacitors before going on to the CXA1145. So this resistor may be a good point to change the subcarrier without cutting traces on the board etc, e.g. remove the 3.3K resistor and insert an inline 3.3K resistor on the pad connected to the CXA1145 only.

So remove the existing resistor between IC4 and CXA to cut the connection, then add a resistor between CXA pin 6 and Z80 (pin 6 CLK)?

David

Yes, you are correct, pin 7 (not pin 9 as I said above) of the CXA1145P is the NTSC/PAL select. It needs to be disconnected from its ground connection and tied high.

The VDP is IC5.

Yes, removing the resistor cuts the subcarrier connection between IC4 and the CXA.

I replaced the PAL oscillator (53.203Mhz) with an NTSC oscillator (53.693Mhz) and after that the SMS I just doesn't seem to work (black screen, no sound, nothing).

I put the PAL crystal back and everything works fine again. I expected it to be just as easy as converting the Megadrive into a Genesis but I guess its not (only the oscillator change and the switches mod needed).

So I guess more things have to be done except the oscillator and the switches mod to turn my SMS I VA3 into a true NTSC SMS.

Is there a video or tutorial that can guide me step by step to the extra steps needed?

Author	Message
Davideo81 Joined: 21 Aug 2019 Posts: 3 Location: Sweden	Master system model 1, PAL to NTSC conversion Posted: Sun Nov 22, 2020 9:25 pm
Davideo81 Joined: 21 Aug 2019 Posts: 3 Location: Sweden	Hi! About a year ago I did the 60 hz mod on a PAL SMS1. I also replaced the PAL oscillator with a NTSC oscillator. To complete the conversion from PAL to NTSC i followed the instructions in a youtube video. Sadly the video is no longer availiable and I don’t have the converted SMS1 any longer. The video instructions was something like lifting pin 6 on the video encoder (CXA1145) chip and connecting it to the clock pin on the Z80 chip. Then connecting another pin on the video encoder to ground. Can anyone help me with the instructions to convert a SMS1 from PAL to NTSC other than the 60-hz mod and switching oscillator? Thanks! David

asynchronous Joined: 14 Aug 2000 Posts: 741 Location: Adelaide, Australia	Master system model 1, PAL to NTSC conversion Posted: Mon Nov 23, 2020 12:54 pm
	This was discussed in another post about a week ago. In theory: Disconnect the 4.43MHz subcarrier between IC4 and the CXA1145 subcarrier input (pin 6). Connect the CPU clock from either the Z80 or IC5 to the CXA1145 subcarrier input. Put both the VDP and the CXA1145 (pin 9) from PAL mode to NTSC mode. The subcarrier from IC4 goes through a 3.3K resistor and some capacitors before going on to the CXA1145. So this resistor may be a good point to change the subcarrier without cutting traces on the board etc, e.g. remove the 3.3K resistor and insert an inline 3.3K resistor on the pad connected to the CXA1145 only.

Davideo81 Joined: 21 Aug 2019 Posts: 3 Location: Sweden	Posted: Mon Nov 23, 2020 2:10 pm
Davideo81 Joined: 21 Aug 2019 Posts: 3 Location: Sweden	Thanks! I saw something similar but thought it was SMS2-specific. A few more newbie questions if you don't mind. Quote Put both the VDP and the CXA1145 (pin 9) from PAL mode to NTSC mode. Looking at the CXA1145 pinout, pin 7 on the CXA should be connected to 5v to be set to NTSC. I guess I have to lift pin 7 on CXA to prevent shortcircuit? Which chip is the VDP? Quote The subcarrier from IC4 goes through a 3.3K resistor and some capacitors before going on to the CXA1145. So this resistor may be a good point to change the subcarrier without cutting traces on the board etc, e.g. remove the 3.3K resistor and insert an inline 3.3K resistor on the pad connected to the CXA1145 only. So remove the existing resistor between IC4 and CXA to cut the connection, then add a resistor between CXA pin 6 and Z80 (pin 6 CLK)? David

asynchronous Joined: 14 Aug 2000 Posts: 741 Location: Adelaide, Australia	Master system model 1, PAL to NTSC conversion Posted: Tue Nov 24, 2020 11:32 am
	Yes, you are correct, pin 7 (not pin 9 as I said above) of the CXA1145P is the NTSC/PAL select. It needs to be disconnected from its ground connection and tied high. The VDP is IC5. Yes, removing the resistor cuts the subcarrier connection between IC4 and the CXA.

gtsamour Joined: 13 Oct 2011 Posts: 4	Posted: Sat Apr 24, 2021 12:52 pm
gtsamour Joined: 13 Oct 2011 Posts: 4	I replaced the PAL oscillator (53.203Mhz) with an NTSC oscillator (53.693Mhz) and after that the SMS I just doesn't seem to work (black screen, no sound, nothing). I put the PAL crystal back and everything works fine again. I expected it to be just as easy as converting the Megadrive into a Genesis but I guess its not (only the oscillator change and the switches mod needed). So I guess more things have to be done except the oscillator and the switches mod to turn my SMS I VA3 into a true NTSC SMS. Is there a video or tutorial that can guide me step by step to the extra steps needed?

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