How can I convert PAL to NTSC on the MZ-700?

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jejump
Posts: 10
Joined: Tue Jun 04, 2019 9:32 pm

How can I convert PAL to NTSC on the MZ-700?

Post by jejump » Sat Sep 21, 2019 3:21 pm

Hi guys,

I am working on the MZ-700 again that I got from eBay a few months ago. I recently discovered that the video output signal is PAL and the Commodore 1702 monitor I am working with is NTSC. I hope to convert the MZ-700 to be NTSC. There is a jumper that someone on a C64 Commodore forum pointed out to me on the motherboard of the MZ that says PAL. Since it was a closed jumper, I thought maybe I should clip it to make it open and connect my monitor. That didn't work! :( It only made matters worse. Before clipping JP1, I could at least, see the text on the screen. Flipping the RF modulator's BW/Color switch made an even clearer B/W screen. In color mode, it was a slightly fuzzy black screen with white text where the background should normally be blue. I'm pretty sure the MZ-700 is fine because it works (at least, before I clipped the jumper) on my flat panel smart TV. The smart TV is apparently smart enough to determine whether a video source is NTSC or PAL and roll with whichever, but the Commodore 1702 is strictly NTSC.

What more is involved to make the MZ-700 output NTSC? Maybe I should see if there is some kind of NTSC/PAL switch inside the monitor and stick with PAL. :?

jejump
Posts: 10
Joined: Tue Jun 04, 2019 9:32 pm

Re: How can I convert PAL to NTSC on the MZ-700?

Post by jejump » Sat Sep 21, 2019 3:44 pm

I'm also looking at this:

https://www.amazon.com/CIMPLE-CO-Conver ... 384&sr=8-5

For the money, maybe it'll do the job just fine. Hopefully, without much signal loss.

hlide
Posts: 285
Joined: Thu Jan 25, 2018 9:31 pm

Re: How can I convert PAL to NTSC on the MZ-700?

Post by hlide » Sun Sep 22, 2019 2:56 pm

First, you need to change the clock from 17.7... MHZ (PAL) to 14.1... (NTSC) if you want to remove JP1 to switch NTSC. In that case, "The main differences between the overseas versions include changing the video output from NTSC to PAL, changing the CPU clock accordingly (3.58MHz → 3.5469MHz)". The rest should stay as such as i don't think you want a Japanese version (different fonts and monitor).

If you don't do so, frequency will be go from f/5 (17.7/5 ~ 3.5 MHz) to f/4 (17.7/4 ~ 4,4 MHz). The video output won't work properly as well as the NTSC frequency (17.7 instead of 14.1) would be too fast.

S_U_C
Posts: 15
Joined: Sun Feb 17, 2019 6:41 pm

Re: How can I convert PAL to NTSC on the MZ-700?

Post by S_U_C » Sun Sep 22, 2019 4:32 pm

Hi,
as the MZ700 was a Japanese machine NTSC output but they also sold it with PAL output.
If you look at the MZ700 service manual the PAL jumper goes to the LSI chip and it changes the video synch pulses from PAL to NTSC.
On page 6 is the instructions use NTPL choose PAL OR NTSC. I found on the MB as N/PL and it is closed for PAL.
If the quality of the RF module is poor the problem may lie here.
I have seen sevral covert circuits that use 3.58 and 4.43MHz crytals for the timings so the MZ700 is PAL at 3.58MHz (17.7 /5) NTSC at 4.45MHz (17.7 /4)

jejump
Posts: 10
Joined: Tue Jun 04, 2019 9:32 pm

Re: How can I convert PAL to NTSC on the MZ-700?

Post by jejump » Mon Sep 23, 2019 2:11 am

Thanks for all the info. I'm going to give the converter from Amazon a go just because it seems easiest and solder the clipped jumper back together. Maybe I'll be satisfied with that. If not, I'll try to change the clock as you've described.

Is this the main processor's clock too, or just something purposed for the video generator?

hlide
Posts: 285
Joined: Thu Jan 25, 2018 9:31 pm

Re: How can I convert PAL to NTSC on the MZ-700?

Post by hlide » Mon Sep 23, 2019 10:52 am

This is the main clock f where all the other necessary clocks for video and cpu are derived from. PAL CPU clock is f/5 and NTSC CPU clock is f/4 thanks to JP1.

jejump
Posts: 10
Joined: Tue Jun 04, 2019 9:32 pm

Re: How can I convert PAL to NTSC on the MZ-700?

Post by jejump » Mon Sep 23, 2019 11:45 am

Well in that case, to change the clock speed to support NTSC, sounds like I'd be shaving off ~3.6Mhz of CPU processing speed too, right? I suspect that snipping JP1 informs the timers (including video output timer) how to behave so that games play at the right speed, audio is generated at the right frequency, etc., but actual actual Z80 instruction processing speed would be compromised a bit to go this route. Is this correct?

hlide
Posts: 285
Joined: Thu Jan 25, 2018 9:31 pm

Re: How can I convert PAL to NTSC on the MZ-700?

Post by hlide » Mon Sep 23, 2019 8:35 pm

EDIT: I had a hard job to understand what you mean. The CPU and video clock is not really an issue for MZ-700 programs. Very few programs were expecting an exact timing. So yeah, there are some differences but almost all MZ700 programs don't care.

If you want the right NTSC timing you must change the cristal LPHI and switch JP1 open.

One thing, those clocks are very hard to find, I tried with no avail.

hlide
Posts: 285
Joined: Thu Jan 25, 2018 9:31 pm

Re: How can I convert PAL to NTSC on the MZ-700?

Post by hlide » Tue Sep 24, 2019 2:44 pm

More details about NTSC using Φ(14.31818MHz) :

- horizontal timings:
htiming.gif
htiming.gif (3.56 KiB) Viewed 263 times
- vertical timings:
vtiming.gif
vtiming.gif (1.4 KiB) Viewed 263 times
- clock derivations:
clocks.gif
clocks.gif (3.36 KiB) Viewed 263 times

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