Converting a PAL Turbografx to NTSC

[low_budget]

I recently acquired a new in box PAL Turbografx, knowing it's basically a crippled version of the Turbografx 16 / PC Engine family.

The PAL version runs at a slower clock speed, so games run noticably slower and the sound pitch is off. The composite video output incompatible with probably 95% of the TVs in the world (possible exaggeration.) Even if the system is RGB modded, there's still black bars at the top and bottom of the image.

My goal is to fix all that.

Here's some interesting things I've found about the PAL Turbografx so far:

• Despite fitting in essentially the same case as the U.S. Turbografx, the PAL board is a complete redesign with many surface mount components on the solder side of the board.
  
  Since the PC Engine chipset was designed only for NTSC, many extra components were necessary, such as a CXA1145P video encoder to produce PAL compatible 50Hz video.
  
  The CPU is marked HuC6280A and the video chip is HuC6260A. The "A" suffix not present in the NTSC systems. I have no idea if there's any differences between them.
  
  Many of the video output pins of the HuC6260 are not connected, which sucks for what I'm trying to do here. There's R, G, B, but no sync or luma.
  
  Instead of the U.S. version's 21.47727 MHz oscillator generating the clock signal, the PAL system has two separate clock circuits providing 21.32825 MHz and 17.73448 MHz. This makes the PAL Turbografx clock the CPU 0.04965 MHz slower than the NTSC system's 7.15909MHz speed (which all released games were designed to run at.)
  
  The system has what appears to be a custom ASIC, "PCZ80". This chip accepts the 2 clock frequencies and distributes them to the CPU, GPU, and CXA1145P. It also modifies the GPU's sync signal that's fed to the CXA1145p.
  
  Worse yet, the stupid "PCZ80" IC screws with the GPU clock signal. After looking at it on my oscilloscope, it seems to introduce interrupts which slow down the graphics further!

I suppose all this was necessary to make it PAL compatible, but no PAL region games were ever released. Not even the Blazing Lasers ROM for the pack-in was changed for the PAL console.

I have tried some things so far:

• First thing I did to my test system was remove the CXA1145P and PCZ80 ICs and replace them with sockets. I also replaced the 7805 regulator with a switching regulator so I wouldn't need the heatsink attached during testing.
  
  First experiment involved converting the CXA1145P into NTSC mode. Using the data sheet, I added on a clock circuit to generate the 3.57MHz color subcarrier and jumpered the NTSC / PAL selector pin to 5v.
  There was video on my CRT, but it looked like ass. It had black bars top and bottom and was fairly blurry, but there was color. I connected it to the LCD TV and it was all jacked up. No color, weird pixillation of solid areas, bad signal.
  
  Second experiment involved changing the original system's 21.32825 MHz crystal with a 21.47727MHz one. This gave the CPU the clock speed it was designed for and fixed the sound issue. Still had slowdown in the graphics though.
  
  Third experiment involved removing the GPU's clock signal provided by that cursed PCZ80 chip, and tapping it off the CPU's clock. This completely screwed up the sync of the image. I think I am getting closer though.
  Fix one problem, find another. Fix that problem find another, etc. Eventually you fix all the problems.
  
  Fourth experiment results to follow.
  I'm working on some PCBs to help with the mod and testing. The key here will be undoing everything that wretched PCZ80 chip does.

As part of the project, I designed an update to my RGB to composite & s-video converter, v1.2. It's very small and uses the BH7236AF. It also has pins to work with Viletim's component video add-on designed for the NESRGB.
I hope to get some good full screen RGB video out of the PAL Turbografx that I can feed into this converter and get some nice RGB, s-video, and composite video. This will also work with many different game systems and vintage computers as well.

[YANDMAN]

there is a company in france that does complete modification including everything you are hoping to do, maybe look them up.

