Chihiro vga output

[obcd]

Today, I tried to reverse the chihiro base board vga output.

I noticed an lm1881 on the board which is pretty much what people used for Frosty's VGA cable on the xbox.

The chihiro circuit is more complicated. Pin 5 of the LM1881 drives a 4066 analog switch that turns off and on the video signals.
The video signals are also amplified and buffered twice with a video amplifier ic.

2 of the dipswitches on the filter board control the id bits of the main board video connector.
On a xbox, these bit's are used to figure out what video cable is connected. Both are on which is consistent with vga.

Another dip is used to switch the input of the LM1881 to either the green color signal or the composite video out signal.

The strange thing I notice is that the VSYNC output of the LM1881 isn't connected to the db15 vga plug.
The LM1881 seem to output composite sync on the hsync pin (according to it's datasheet)

So the question...Should a pc tft monitor work with such a signal or does it need a vsync?

Google doesn't have the answer. Some monitors should work with composite sync on hsync only. Others don't seem to work.
A third category does work, but not when the vsync is connected as well.

Maybe some of you guys have tested their chihiro with a pc monitor and can confirm it should simply give a picture?

 

[aoiddr]

Some monitors and TVs with a VGA connector will work and some will not. I know that the Samsung SyncMaster 2253LW can take a Chihiro signal with zero issues and gives a perfect picture, but some other monitors are not so lucky and will just give a black screen. It's a crapshot.

One for-sure way to get a signal is to pass it through an XRGB unit...like the XRGB-3, which will output the signal correctly to anything, but it's a very expensive solution.

Another option, which is far from perfect, is to try one of those cheap chinese CGA-to-VGA video converters like the GBS-8200 / GBS-8220. The Chihiro signal has a "whitewashing" problem where the screen will start dark and get bleached white after a while. You can play around with the Clamp settings to try and correct this...
CLAMP ST = 43 (I think anything between 42~49 might work)
CLAMP SP = 0"
It's not perfect, but the picture is of aplayable quality without the color changes and having to reset it every fewminutes.