S-video is better looking on my monitor than RGB, why?

[Jack Burton]

So I am playing this game called Twin Cobra in the score comp.

I downloaded the psx version of the game and connected it to my main monitor, my mitsubishi AM-3501R.  The PSX version is just an emulator and runs the game in it's native resolution.

It looked very very good.  Very bright and vibrant and sharp.

Now, for some time now I've felt that the video on my S-video inputs looked brighter and more vibrant than over my RGB inputs on the back of the monitor.  

So I connected my computer and fired up Twin Cobra in advancemame in native resolution and switched back and forth between the two.  Sure enough, it looked much more colorful and had better contrast over the S-video.

What's the deal here?  This monitor is not an arcade monitor, and I'm not sure what those RGB ports on the back are even for.  

Here's the monitor in question:




not my own pics, but mine is identical

Is there some kind of adjustment inside to increase the brightness of the screen without losing my black levels and making things foggy?

Do I need a video amp for the signal from the pc?

I have opened this monitor and adjusted the screen control.  It was a little dim even on the S-video.  I used a Terminator DVD to calibrate the gamma adjustment in back and it looks perfect now, but the RGB inputs are dim.  

[Jack Burton]

I'm thinking about getting this:

http://www.ultimarc.com/vidamp.html

Going by the description I've read on this website and a couple of others I think I may have the dim screen that some arcade monitors have.  I have no clue why this may be the case on this monitor, but I suppose the monitor may only amplify over the s-video channels.

The monitor does have a switch on the RGB inputs for each color that switches between 75 ohms and high mode.  High mode brightens the image considerably, but also causes the whites of the image to become too bright and messes up the coloring.  I believe this setting is only for when using video output at the same time.

[MonMotha]

That switch changes the "input impedance".  Basically, there is a resistor to ground on the input that's mostly used to terminate the coax cable and prevent something called transmission line artifacting.  It also helps reduce current mode noise that the cable may pick up.

75 ohms is correct when using a VGA output from a PC (no matter what the timings).  If you want to drive the set from an arcade board, you may want to use the "high" setting, but then I don't know what signal levels it would expect into that Hi-Z input.

[Jack Burton]

So I opened the back of the monitor up again.  Wow that was a lot of screws!

There are seven different boards inside.  On the CRT cage there is a guide that shows where the video amplification board is. 

On it there are three little metal cages with components inside.  I can't really see what's in there.  There are some capacitors on the sides of the board.  No adjustments anywhere to be seen.  I wouldn't mess with them anyway.

So I don't think there is any luck to make an in-monitor adjustment.

Will a video amp help here or will it just do the same things as High impedance mode?

I'm thinking of getting the one from ultimarc, but it has video out on screw terminals.  I would much rather just get one that has db15 on both ends. 

[MonMotha]

Most professional and PC monitors are designed for 0.7-1Vpp signals into 75 ohms just like your PC outputs.  An amp would likely just blow it out like the high impedance input mode is doing.  The Hi-Z input mode will effectively double the input signal levels by removing the divider formed by the back termination on the PC output, so there's no reason for me to believe that a voltage amp on the video won't just do the same thing.

[Jack Burton]

If it is supposed to accept 0.7-1Vpp into 75 ohms why is it so dark then?  I have a Sony PVM 12" monitor that has the same 75 ohm/High switch on the back and games look perfect on it in 75 ohms mode.

I could understand if it was just a weak CRT, but I know it isn't because the video looks great over S-video.

Maybe if I could just amplify the video a little bit.  High mode is doubling the signal?  Maybe it would be better to do something like 1.5  High mode looks almost right, it just washes everything out like when you set contrast too high.  It also destroys black levels. 

[MonMotha]

Many monitors have independent settings for each input.  It just sounds like brightness/contrast are set wrong for your RGB input.  All that brightness/contrast effectively adjust are the expected black and white levels of the input signal.

No adjustments at all anywhere?  Are you maybe missing a remote control that would give an OSD for adjustments?

[Jack Burton]

There are a set of adjustments on the front of the monitor.  