[muckyfingers]

Here is all the info you need and make sure to change your CXA1145P to NTSC mode, (which you have). I've done the mods and it does work.

http://dreamjam.co.uk/emuviews/old2011.php

PAL timing and NTSC modification
There isn't much information about the PCZ80, though sources seem to indicate it is a Z80-based microcontroller. However it generates complex high-frequency signals, so either it has a very capable timer peripheral or it isn't a MCU at all, and is some kind of small-scale gate array. Relevant pins are:

Pin 2 - Reset input.
Pin 4 - Unused (active-high horizontal sync output)
Pin 5 - Unused (active-low horizontal sync output)
Pin 6 - 21.32825 MHz clock input (X201 via 74HCU04)
Pin 10 - 17.73448 MHz clock input (X202 via 74HCU04)
Pin 11 - 4.48 MHz clock output to CXA1145 "XO IN" (X202/4)
Pin 15 - 21/17 MHz clock output to HuC6260A
Pin 16 - Composite sync output to CXA1145 "C-SYNC IN"
Pin 17 - Vertical sync input from HuC6270
Pin 22 - 21.32825 MHz clock output to HuC6280A
While not fully implemented, to modify a PAL system to NTSC make the following changes:

Replace X201 with a 21.477270 MHz crystal.
Replace X202 with a 3.579545 MHz crystal.
Remove IC115 and socket it.
Jumper IC115 socket pin 6 to pins 15 and 22.
Jumper IC115 socket pin 10 to pin 11.
Cut and lift pin 7 of IC117, tie to +5V.
This clocks the Hudson chipset at NTSC speeds, and provides a 3.58 MHz color subcarrier for the CXA1145 as well as putting it in NTSC mode. What's untested is recreating composite sync for the CXA1145. I think you can do it by XORing the V-Sync and inverted H-Sync outputs of the VCE together, but the real VCE composite sync leads/lags from these two sync outputs. So the picture may not be centered and the equalization pulses will be missing; though in practice most modren monitors don't need them. While the VCE provides a composite sync output on the luma (Y) pin, it isn't clear if a LM1881 sync splitter could be used without the rest of the composite video circuit being implemented, which is otherwise missing on this system. And lifting the VCE pins to make the necessary connections could be quite difficult.

[mickcris]

thesteve posted how to convert it over at the pcenginefx forums recently. Its fairly easy to do. I did it to one and it works fine.

http://www.pcenginefx.com/forums/index. ... ic=18926.0

You need to register to view the thread though. its basically the same as above but has pictures. here is a pic of my board;
http://i.imgur.com/GdjSoMJ.jpg

i also cut the traces and rerouted the pins on the din so I could use a normal DIN8 jack with the same pinout as the PCEngine/TurboDUo:
http://i.imgur.com/kshs9hl.jpg

[low_budget]

Thanks for the links and mod pics.
I didn't know somebody already had a workable solution.

I haven't registered, so I couldn't read the whole post. From your picture, it looks like the sync is pulled off the luma pin. I see the original clock circuits are used with different crystals.

The modification I had in mind will work a little differently.
Hopefully, I can combine the horizontal and vertical sync signals into a usable composite sync. This will eliminate the need to solder to the fragile HuC6260 graphics chip pins.
I'm also going to try a modified version of the Super 8 bit's 21.47727 MHz clock circuit to replace the on-board clocks entirely.

I designed some PCBs I'll be testing soon that will plug into the CXA1145P and PCZ80 sockets.


I'll post my results. If I don't reply anymore, that probably means it didn't work, LOL.

[RGB32E]

Since it has a CXA1145 you should be able to tap CSYNC from pin 11 (CSYNC out) and add a series 75 ohm resistor and 220uF capacitor just like the RGB out pins.

What I'm curious to know is what is the circuit between the Hu6260 RGB pins and the CXA1145 RGB input pins?

[low_budget]

Tapping the sync of the CXA1145 would still have the top/bottom black bars. This is because the sync fed to the CXA1145 has already passed through the PCZ80.

The biggest challenge it seems will be getting the correct sync without having to solder to the fragile graphics chip pins.
This is one of my goals, as I may make this into a kit for sale and I don't want much risk of people damaging their systems.

I hope to have an update next week when I get my boards.

[thesteve]

the Csync pin is such a low output the CXA didnt like it, but was happy with the 5V luma signal which has around 1V of sync
as for the fragile pins, its not an issue as they dont need to be lifted off the board

[RGB32E]

So, you aren't able to tell us where the RGB lines are routed and what components exist (if any) between the Hu6260 and CXA1145P for the RGB lines?

