Sony PVM distorted using RGBS input

I have a small 14" Sony PVM monitor for RGB gaming and when I use the RGBS input from a MVS board I get weird ditsortions when the screen is really bright.

I have a little box I built that converts SCART to simple Phono plugs so I can use normal cables to plug into the PVM (it has BNC connectors on the back) The box also has little screw terminals on top to hook bare wires from a Jamma board to the box to use jamma boards on the TV without wiring up real cables.

There is really no real circuitry in this box, just jumpers to transfer signals from the SCART plug to phono jacks. The case is aluminum and grounded so I didn't run dedicated ground lines for everything (could this be a problem?)

Anyways when I hook a MVS board directly to this box I get weird stuff going on where bits of the image kind of distort to the left. This is really noticible on the crosshatch pattern. The horizontal lines look fine but the vertical lines are all crazy and wavy. This goes down a bit in games but there is still some of it. A lot of text looks slightly distorted in this way (round timers, score). You can kind of see the distortion increase as the screen brightens.

It isn't really terrible anywhere but the crosshatch, and i don't notice it in most games, but it's annoying anyways.

Any ideas?

Try a pot on the sync line.

any particular value you suggest?

I'd say 500ohm.

Yeah chuck a 500 ohm pot in the line and if it works measure the resistance that it works at and replace it with a resistor.

well no 500ohm pots lying around but I tried a 100K in very small increments and various 10-500ohm resistors and nothing happened except that with enough resistance I got a crazy rolling picture. Even the 100K pot would produce the same slightly distorted image for about 1/8th turn before jumping right rolling.

Could it be my TV? When I have the Neo plugged in and the PVM on RGBS mode even the menu is warped. I'll test a bit with my Sega Genesis running through RGBS but as I remember it worked and looked fine.

play with the +5v

Pics dude.

A sync cleaner might help. For $10 is worth trying.

Ok, I think it may be my TV not liking the high RGB levels a MVS board puts out.

I didn't get around to messing with the 5v, but I did try messing with the sync some more but no difference until I go far enough to get a rolling image. There is no gradient to it, it looks exactly the same, with the mild distortion until it jumps right to rolling.

I did however try adding some resistors to the RGB lines and I found that if I lowered the RGB levels the distortion went away. Although not 100% unless I went really low, 220ohm resistors on the RGB lines pretty much eliminated the distortion. 470's eliminated it entirely but things looked a bit dark. There is maybe about 1px or so distortion on the crosshatch screen (which was always the worst example) but in game its pretty much perfect. It also seems to help the cut-off you see on the right side of the screen (in particular on the SNK logo in the RGB test screen pictured below).

It's not as bright and vivid with the 220's, but I played Last Blade for awhile and got used to it. I can't tell if its a bit dark now, or I just got used to how vivid it was before.

Anyways, Here's 2 good examples of what I was getting without the resistors on the RGB lines.

Where would one get a sync cleaner? Would it help (or at least be a good idea) even if things generally seem to be working fine.

Would it be good to have if I'm going to be plugging this into many different TV's. I personally own a 14" Sony PVM for testing stuff and general fun, and a 34" Sony XBR for my main TV. With two CRT's I can be sloppy with sync signals but I'm sure I'll take this to other people's houses who have LCDs and I hear those can be picky.

Hewitson said:

A sync cleaner might help. For $10 is worth trying.

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