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Mission: Convert PAL Turbografx to NTSC


low_budget
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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. 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.

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.

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Edited by low_budget
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Fascinating read. But aren't PAL Turbos even more rare than the NTSC models? Since all PAL games are identical ROMs to NTSC, it may be cheaper to just import.

 

But I guess this is one of those "because I can" mods. I've read up on some of your other projects. Keep it up and keep us posted! :thumbsup:

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posted this on your thread over at shumps, but will put it here also:

 

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.
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
And PAL turbografx systems may be more rare, as in not as many made, but they are pretty much useless as they run slower. You can get brand new ones still from a few different places cause no one wanted them. There are no sources with large numbers of new NTSC Turbografx systems still available.
Edited by mickcris
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Thanks for the links and mod pics.

 

Looks like some nice work.

 

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 for sync.

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 updates if it all works!

Edited by low_budget
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  • 3 weeks later...

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 RGB to composite / s-video 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.

 

This board will also work for any PC Engine or Turbografx system if the R, G, B, sync, power, and ground inputs are wired to the correct points.

 

I might offer these for sale if there's enough interest.

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the rgb board looks nice. it looks like it might be too big for the pc engine, have you tried to fit it in one? since the port is upside down on the tg16, the board would need to be on the other side of the pins on the pc engine.

http://www.mmmonkey.co.uk/pc-engine-rgb-mod/

 

eidt:

nevermind, i think you meant that to use it you would have to run wires to the points on the board.

Edited by mickcris
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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.

 

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.

 

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 with my XRGB mini was quite good. No jailbars or interference whatsoever.

Eventually, I'll test some other converters.

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If I understand correctly, the EXP ports are the same between US and Jap, but the US uses a trapezoid harness, and the Jap used a rectangle. So if the RGB board used the bare connector and not a molded socket, it should fit either model, correct?

 

They should have created a pass through for the data pins in the CD-ROM units. As is RGB only works with bare system + Hucards.

Edited by stardust4ever
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its the same, but since the tg16 board sits upside down in its case and the pc eninge boards all sit upright, the pins you solder to are on the opposite side. see this:

http://www.mmmonkey.co.uk/wordpress/wp-content/uploads/2012/09/PCE-RGB-pinout-bus.jpg

so i think the board would have to be slimmer to work, or a new board would need to be made for the pc engine.

 

also rgb does pass though the port. I have modded a couple PCE briefcase units, Ten No Koe 2's, etc..

Edited by mickcris
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the link works when i click on it. its just a picture of the pc engine port to show that the RGB pins are on the opposite side. Its a picture from the guide i had linked to a few posts above

 

and the ports are the same pinout on the outside when the consoles are back together.

Edited by mickcris
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On the PAL to NTSC conversion:

 

I haven't had any luck getting the sync combiner circuit to output a usable sync signal.

I think I'm going to abandon this approach.

 

It looks like pulling luma off the HuC6260 is going to be the way to go (for sync.)

Instead of a direct connection, I'm going to try running it through a LM1881 sync stripper circuit.

Probably wont be much progress on this for a while.

 

 

On the Turbografx 16 easy install RGB board:

 

It's looking like the NTSC version Turbografx 16 is the only system that can solder directly to the expansion port pins.

It does fit on the PAL version, but I haven't tested it and it might not handle the sync correctly.

 

So I'll look into making RGB amp boards for some PC engine versions.

 

If anyone knows a good PC engine model that would be ideal for something like this let me know.

I already know the Supergrafx isn't a good candidate.

 

The system would need a flat area about 3/4" x 1-3/4" by the RGB pins and 0.150" height clearance.

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@lowbudget Awesome you are attempting this. I just pull from the EXP port but I understand the need to tap on the PCB side if you're running a CD-ROM or other unit. Keep us updated, thanks.

 

 

the link works when i click on it.

Forgive me for the threadcrap, but

 

NOT FOUND

You tried going to http://www.mmmonkey.co.uk/wordpress/wp-content/uploads/2012/09/PCE-RGB-pinout-bus.jpg, and it doesn't exist. All is not lost! You can search for what you're looking for.
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  • 3 weeks later...
  • 3 weeks later...

