RGB out of this? - I think I found something

[Ummon]

I was given a Mitsubishi CM-2501 presentation monitor. It has composite input, and also a strange rectangular jack that sticks out below the composite. It has eight holes, numbered, and it says RGB next to it. This is what the previous owner said about it:

The RGB input you find isn't a computer RGB input - it's studio video RGB taken from a camera.  The signals are all supposed to be 1v P-P driven into 75 ohms. Computer RGB (for the IBM CGA displays) from the late 80's uses TTL levels (0-5 V) I think.<


Is it possible to somehow send VGA to this?

[StephenH]

Computer RGB/VGA is 0-1V.   You probably need some kind of breakout cable or the pinout for the RGB  connector.   You also need to find out if this monitor is 15Khz, 25Khz, 31Khz.   If it is 15Khz, you probably will need an ArcadeVGA or Soft15Khz.   

[Silver]

It will be 15Khz if it's designed for use in studios.

8 pins will probably be:

R (signal+ground) G (signal+ground) B (signal+ground), Horizontal sync and Vertical sync. = 8 wires.

So you can either try all combinations all search for a pinout.

I'd be wary of hooking up a 31Khz signal to such an old monitor though, so make sure you are outputting 15Khz.

[Ummon]

It will be 15Khz if it's designed for use in studios.

8 pins will probably be:

R (signal+ground) G (signal+ground) B (signal+ground), Horizontal sync and Vertical sync. = 8 wires.

So you can either try all combinations all search for a pinout.

I'd be wary of hooking up a 31Khz signal to such an old monitor though, so make sure you are outputting 15Khz.

Yes, it's 15khz, etc. What I'm wondering is, since the signal voltages are different, am I going to blow it up?...do I somehow need to step them down?...etc

As for the pinout, I'm still working on that, though couldn't I just tell with a meter? What values would I be looking for in this case that would distinguish the components?

[MonMotha]

The signal levels are not different.  What the guy told you was true...20+ years ago.  Since the advent of "VGA" in the late 80s, PCs have output 0.7Vpp (1Vpp if sync is embedded on the green line, -0.3V for sync) analog video to be teminated into 75 ohms with separate or composite (usually separate, but often configurable) sync.  The pinout of the HD15 is even based on a somewhat de-facto standard from the broadcast world in order to be compatible.

If it really is designed to accept analog video + TTL sync, then chances are the video inputs would read ~75ohms from signal input to ground while the sync inputs would be relatively high impedance.  If you post a picture, somebody might be able to identify the connector for you, and there may be a known/standard pinout for it.

[Ummon]

Here are some pictures of the rgb port.

[Ummon]

I was able to get a decent picture of the backside of the input.  Behind the front set, from top-right to bottom left, it goes blue, yellow, red. The last pin - behind the fat yellow - is connected like so: a small wire, it goes laterally from black to fat yellow to last pin, and then off and around to the 'coupling' on right. Is this layout recognizable?

[Zebidee]

Try having a look at this pinout for connecting to a Roland monitor. The connector looks like yours:

http://myweb.tiscali.co.uk/clouzeau/s760/images/rgb25n.gif
http://myweb.tiscali.co.uk/clouzeau/s760/monitor.htm

Anyway, it seems to match what you were describing, with the black & fat-yellow wires connecting to the coupling + pin 1(?), seems to match this diagram.

Give it a go and let us know!  I've stared at these before and been bewildered.  Would love to know more 

[SavannahLion]

Holy smokes, that is the exact RGB pinout connector I have on my Sears SR3000. I've been meaning to tackle the pinout but never got around to it.

Is the voltage on your typical JAMMA board compatible with this kind of monitor? I recall reading the specifics on video signal from arcade boards, but now I can't seem to locate it.

[Zebidee]

SL, you'd be better using a PC output to test with.  You are looking to get TTL levels on the RGB signals, up to about 1v or so, and PC video cards output at these levels.

To use a JAMMA PCB, you'll need to put some resistors on the R-G-B input signal lines - 75-100 ohms should do the trick.  The sync levels are probably OK but test them - should be around 3.5v, give or take.  If the sync comes out at 5v, then try a 48-75 ohm resistor on that line as well.

Don't forget your digital multimeter!

[Ummon]

Try having a look at this pinout for connecting to a Roland monitor. The connector looks like yours:

http://myweb.tiscali.co.uk/clouzeau/s760/images/rgb25n.gif
http://myweb.tiscali.co.uk/clouzeau/s760/monitor.htm

Anyway, it seems to match what you were describing, with the black & fat-yellow wires connecting to the coupling + pin 1(?), seems to match this diagram.

Give it a go and let us know!  I've stared at these before and been bewildered.  Would love to know more 

Hmmm. Plug is the same, but the wiring's way different. I might've found the correct manual. I just haven't decided whether I want to risk the money.

[Ummon]

Okay. I recently came across some Sony PVM-2530 monitors and they have this same connector far as I can tell. It is for a VTR. I'm googling on this but nothing schematic-wise yet. Anybody know anything about this format?...any standards, etc?


<later>

Hmmm....I found this (pictured below) in the manual. Does this mean it's not an improvement in video quality vs using the actual composite input?...or does it mean they're the same?

