Sega CDX rgb output... Static???

[retrofan]

I've connected a SONY PVM-20N5U monitor, to the Sega CDX rgb output.

I've used 3 x 75Ohm in series and 3 x 220uf (+ cdx side) caps on the RGB lines, and a 1k resistor on the sync pin 5. (image is bleeding/over exposing without this resistor)

However the problem is the RGB image seems to have some noise, more pronunced on solid blue colors. Static can be seen when very close to the monitor, and gives a feeling of unclean/noise output.

Another issue is some vertical lines that are displayed at certain times between game loads or while games change screens most of the time for a brief second but on the CD-ROM bios screen they seem to stay as you can see in the screen shot below.

Here is what they look like:

http://members.core.com/~drtooth/cdx/Vertical_lines.jpg

*I bumped up the contrast for them to be more visible*

I noticed that they dissapear  (in the case above) just as soon as the cdrom is about to load and go to the sonic sega screen.

This is very strange since it doenst appear to be a problem with cabling etc. since they are not there all the time.

I dont have any issues with any of the other consoles that I added use rgb with, snes, turbo duo, psx, ps2 etc. same monitor. (Sony PVM-20N5U with RGB circuitry enabled)

I have 2 sega CDX's and it happens on both units the same way.

I would describe the output I get as if some sort of interference from the machine
is causing it etc....

If anyone has an idea what is the cause of this please let me know.

Thanks,
-retrofan

[Aidan]

Could be interference from internal sources...

Your issue with the sync pin and overexposed signal suggests that the monitor is expecting composite sync rather than composite video on it's sync input. This may or may not cause other issues with the monitor display.

[retrofan]

Could be interference from internal sources...


So what you're saying is the CDX has a shielding issue ? And everyone would experience this on RGB ?

Your issue with the sync pin and overexposed signal suggests that the monitor is expecting composite sync rather than composite video on it's sync input. This may or may not cause other issues with the monitor display.

The monitor can take either composite sync or composite video it has sync splitter circuit inside. I tend to use the actual sync pins in consoles rather than comp video for sync.

However I'm using composite sync (PIN 5) .

Pin 4 is composite video. The overexposing doesnt occur since I've added the 1k resistor and a 100uf cap on the sync line.


Yes, it feels as if the CDX is leaking out noise or something, but I need others that use RGB with the cdx to let me know if they see any of these issues...


Something else interesting I've noted, I had a game with a full blue screen and while in the main menu I pressed the directional keys on the CDX joystick and noticed that "noise" changed also, changed pitch or was affecting the screen differently. Dgital noise ? based on what the cpu is doing? Very odd... Just like tunning a TV antenna... LOL

Again, you have to be 2, 3 feet away from the monitor to see this noise running in the background. And mostly on BLUE solid colors. Cannot be seen on black, white, yellow etc.. Just some dark colors, also cherry RED.... (Sonic Spinball)


Another thing I did, was removed a game cartige while system was on (I wont do this too many times), and noticed the static dissapear. Reinserted the game cart and it did not come back. However game was frozen. If the CDX is frozen there is no static. Even the vertical lines dissapear when the CDX freezes. Now if I reset the CDX the symptoms are back. Definatelly not cabling etc.
As long as the game is running/software is active the static and vertical lines can be seen... Some weird stuff...  Other than this the RGB out is nice and clear with good colors.

[Aidan]

Something else interesting I've noted, I had a game with a full blue screen and while in the main menu I pressed the directional keys on the CDX joystick and noticed that "noise" changed also, changed pitch or was affecting the screen differently. Dgital noise ? based on what the cpu is doing?

That's an almost definate indication that you're getting noise from internal sources. Possible reasons (without examining the system more closely) are poor power supply and degradation of filtering capacitors internally. Other possibilities include the possibility that the RGB output just wasn't designed very well.

Not surprising that the processor locked up when you removed the cart. You just removed it's source of instructions, and it carried on trying to access it. All it got back whatever was on the bus (probably 0xFFFF) and tried to execute it.  

[Computolio]

   My CDX has a bit of noise too. You may have to live with it, as the thing is way too cramped inside to mess with and way too expensive to replace.

[kendrick]

It's interesting to observe that the A/V port on the CDX is over on the right side of the device, rather than poking out of the back. This wouldn't be a problem except that it's right underneath the CD lens mechanism, which I would imagine is the main source of your interference. This isn't an issue on other Sega CD-compatible units, where the A/V port is shielded and way far away from any part with a motor or other component with radiant interference. If RGB output is important to you, you should invest in a Sega CD or X'eye unit and reserve the CDX for portable uses.

-KKC, digging on the Nokia N-gage. It's more of a portable Playstation than the PSP is, in my not very-damned-humble opinion. :)

[Vertigo]

Why don't you try getting hold of something metal the correct size to clip around the A/V port in an attempt to shield it from the interference it's getting? make sure you electrical tape around the metal thing so that it doesn't short anything else though, to not do that would be stupid.

[NFG]

I would suspect, friend vertigo, that the problem is electrical interference, not radio interference, and you'd have more luck cleaning up the electrons than the..   um...  radions.  

Shut up.

[Segasonicfan]

I have noticed this problem a lot lately and it is driving me nuts.  I've got a couple CDXs and they've all had this problem...and it's a crying shame to see the noise on a beautiful 36" RGB monitor.  The noise from my RGB seems to be light vertical lines rolling across colors...anyone else notice this as the same problem?

I"m going to look into this more thoroughly and hopefully come up with a solution.  Isolating the RGB lines from the chroma encoder may help, I guess I'll see what I come up with.

-Segasonicfan

[Segasonicfan]

ah, found & fixed the problem.  It seems the power supply is mostly to blame which is not too surprising I guess.   I'm figuring that since the power supply is a DC-DC conv one (the only one in a Genny model I'm aware of) that it has to sacrifice some regulation.
anyway, all it takes is a 7805 installed like most gennys.  It's a little bit tricky knowing where to split the power line and do it, especially if you don't want to use the 7805 to regulate the entire +5v load (and you don't have to).

If anyone's interested I can post a little how to for it.  This mod fixes the problem to make near-perfect video.  There is some *very* slight noise that can only be noticed on extreme examination but as a fellow mentioned over here http://board.kohina.net/viewtopic.php?p=5770&sid=51c8168928058b6128c904a0167d193b the 315-5660 mixes the sound chip into it so it causes some extra noise.  Very. very hard to see after this fix though.

-Segasonicfan