Surprisingly, I have not stopped working on making the PAL Turbografx to NTSC project.

 

 

So I ended up making a new PCB to replace "IC115" that does two things.

 

Generates 21.47727MHz clock signal for CPU and the graphics chips.

 

Has a LM1881 IC to convert luma from Hu6260 pin 40 to raw sync.

 

 

It will require IC115 be desoldered and a precision socket installed in its place. Then the board plugs in, and a pad is soldered to pin 40 of the HuC6260 with 30 ga. kynar wire.

 

 

Installation can be done two ways:

 

I removed the CXA1145 and replaced it with a precision socket. I replaced the on-board video circuitry with a BH7236AF video encoder.

This provides RGB, s-video, and composite video.

This method doesn't require changing either crystal on-board.

 

A simpler way is to replace the 17.73448MHz crystal with a 3.579545MHz one, then lift pin 7 of the CXA1145 and connect to +5v. This only offers composite output.

 

 

 

I recently got a PC Engine and found the TGezRGB was not even close to fitting using the direct solder method. (see picture)

 

So now I'm working on a redesign specifically for the original model PC Engine.

 

Even though I'm going to use the same circuit, it will still require a complete redesign of the board.

 

 

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Edited by low_budget
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Surprisingly, I have not stopped working on making the PAL Turbografx to NTSC project.

 

 

So I ended up making a new PCB to replace "IC115" that does two things.

 

Generates 21.47727MHz clock signal for CPU and the graphics chips.

 

Has a LM1881 IC to convert luma from Hu6260 pin 40 to raw sync.

 

 

It will require IC115 be desoldered and a precision socket installed in its place. Then the board plugs in, and a pad is soldered to pin 40 of the HuC6260 with 30 ga. kynar wire.

 

 

Installation can be done two ways:

 

I removed the CXA1145 and replaced it with a precision socket. I replaced the on-board video circuitry with a BH7236AF video encoder.

This provides RGB, s-video, and composite video.

This method doesn't require changing either crystal on-board.

 

A simpler way is to replace the 17.73448MHz crystal with a 3.579545MHz one, then lift pin 7 of the CXA1145 and connect to +5v. This only offers composite output.

 

 

 

I recently got a PC Engine and found the TGezRGB was not even close to fitting using the direct solder method. (see picture)

 

So now I'm working on a redesign specifically for the original model PC Engine.

 

Even though I'm going to use the same circuit, it will still require a complete redesign of the board.

 

 

 

 

Some folks put the rgb circuit inside of the Tennokoe Bank vs. inside the pcengine. This method also allows space for standard rca type connectors.

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I have the Turbografx 16 easy RGB mods available on my website for $39

 

http://www.lowbudgetify.com/turbografx-easy-rgb.html

 

I also ordered some PCBs for the Turbografx PAL to NTSC conversion.

Will be testing soon hopefully.

Dang dude, $44 s/h??? :???:

 

Edit: Nevermind. Price includes shipping... :lol:

Edited by stardust4ever
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  • 2 weeks later...
  • 3 weeks later...

I made a RGB / composite / stereo mod board for the PC Engine.

 

It is soldered to the bottom of the PC Engine motherboard over the expansion port pins.

Right now the easy installation method is only tested in the original white PC Engine.

 

It works great, I hope to have these available soon.

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post-31751-0-59613600-1441764711_thumb.jpg

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  • 5 years later...

It's been 5 years but since we know about the YUV color problem with RGB output, a proper PAL to NTSC S-Video mod board from low_budget is more needed than ever. :)

 

samiam was working on one on pcengine.proboards ( https://pcengine.proboards.com/thread/879/designing-video-mod-ypbpr ) when Furrtek extracted the YUV lookup table prompting Voultar to make his own Y/C S-Video circuit:

 

So, low_budget: would it be possible for you to revisit this with the goal of implementing one of the new S-Video circuits for proper YUV color? Getting something like this out of the PAL TurboGrafx without the dot-crawl issues of CVBS Composite Video is the new Holy Grail. :)

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