[thesteve]

the RGB pins should be direct to the CXA (capacitor coupled?) (didnt have to touch them)
i believe the ex bus pins are all present as well

only real change to the circuit was eliminating the MCU that was providing the sync info
the CPU clock was changed for the correct frame rate and the CPU and PPU clocks tied together
the clock that was running the MCU got re-purposed to run the color burst directly
Vsync out from the 6260 had to connect to Vsync in on the 6270

before the mod the CPU was run at a slightly lower speed
the 6270 was run at the normal speed and paused at the end of each frame to wait for Vsync from the MCU
Vsync from the 6260 was ignored

[low_budget]

The RGB lines from the HuC6260 go direct to the expansion port pins and capacitor coupled to the CXA1145 input pins, yes.


It seems the PCB I made for the NTSC to PAL adapter isn't quite right yet. I need to tweak the circuit and add some additional components. So, testing this may take a while. Haven't had much time lately.

I did get my composite / s-video / RGB encoder mounted pretty nicely using a PCB that plugs into a socket formerly occupied by the CXA1145. Won't be able to test it until I can get the sync signal just right though.




I also designed an easy install RGB mod board for the Turbografx 16. It solders directly to the expansion port pins, flat against the Turbografx PCB. There isn't much room here, but the board fits even with the RF shield on. I had to use tantalum capacitors since aluminum caps wouldn't fit, as well as a .032" thick PCB.
It's nothing special circuit-wise. There's a THS7314 amplifier for RGB as well as a LM1881 sync separator IC circuit for sync.

It will work with any member of the Turbografx / PC Engine family.

All systems without the expansion port like TurboDuo and TurboExpress will need four 30ga kynar wires to the Hu6260, as well as power and ground connected.

So far, the easy installation option for the RGB amp is only tested working on the Turbografx 16.

I have a Japanese Supergrafx which has the expansion port, but the RGB mod board won't fit in the space provided without modifications.

I hope other systems will be compatible with the easy installation of the RGB board, but I can't buy them all to test, LOL.

The picture quality using the RGB amp on a Turbografx 16 with my XRGB mini was quite good. No jailbars or interference whatsoever.
Eventually, I'll test some other RGB converters.


I don't have any photo hosting account, but I have pictures available here: http://atariage.com/forums/topic/239112 ... x-to-ntsc/

[low_budget]

Here's my new Turbografx 16 easy install RGB mod, the TGezRGB.
It works quite well and is the cleanest RGB install I've seen.



They're available from my website for $39
http://www.lowbudgetify.com

I have not abandoned the PAL Turbografx conversion to NTSC.
It's just taking a little longer than I thought.

Updates when available.

[kamiboy]

Is that two three channel amps I see on that board? Does that mean it amplifies the sync in addition to the RGB channels?

Visiting your website I am a bit confused. Now obviously the Duo models lack the expansion port so the mod is slightly more messy on them, but what about the old PC Engines which have the expansion port.

Are their port pinout on the board side identical to the one in the TG16 so this PCB can just be mounted on top like it is supposed to?

[low_budget]

The TGezRGB board can only be soldered directly on the expansion port pins if installed in the Turbografx 16.

Technically, it can be soldered to a PC Engine expansion port, but then it would not fit in the case. I don't know if I'll make a board designed for the PC Engine or other systems.

Non Turbografx 16 systems need the board mounted elsewhere and 6 additional wire connections to points on the motherboard.

The circuit uses a THS7314 for RGB amplification, while a LM1881 brings the weak sync signal from the HuC6260 up to the correct level.

[low_budget]

I haven't worked on the original PAL Turbografx to NTSC conversion kit in a while.

Are there many PAL Turbografx owners out there that would want to convert to NTSC using a set of two add-on boards?

I know the PAL Turbografx is quite rare, but most of the systems out there are in very good condition or new old stock. A new PAL Turbografx is around $200 while a North American system new is around $900 or more.

I have done a lot of work so far on this, and gotten some good advice from someone how to fix some of the issues I've been having.

The goal would get the system running at correct clock speeds and give correct NTSC video and RGB in full screen.
It would offer RGB, s-video, and composite video options. Component video may even be possible with an extra add-on board.


I'm just trying to do an interest check here to see if I should focus on other things.