When RGB becomes GBR

Started by RGB32E, June 20, 2005, 06:23:44 AM

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RGB32E

Have any of you out there encountered problems with encoding the RGB output of some (most) arcade PCBs?  One of my NTSC encoders (AD725 eval board) works fine with Capcom PCBs (except CPS3), but doesn't work properly with most of my collection.  The problem is that the color components in the resulting composite/s-video signal get shifted (i.e. RGB appears to become GBR).  Some of the games that have this issue are Double Dragon, Cadash, Bionic Commando, and CPS3.  The games that work fine include Strider, Strider 2, Final Fight, Street Fighter 2, Street Fighter Zero 2 Alpha.

So, if anyone else out there has encountered this issue first hand, and knows how to resolve this, please let me know.  All of the PCBs work fine when connected to an RGB monitor, so it isn't an issue of the PCBs not working.  I'm guessing that it might be related to the composite sync.  I have looked through some of the PCB manuals, but no information about the RGB output is given.  Thanks.

NFG

One of the biggest problems is the over-bright signals put out by most PCBs.  It overwhelms the encoder and the result is unpredictable.  Sometimes I get only a green screen, no image, unstable sync, image curl...  

RGB32E

Well... increasing the resistors used to drop the voltage of RGB signals did not solve the problem.  The encoder I am using is an Analog Devices Evaluation Board.  It is a strait forward application of the AD725 RGB encoder IC.  

As RGB signals enter the circuit, there is a 75-ohm chip resistor to ground.  For CPS1/2 and Sony PCBs, using 250 ohms of resistance in series on the video signal results with a picture that rivals home consoles (YC).  Upping the series resistance to 500k ohms didn't correct the problem I am facing.  Do you have another approach to lowering the voltage?