Hey all, it looks like there are some knowledgeable folks around here with experience with the CXA2075 chip. I have the chip wired up with a LM1881 and put together as per the schematic in the datasheet and I am providing the RGBS lines from a jamma connector hooked up to a CPS2 board. The image is on the screen, but its mostly in black and white, the picture occasionally drops out during the attract mode, and the screen is rolling on the title screen. I do get a stable black and white image when the game is actually playing. I suspect its the voltage on the RGBS lines?
Yeah, it probably is - the CXA2075 is designed to accept 1Vp-p signals on the RGB inputs and if it's much larger than that then it screws up the clamp circuit and you get video level shifts. Try to get it as close to 1V as possible - any more than about 1.3V causes problems.
Yeah, although you might find that the source impedance of an arcade board is higher than you expect - so if you made a correctly matched 4:1 75R voltage divider then the image could end up being pretty dark...
Notes on Operation Be careful of the following when using the CXA2075M. 1. Be sure that analog RGB signals are input at 1.0Vp-p maximum and have low enough impedance. High impedance may affect color saturation, hue, etc. Inputting RGB signals in excess of 1.3Vp-p may disable the clamp operation. I've used the CXA2075 as a direct replacement to the CXA1645 in a Playstation and it just worked there without any further changes. You have the datasheet? https://console5.com/techwiki/images/2/23/CXA2075M.pdf
Thanks rama and trimesh, ive made some progress with the CXA2075. i added 180+75 ohm as voltage divider resistors to the RGB lines and i got a color screen but the image isnt stable, so ive been playing with adding resistors to the sync signal to my LM1881. Ive had varying levels of success. Its either been: Perfect color, unstable image Stable image but in BW Stable image but in rainbow shimmer I really need to get some 1k pots, or else im stuck swapping resistors out of my circuit.
Should work fine in the PlayStation - the output range of the video DAC is about 1V, which is what the chip is designed to work with. A lot of arcade boards use R2R resistor ladders as output DACs, so they have a much larger swing (often up to 5V) - this isn't a problem in an arcade machine because they are direct driving the monitor and arcade monitors typically include pots to set the RGB drive levels. They also typically have quite a high input impedance (maybe 2-3k) - which is why most of the arcade boards aren't set up to expect 75R loads.
Yea, I didn't expect to run into any issues with the PSX. I was mentioning it to say that the chip is easy to work with and, given its obscure status, it actually does work On that note: The internal YTRAP is only so-so for the application. One can tweak the filter via a ~5kOhm pot but it doesn't really get rid of the color dot crawl around sharp edges in PSX 240p games. This works much nicer with the CXA1645, imho.
Um... I don't understand. What use is LM1881 on a CPS2? Wouldn't that be trying to strip composite video from a board that never output it to begin with?