It allows me to adjust contrast, brightness, color, tint, and sharpness.  It also has H/V size and positioning.  

There are three other controls too

AFC high/low
Notch
Noise Reduction

I have turned contrast and brightness all the way up on RGB and it still looks bad.  If I turn the brightness up very far it gives a servicable image, but it is very foggy and the contrast is bad.  There are no good blacks and the colors are washed out.  

I don't have the remote to this monitor, but I've seen it and it only had the same controls as those on the panel.  

It does save the differences in image settings between each input.  Also saves the h/v size and positioning.

This monitor has an input for TTL on the back.  It is over a 9-pin D-sub connector.  There is a knob next to this connector that is labeled "16 colors contrast".  It does nothing when I turn it on the rgb connections.

Might this input and knob be useful somehow?  I know TTl is a digital format, but perhaps the monitor will also accept analog signals over the input. 

[MonMotha]

The TTL input would be for the old EGA and CGA PC output standards.  They ran at 5V signal levels generated using actual TTL outputs rather than a buffered DAC (hence why they had such limited color depth).  Wouldn't be suitable at all for a modern PC output.  Might be suitable for direct connection to an arcade board, though (which still use the higher TTL levels even for analog video for historic reasons).  You could potentially try using this input with an amp to crank the analog VGA levels up to TTL levels, but it seems like something weird to do.

Turning up brightness too high will wash things out since black will become gray.  Turning up contrast too high results in blooming, but it sounds like you're unable to turn it up enough.

AFC, Notch, and probably Noise Reduction would be for the NTSC modulated inputs.

Dunno, perhaps this monitor just expects really strange signal levels or something is broken.  Analog RGB over the HD15 connector is a de-facto standard going back into the broadcast television industry in the 80s or even earlier and has always been at 0.7Vpp or 1Vpp when embedded sync is included, so I don't know what else it would expect.   Got a manual?  You can try using a video amp, but I suspect it'll just blow it out even worse than changing that termination setting.

Some TVs apply strange filters to their "television" inputs but not their PC inputs.  These filters can cause an artificial sense of "vibrancy" or "brightness".  What they're really doing is displaying an incorrect image to make it look brighter.  Perhaps that's what's happening for your S-Video input, and your RGB input is just correct?

For grins, change the termination setting to "high" and turn contrast down to see if you can get it to stop blooming.  Technically, this is "wrong" and you'd end up overdriving things, but it may do what you want.

[Jack Burton]

MonMothma, I believe you have solved it.  

The S-video input must be overamped or something like this.  I have no read in several places around the net that S-video and Composite signals are brighter than RGB.  This may also be contributing to this.

I left this monitor on for about 3 hours in advancemame, and even though I have to set contrast to maximum and brightness up about half way it does look really really good.  Still beats 99% of arcade monitors I've seen.

One thing that may be tricking me is that I sit close to the screen, like 3 feet away.  When I set back on the couch and look the image looks much more correct to me.  

EDIT: Problem Solved!

I went back to my original problem with this monitor.  The screen was too dark when I got it so I took the back off and turned up the screen setting. 

When I did this I used a Terminator 2 dvd with a THX calibration program.

But, I didn't know that the S-video input would be much brighter than the RGB.

So THIS TIME I used my computer and Nokia monitor test to calibrate.  I used the black and white contrast bars option to tune it.

I turned up the brightness til retrace lines appeared in the image, then back the knob back off my just a couple of millimeters or so.  It was extremely sensitive. 

I did all this while making sure that my contrast and brightness were at their default settings. 

Once I had achieve the most brightness I could achieve without lines appearing, I attempted to adjust the image.  All of a sudden dingy white became white white!

I exited out to the desktop and it looked like a desktop is supposed to look.  I fired up Super Street Fighter (the game I know most what it should look like) and it looked better than I've ever seen it.

This monitor has color and contrast the equal of my little PVM.

Now if I could just get that blue convergence right.....

[Ummon]

S-vid obviously amps some part of the signal. Every time I've seen it, while the colors are pretty vibrant, blacks are misty. I think yer just messin with it too much.