[Jack Burton]

That same type of connector can be for both VTR and RGB.  If it is for the VTR it is actually composite video in and out combined.

[Zebidee]

Okay. I recently came across some Sony PVM-2530 monitors ...

For those monitors, you'll need to hack a cable to connect from VGA to 25-pin D-sub.

Here there is a manual for the Sony PVM2530.  At the end there is a pinout for your 25 pin D-sub, and it shows that you can input an RGB signal through that.  Mind you, this is theoretical (ie I've never done it before).

I believe that you would need to hack your VGA -> 25 pin D-sub cable so that:

VGA pins 13 & 14 (sync) -> 3
VGA pin 3 (Blue) -> 4
VGA pin 2 (Green) -> 5
VGA pin 1 (Red) -> 6
And all VGA grounds connected to one of 15-24.

I think that you may also need to connect 5v to pin 10 in order to tell the monitor that it should expect RGB input.  Try connecting a bridging wire from pin 3 to pin 10 first, because this sync voltage may be sufficient.  Otherwise you'll need to bring 5v in from the PC internal power supply via a molex connector.  Furthermore, you might also need to ground pin 9 to 15-24 in order to tell the monitor that it is getting digital input, rather than sync-on-green.

Hope this helps.

[Ummon]

That same type of connector can be for both VTR and RGB.  If it is for the VTR it is actually composite video in and out combined.

On the Sonys yeah that's what I thought. On this Mitsubishi though it says RGB so maybe it is. Hmmm.

@ Zeb: not sure if you were just confirming my question on the Sony d-sub 25?

[Zebidee]

@ Zeb: not sure if you were just confirming my question on the Sony d-sub 25?

Yes, I am confirming your question.  However, I also thought it worthwhile to mention that I think you will need to send a switching signal to pin 10, and ground pin 9.  I'm not sure of your level of expertise, but other people read this forum too, so I figure it is worthwhile providing extra detail.  Forgive me if that proves unnecessary in your case - I'm not trying to tell you how to suck eggs.

[Ummon]

That's cool. I just wanted to be sure what you were telling me. Thanks.

Further on that, if the d-sub 25 is for computer output, why is it so different than d-sub 15?

[Zebidee]

Further on that, if the d-sub 25 is for computer output, why is it so different than d-sub 15?

"D-sub 15" is really just another name for the VGA output header from your PC - because it is tapered at one side, making a shape like a D.  The 15 refers to the number of pins.  Likewise, the "D-sub 25" header on your monitor has 25 pins.

Of course, the monitor is CGA and will only properly display video signals output at 15.7khz, so even if you have a working cable you will have to use an ArcadeVGA card or something like Soft15khz to get the right video output from your PC.  If not, you should still get a picture, but it will be doubled, with two long, vertical screens (if you are lucky - or perhaps nothing at all).

Where the monitor's input (and its manual) refer to "computer", this means a computer set up to display 15.7khz on a CGA monitor.  For example, this might include a Commodore 64!  It doesn't mean that it auto-magically displays VGA output from a standard, modern PC.  You will still need to make sure that your PC outputs the right video signal.

Again, sorry if you already understand this.

[Ummon]

I do understand the signal needed for the monitor. I didn't understand why I would have to do some things in the hacking of a cable, such those to tell the monitor it's getting digital output, that it's getting RGB, etc. I thought maybe I could just wire up the main leads (rgb, sync, ground) and that would be it. But no?

[Jack Burton]

I think all you have to do is wire it up and send a 15.75 khz signal at the correct resolution.  Don't think you have to worry about it being digital.

[Zebidee]

I do understand the signal needed for the monitor. I didn't understand why I would have to do some things in the hacking of a cable, such those to tell the monitor it's getting digital output, that it's getting RGB, etc. I thought maybe I could just wire up the main leads (rgb, sync, ground) and that would be it. But no?

Just read the manual.  According to the manual, by default your Sony monitor expects sync-on-green input (ie RGB with sync overlaid on the green signal) through that D-sub 25 head.  Where I mentioned signalling "digital" earlier, I was referring to the manual's own terminology, which means input from a "digital" computer as RGB+separate sync.  This terminology is confusing because the PC (your "digital" device) actually outputs analogue signals through the VGA video head.

Hook up your cable as a basic RGB+sync and see how it goes.  If it works without the signals, then sweet.  If it doesn't work or looks wrong, then try hooking 5v to pin 10 (or bridging the sync signal to it) and grounding pin 9.  I'm interested in what your results are, so let us know.

[Ummon]

Just read the manual.  According to the manual, by default your Sony monitor expects sync-on-green input (ie RGB with sync overlaid on the green signal) through that D-sub 25 head.  Where I mentioned signalling "digital" earlier, I was referring to the manual's own terminology, which means input from a "digital" computer as RGB+separate sync.  This terminology is confusing because the PC (your "digital" device) actually outputs analogue signals through the VGA video head.

Hook up your cable as a basic RGB+sync and see how it goes.  If it works without the signals, then sweet.  If it doesn't work or looks wrong, then try hooking 5v to pin 10 (or bridging the sync signal to it) and grounding pin 9.  I'm interested in what your results are, so let us know.

Groovy. Much clearer, thank you.