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Sep 11, 2020
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Hi all,

You may have seen my other threads about being scammed on an OR2 cab that came with 15/24k monitors not the standard 31k monitors. Anyway I thought fine I will just use my 8100 VGA to cga converter which works a treat on my pc, however it doesn't like Chihiro input I think this because the chihiro outputs a horizontal sync only and perhaps a composite sync on green.

I'm thinking there are 2 possible solutions could I use a lm1881 or EL4583 to separate the sync into h and v that the converter board might like better.
  • Use the 15khz output from the Xbox av port directly while tricking the game thinking it's still 31khz.
Has anyone had any experience with attaching a Chihiro to a 15khz monitor?

Thanks all
Could a mod move this to the Chihiro forum I didn't notice it in my haste to post it,thanks.
  • Use the 15khz output from the Xbox av port directly while tricking the game thinking it's still 31khz.
XBOX dont have 15khz output, the lowest output is 480i...so I dont understand why play with 3D game coded for run on HD CRT (480p). if it's for scanline, is useful for 2d game before 2000...after for exemple marvel vs capcom 2, game thinked for 480p/31khz.
thx So 31 is 480 p and above. But I assume that @Herc187 looking for scanline and same with 480i does not.
No the Chihiro itself won't do 15khz there is talk of dip switches in the filter board that can be switched to force 15khz but I couldn't make it work also games won't boot with it set to 15khz. The Chihiro has the Xbox signal passed into the daughter board that then turns it into 31khz VGA. So I'm thinking that I must be able to tap that rgbs of Xbox signal and use that or pony together something from the Chihiro VGA output that the cga converter likes.
The dipswitches are mostly meaningless, the games themselves will reset the view to what ever they're actually coded for (being 480p for every available game). You *can* have SEGA-boot ignore this by changing the `videoMode (+0x2C)` in the `boot.id` of the game your transferring but it wont stick when the game loads.
If you look on the baseboard you will notice that there is already an lm1881 to extract the composite sync from the green color signal. So if you think a vsync would help your converter all you need to do is solder a wire from that lm1881 vsync output pin to the vsync pin of the vga connector.
I have tried this but didn't got an improvement on my monitors that didn't work with the chihiro.

Another issue that can cause trouble is the fact that the video circuits are powered from the 5V that comes trough the avip cable from the main board video connector. That is a very noisy 5V. So if you cut that pin from the connector, you can power those circuits from a separate 5V. (I still need to construct a small pcb that uses the 12V and makes 5V from it with an 7805. I have a proof of concept that this mod improves the image quality on most monitors.

Also note that the chihiro base board is seen as a scart RGB by the chihiro bios. Dipswitch 6, 7 and 8 on the filter board allow to change this behavour.

Even if you would be able to have an rgb 15kHz signal, the video levels would still be 0-1V so you would need a video amplifier to get them to 0 - 5V

I assume a 32" lcd showing it's picture in letterbox mode (black border left and right of the screen covered with the bezel) isn't an option either? Last time I checked most screens are just half an inch to large to fit.
It could be the lm1881 doesn't output a h sync and some picky monitors need a clean h signal as well as a v sync. I have a lmh1980 on it's way that provides h and v sync to see if that would do it. Funnily enough I have a GBS 8220 as well cga to vga converter if I hook that up in front of the 8210 it works! Not the greatest picture quality but certainly playable.
lm1881 indeed only outputs composite sync (on the vga hsync pin) and vsync (unconnected on the chihiro base board)
my tests with the LMH1980 were not much more succesfull.
I used a scart rgb cable and it wasn't having separate shielded color wires, so there was a lot of noise and crosstalk between those signals.
Maybe that's the reason why it didn't work well. As usual, I hope to be proven wrong and I hope your results are better.
Looks like you tried all permutations does the Chihiro output a 15khz signal into the video board ala Xbox with a hacked bios or does it scan double a 15khz output?
That's a difficult question. The type 3 needs segaboot.xbe to run as it uploads the dimm firmware.asic file.
The bios isn't seeing the dimm game area untill that firmware is running.
segaboot.xbe only seems to run if the avip is seen as scart rgb.

It would suprise me if the game would switch it's videomode when it's started. Setting the correct video mode is something the dashboard is supposed to do.

So, if the games would run in a 15khz resolution is a bit hard to say. You would need to be able to start the game without segaboot.xbe first.

OR2SP needs a partition on the dimm for it's high scores and settings. There also is a partition that's needed for the networking. (something you also need in an outrun twin.)

So maybe the best option would be to switch the videomode after segaboot.xbe had started...? Or hack a kernel so that it switches to another videomode instead of the 640 x 480 segaboot.xbe is setting up.
I don't know why that would surprise you (games switching video modes). I already told you that only segaboot cares about the boot.id "set" video mode (and setting 0xFF makes it accept everything) and the games will reset the view to their required resolution.
So I tried a few different ways and pretty much found what you did it's always quite wavey and not really very good. At the moment I have one cab hooked up with an Xbox RGB cable to a RGB to VGA converter then from a VGA to rgb converter. Not great but I have only one Chihiro AV cable ATM. In the other cab I have the VGA 31khz output going to my VGA to rgb converter but with a lm1881 separating the sync now the board likes it....but still not great with a course waveyness over it.
if the problem you are having with the quality is the same as mine, it should show up very clear when you go in the test menu to the clock setting menu.

You can improve that issue with a voltage regulator. The base board video circuits are getting their 5V supply trough the avip cable. You can cut that pin on the base board avip connector to isolate it (it's one of the outer pins) and feed it a proper 5V from a voltage regulator. I use an 7805 that I supply with the 12V supply rail from the main board. (I decouple the regulator output with a 10uF capacitor as well.)
I can say this fixes the issues I am seeing on the clock setting screen for 90 - 95%
Just let me know if you need more information about this mod. (Assuming you are seeing the same issues.)