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View topic - Game Gear - now in PAL 50hz mode! But need help for TV out

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  • Joined: 05 Jan 2006
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Game Gear - now in PAL 50hz mode! But need help for TV out
Post Posted: Sun Mar 16, 2014 9:41 pm
Hey all,
I've been wanting to put a GG in PAL more for some years now and I'm very excited to have accomplished it this week for the first time. As far as I know no one has ever been able to do it.

Well, thanks to the wonderful schematics dumped over here
http://www.smspower.org/forums/viewtopic.php?t=14053
I was able to fiddle around and put the GG into PAL mode. Pin 119 (on a single ASIC 315-5535) is labelled as "SECAM" in the service manuals. Simply cut the trace to ground and apply +5v through a 10k resistor and...GG jumps into 50hz PAL mode! Now we can enjoy the full library of SMS games on a GG.

There are more than a few games that dont work without this, including Taito Chase HQ, New Zealand Story, and many others.

Now the bad news: this mode is not compatible with any of the TV output mods available (!) It's very odd indeed, but when put into SECAM mode the GG no longer outputs standard SYNC signals, through T2 (CSYNC) or through HSYNC and VSYNC (pins 101 and 102 on the 315-5535). The screen simply starts rolling. My guess is that the GG actually changes its clock signals to go into PAL mode, which then throws off these outputs. Any ideas? The GG screen still has sync so I was hoping maybe someone would know how to make a DAC or something for the sync that the internal LCD uses.

Any ideas on that would be much appreciated! I'm looking forward to having a 100% universal GG Master System :)

-Segasonicfan
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Post Posted: Sun Mar 16, 2014 10:42 pm
Not a true solution, but do you have an older television that has adjustments for VHOLD and HHOLD? You may at least be able to fake it and tune in on the non-standard sync.

Also, I don't live in the EU but I believe SECAM is mostly related to France and not the same type of PAL signal used elsewhere. This may be part of your issue.
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Post Posted: Mon Mar 17, 2014 12:59 am
Last edited by segasonicfan on Mon Mar 17, 2014 2:18 am; edited 1 time in total
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SECAM is mostly related to France and not the same type of PAL signal used elsewhere. This may be part of your issue.


thanks for that info, you make a very good point. What I am puzzled about is how the Sync should be affected at all preencoder stage. I know PAL/NTSC/SECAM are signals with different sync outputs once they have been encoded, as is the case for the different circuits used in game consoles like SMS, Genesis, etc. where the CXA1145 and CXA1645 have different TTL clock signals for the different modes. But that's only at the encoder stage, the "pure" RGB + CSync going in is always the same.

I'm going to try using a ISL59885 which is like a fancy LM1881 to see if that helps. I already tried a JROK "sync cleaner" board to no avail: (http://www.jrok.com/project/sync_cleaner/sync_pics.html)

EDIT: ISL59885 also didn't work :( It looks like the VSYNC is definitely the problem, but I don't know how to convert it from (the likely) 50hz to 60hz without some fancy video decoder circuit like IR3Y29M or similiar. and that would be a real pain in the butt to cram inside the GG.

-Segasonicfan
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Post Posted: Mon Mar 17, 2014 2:17 am
Still interested if you can fake it with using the h-hold and v-hold adjustments on an older television set.

I have been able to do that myself with some 1970's era sets to switch between 50 and 60hz on systems.
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Post Posted: Mon Mar 17, 2014 2:20 am
possible, I just dont have any of those around though. Best bet would be to try on my friends arcade cabinet after I repair it (it needs a cap kit to fix the chassis)
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Post Posted: Thu Mar 20, 2014 6:37 am
It has been a while since I cracked a gg open but is there not a crystal on the board? I think it is 3.58mhz would swapping to 4.43mhz help? Just an idea.
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Post Posted: Sat Mar 22, 2014 7:13 pm
xtal is something like that... i highly doubt that would do anything since the clock signal is split inside the ASIC to make CCLK and VCLK. The video clock is what would need to be messed with (maybe) and that can only be done without screwing the other stuff on a 2 ASIC model. Looking to buy one now.

What I need to do is look into it with an oscilloscope and such tools to see what its doing. Even a decoder wont fix this sync, so frustrating to be so close yet so far! Ill post some videos later too of the issue in action.
thanks for throwing out some ideas.

-segasonicfan
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Post Posted: Mon Apr 07, 2014 11:59 pm
Well I swapped xtals and had nothing promising happen.

FYI, the game gear runs on a 32.2mhz crystal....this is divided internally (in the 1 ASIC) to 3.57 for the CPU and cart clocks and (I assume) the needed 10.7mhz for the VDP (video processor).

So I have it a master clock of 32mhz, 30mhz, 27mhz, and 40hmz. All still have the Vhold going wacko after the PAL switch.

I still don't understand it entirely, but I think "PAL mode" might simply be an underclocked VDP. That would explain why PAL games run in NTSC but with glitches. So the mystery is, why does underclocking the VDP affect VSync? Does it do this on a regular SMS2? I kind of doubt it. I could run the thing through a CXA1145 or equivalent to see what happens, but my guess is nothing will come out with a screwy CSync going in.

pin 118 is "NTSC" and when this is set to logic high that is what makes it PAL mode (underclocked VDP and sound, too). But next to it is a "SECAM" pin which apparently doesn't do anything (I had them mixed up before). Grounded or +5v this pin has no effect I can tell. Though according to the SMS2 schematics, there is a "SC" pin, presumably SECAM that outputs 4.44mhz for the CXA1145. I wonder if this pin is the same thing in the GG? It would be odd.

Running out of ideas but what I can think of left is:
1) measure the VDP clock the is labelled on the ASIC (apparently going to a capacitor (C5) which is left missing). I'm assuming this is a pin for measuring purposes of the VCLK since it does nothing else.

2) try this on a monitor with adjustable Vhold and see what happens

3) measure the sync on an oscilloscope (don't have one, but can maybe find one to use) to see what's going on.


Any more ideas would help greatly. Specifically, how does sync work in the GG LCD? Since the LCD works in either mode, I'm pretty curious about that.

-Segasonicfan
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Post Posted: Tue Apr 08, 2014 12:11 am
AND here's a video of it finally:

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Post Posted: Tue Apr 08, 2014 12:42 am
The SC pin is subcarrier output. And it should switch between 3.579545MHz and 4.433619MHz.

However the master clock is NTSC subcarrier * 9, and there is no way to get PAL clock out of it. So the PAL mode must have some kind of different master clock in use. 31.035333 is a good starting point.
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Post Posted: Sat Nov 04, 2017 1:04 pm
Sorry to reply on this old thread but I'd like to ask something about this mod. Do the 118 pin of the GG system on chip must be cutted coming out of the chip or the trace itself that enter the chip? If I want to create a button of this mod I just switch from the usual trace 118 pin connection switching to the 5V itself?
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Post Posted: Sat Dec 02, 2017 4:51 am
You just have to cut the trace's connection to GND or 5V, wherever your system connects it. Then add a 10K resistor to +5V and a switch to ground.

You could also control it with just a button using a latch circuit, like the one on my Multi Use DIY board:
https://segasonicfan.wixsite.com/retro/store

-Segasonicfan
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