Dreamcast+KVM

[zakk23]

I've got a WG D9200 that I use in my arcade cabinet. I have a variety of input devices that I use for this cabinet, so I figured a KVM type switch would be a good idea. I've tried multiple switches, and all exhibit this exact same problem. Here's what I have hooked up to it:

1) RGB video output from the Jamma harness in the cabinet. Directly wired to a VGA connector, no inline resistors etc.
2) VGA out from a PC (640x480)
3) RGB via a component->RGB converter. No scan conversion, so scan rates are passed thru.
4) A dreamcast VGA box, in 31khz mode.

#3 and #4 intefere with each other horribly. I can see a rolling (horizontal) image of the dreamcast if I've got #3 selected as the active input. It's a bit subdued and 'background' but you can distinctly make out the 'Dreamcast' logo on bootup etc. If the dreamcast is the active input and #3 is powered up and providing signal, there's a rolling 'dark/discolored bar (again, horizontal)' on the screen.

Dreamcast also interferes with the PC VGA, no 'shadow' image, just a rolling 'fuzzy' bar. #3 also inteferes with it, but it's a solid thin discolored/darker horizontal bar

Interestingly enough, I don't see any interference the other way, i.e the dreamcast image is clean if just the PC is plugged into the KVM, and the #3 image is clean if it's just the PC and it on the KVM.

The Jamma RGB input causes no ghosting/artifacts on any other input when it is active.
the dreamcast causes fast diagonal 'wavy' bands on the Jamma RGB, and the #3 input causes the same pattern, just really faintly. (almost unnoticeable).

If any two inputs cause some sort of interference with each other, it occurs if they are the only two items on the switch, and does not change if the ports are shuffled around. This has occured on multiple KVM switches, multiple displays, multiple DC Vga boxes, etc.

If I plug in just PCs to the switch, all is fine. No problems. Even at higher than 640x480 resolutions.

Any ideas what's going on here? Does the switch not like the mixing of different syncs? Is the dreamcast too "hot" and this may go away if I place some resistors in strategic places? Anyone using a KVM with a dreamcast+PC? Specific brands I should look for, etc?

[edit: I forgot to mention, i've tried different cables, including ones with ferrite "shields" etc. Same thing]
-=Zakk

[StephenH]

The component -> RGB converter may be outputing a 15KHZ signal, in which the others are 31KHZ or higher.  I am not sure if the KVM's internal electronic sensors of what is in use regonize the 31Khz signal, and switching back may be what is causing confusion, as many of the others are 31Khz.  The original JAMMA board would likely be 15Khz or possibly 25Khz, depending on the game.

Here is what you might be able to do:

1) Use an upscan converter with the JAMMA board and Component to upscan the JAMMA and Component video to 31Khz.

2) Get a video card with component TV in.

3) Take back the KVM switch, and get a MANUAL printer data switch, and make your own 15-25 pin cables with the pinout the same for all, or see if there is a model of KVM that can switch the entire 15-31KHZ range.

[zakk23]

Nah, that's not it. I get interference if I just have a PC and a dreamcast hooked up. and then only the PC input has interference, the dreamcast one is fine.  Really the dreamcast is the major offender, and the component->RGB is minor interference, but still irritating. That converter ends up outputting both seperate and sync on green simultaneously, and I'm wondering if that might be the cause of some minor problems when it's involved.

Responding just inspired me to try something. I realized I had a VGA splitter cable, so I split the dreamcast output, one end going to the KVM, and another going to an RGB capture card I have. This reduces the brightness of the dreamcast image quite a bit, and I must say, without that reduction, it never occured to me how insanely bright/strong that image was. Anyways, when it's split like this, it doesn't interfere at all with other inputs, guess that's a start.

Looks like I should reduce the levels on that dreamcast output a bit, and potentially the  RGB->component also. (and jamma too, that thing is wayyyy too bright, which is understandable). Does anyone make small VGA cables/adapters that'll do this, or am I better off grabbing a few packs of resistors and VGA ends and making this myself?

[stellarola]

Maybe this might help, I made this a few weeks ago. It's how I hook a PC and Dreamcast to my arcade monitor...

You'll want to save the file to your computer to view a larger image.