Guide - Modding your Dreamcast VGA Box for 15/31KHz output

PCB problems and fixes
leonk
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Re: Guide - Modding your Dreamcast VGA Box for 15/31KHz outp

Post by leonk »

Sorry for the old thread bump but I have a question that fits here ...

I have a NAC with an Ms9-29A (15/25) my hope of finding an Ultracade UVC to convert 31khz to 25khz is nil at this point, so I wanted to do this mode to force DC into 15khz and swap between mame and DC on my cab for the newer games.

My question: would all/most games play fine in 15khz or would only a few on my USA NTSC region free DC?
antron
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Re: Guide - Modding your Dreamcast VGA Box for 15/31KHz outp

Post by antron »

Does anyone know if it is possible to force DC 480i games to 240p with any sort of patch? I am aware that 3S has this mode, but what about for others like CvS2 and other NAOMI ports?

Thanks in advance,
antron

EDIT:
It appears not. I am really surprised at this, given how many games can be forced into VGA with a simple patch.
antron
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Re: Guide - Modding your Dreamcast VGA Box for 15/31KHz outp

Post by antron »

I have some information regarding the Third Strike patch shown in the first post. I found that this game would not display in RGB with my USA Dreamcast unless I applied this patch. My guess is that its need had only been reported in Europe because almost no one in North America used RGB.

And I have some more news. The same problem exists for the US version Gunbird 2 (at least with the release I used). But you will only find and need to replace the 3rd and 4th Hex codes given in the first post of this thread. This port seems to have been handled by Capcom, which explains why the same patch works.

antron
EazyE
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Re: Guide - Modding your Dreamcast VGA Box for 15/31KHz output

Post by EazyE »

Does the Capcom I/O need its own power for it to work with this? And would the Sega I/O work as well?
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skate323k137
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Re: Guide - Modding your Dreamcast VGA Box for 15/31KHz output

Post by skate323k137 »

Mega old thread but just wanted to thank OP. This got me up and running with bangai-o!
TheSpaniard
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Re: Guide - Modding your Dreamcast VGA Box for 15/31KHz output

Post by TheSpaniard »

Would be great if this thread had photos reuploaded lost from photobucket.
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thchardcore
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Re: Guide - Modding your Dreamcast VGA Box for 15/31KHz output

Post by thchardcore »

Might seem like a stupid question, but please bear with me.

I did the normal switched 15khz/31 khz mod to my VGA box. Assuming I want to use my scart switch to OSSC for the 15khz, I wired up a VGA to SCART cable as follows:

- 220uf caps on RGB, positive leads facing the VGA box.
- 220uf cap and 470ohm 1/4w resistor in series on H sync (VGA pin 13). I left V sync disconnected.

Plugging the cable I made into the VGA box with switch set to 15khz and checking voltages with a meter before connecting it to my switch/OSSC, I get normal (300-400 mV) output on the RGB l lines but I am reading about 4.5V on the sync line. I stopped here.

Will what I am doing work or do I need to add a sync circuit to grab composite sync/video from the H sync? Also, does my voltage seem high for sync as wired or is it simply because I am reading it without load?

Any help is appreciated.
15khz upscaled is cheating
filevans
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Re: Guide - Modding your Dreamcast VGA Box for 15/31KHz output

Post by filevans »

dmauro wrote: December 17th, 2008, 5:13 pm Important Note:
If you're doing this mod, there's a good chance you're looking to play SFIII Third Strike in 240p, but the American and Japanese versions have some sort of video protection that won't allow the game to run in RGB mode on a PAL console. You will simply boot into a black screen without applying this patch to the disc image:
1) look for
09 00 09 00 09 00 09 00 09 00 30 88 07 89 06 A0 09
replace it with
07 89 32 88 07 89 33 88 07 89 30 88 07 89 06 A0 09

2) look for
00 E0 00 E0 04 7F 26 4F 0B 00
replace it with
02 E0 00 E0 04 7F 26 4F 0B 00

3) look for
30 E0 02 2E 00 E0 26 4F 0B 00 F6 6E
replace it with
4C 84 02 2E 00 E0 26 4F 0B 00 F6 6E

4) look for
07 D3 31 60 19 40 03 C9 02 88 00 8B 03 E0 0B 00 09 00
replace it with
22 4F 06 B0 09 00 26 4F 03 E4 19 40 09 24 0B 00 43 60
hello, I get the same no signal on RGB SCART on Dead or Alive 2 LE (JAPAN) as I get on SF2 3rd Strike and I tried using these condes on DOA LE and it didn't fix it, do you know a way to fix that game to work with RGB 15khz? thanks a lot
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dmauro
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Re: Guide - Modding your Dreamcast VGA Box for 15/31KHz output

Post by dmauro »

filevans wrote: March 22nd, 2021, 10:32 pm hello, I get the same no signal on RGB SCART on Dead or Alive 2 LE (JAPAN) as I get on SF2 3rd Strike and I tried using these condes on DOA LE and it didn't fix it, do you know a way to fix that game to work with RGB 15khz? thanks a lot
I happened to log in to see this relatively fresh, but unfortunately I don't have a good answer for you. I've never had a problem with simply not getting a signal out of the VGA box. Typically the problem you'd encounter would be you'd get 480i when expecting 240p, but for no signal at all... I don't know, sorry.
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