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Author Topic: R G B and sync leads?  (Read 2123 times)

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R G B and sync leads?
« on: August 07, 2002, 01:48:44 pm »
Reading up on an artice from AC, they mention,

To connect to an arcade monitor, you need a video board that has tv output.  You do *NOT* use the composite or svideo out.  You can however tap the rgb and sync from the VGA connector (you will need a manual for your video board obviously).  You'll tap the red, green, blue, and sync pins of the VGA out, and match them to the appropriate pins of the monitor.  For sync, just connect the composite sync to the horizontal sync of the VGA connector.  

My question is: Is this only for arcade monitors, or is this applicable to televisions also? Is the only option for televisions just to use the external consumer inputs or could I try and find these 'inputs' and syncs on my TV? Am I talking apples and oranges here?


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Re:R G B and sync leads?
« Reply #1 on: August 07, 2002, 02:54:25 pm »
Buzz --

In the United States we dont have the luxury of TV's with RGB analog inputs.  The closest thing we have is Component video which is a mathematical combination of RGB in a different way giving us a CyCrCb inputs.  But connecting RGB to them wont give you a picture (or one that's usable) without high priced converters.

If you live in Europe, most TV's come with what are called SCART connectors. Basically 20+ pin connectors that have discrete RGB inputs among other things.

So, in the US, unless you're moderately skilled, you're limited to the "outside of plastic shell" consumer inputs the manufacturers decide to give you on your TV.  Of course this means really crappy picture quality compared to an arcade monitor.

If you search this forum, and a little on google groups (usenet archive), there is ability to either hack into a TV or replace the electronics of your TV (keeping your tube) and sending in RGB analog video like an arcade monitor.

But in either case you must know all the safety issues surrounding working with televisions opened up and swapping tubes, and isolation transformers (to keep from blowing up your equipment or killing yourself)

And if you do go the hack route, every TV likely has a different way of hacking into the board, and require little to a lot of extra components to "adjust" the signal correctly. (e.g. many arcade boards put out 2-4 volts, where most computer monitors expect .75-1 volt, so your arcade board might overdrive the TV if you just "directly" hack it without extra components)  Again, not a project for someone who doesn't know how to safely work with 22,000 Volt picture tubes and electronic components.


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Re:R G B and sync leads?
« Reply #2 on: August 07, 2002, 03:00:35 pm »
And yes, I have personally hacked an old 13" Maganavox made Color Composite monitor/TV made for using on VCR's or old Commodore 64 equipment.  In that case the monitor already had an isolation transformer built into it (unlike TV sets) and it was very easy to find the digital to analog converter and cut it out of the circuit cutting one +5 volt wire, and then wiring in an external connector to it's RGB outputs, and then running the sync line into the normal H+V sync input. I needed to add 4 potentiometers to drop the signal strength correctly (ripped out of old VCR boards).  I posted my results on google back in June if you search for "Commodore 1902A Analog RGB" you will find the post.

But even I havn't attempted to hack a TV set yet. I've wanted to, but depending on the set, it's hard to even find where it gets converted. Most after 1986 have large IC chips that do the work. Older ones had numerous components with even test points to feed it in to test them in the shop when repaired. (like old RCA ones). Again, hacking them ain't for the faint of heart or un-knowledgeable. You can hurt/kill yourself or ruin tons of electronic equipment if you dont do it right.  Never open up a TV set unless you know what you're doing.


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Re:R G B and sync leads?
« Reply #3 on: August 07, 2002, 03:15:19 pm »
Hmmm... I have an old JVC AV-2090 20" TV with RGBI input that used to work with the commodore 128. Would this work well for an arcade cabinet?



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Re:R G B and sync leads?
« Reply #4 on: August 07, 2002, 07:16:36 pm »

Your TV would likely not work without hacking, unless it has an SCART connector (e.g. if it was a high end set sold to Audio/Video production companies it might have it.. I've seen the 19" JVC version of the 13" Commodore 1702 monitor at thrift stores before, dontated by local TV stations..they had SCART connectors on them).

RGBI is "digital" (aka "Intensity" bit) RGB, where RGBA is "analog" RGB.

Basically all TV/Monitor tubes take Analog signals, and that's what Arcade boards put out--NOT analog. However, some monitors were built with a Digital interface to the outside, and converts it to analog inside, but not offering analog to the outside.

This is what my Commodore 1902A model by magnavox was. It had a daughter board that converted Digital RGB to Analog RGB.  Simply take the board out of circuit by cutting traces to it, then feed in the analog where it output the converted.

Arcade game boards all put out (to the best of my knowledge) Analog RGB.

Digital RGB works as follows:
Each wire (R,G,B) specify either a 0 volt or 1 volt signal. 0 being off, 1 being on.  Therefore with Digital RGB that's 2^3 = 8 discrete colors.  However, a 4th line called "Intensity" (I) was added. When it is 0 the color is at half brightness, when 1, it is at full brightness.  This means 2^4 = 16 discrete colors.  Thats why computers like the Commodore 64 and original IBM CGA graphics were limited to 16 colors.

Analog RGB works by an "unlimited" (theoretically) variation of voltage.  Computers work in the 0-1 volt range (Commodore Amiga, VGA, etc..) Arcade boards worked in the 2-4 volt range.

The higher the voltage, the brighter the color. But totally variable. Therefore it's no longer digital, and theoretically unlimited (or at least 24 million+ colors as the human eye can discern)

Therefore to connect an arcade board (or special VGA adaptors that can sync down to 15.75 KHz horizontal for TV use) you need to get the analog signal out into the analog signal in of the monitor. And if it's not an authentic arcade monitor supporting the higher voltage range, then you'll need to reduce the voltage to meet what the monitor wants, as I previously aluded to.

Again, hacking into TV's/Monitors is a very interesting project, but please don't do so unless you know what you're doing. Don't entirely trust what someone else writes on the internet. Do your research. Understand voltages, resistance, capacitance, isolation, etc... before you start such a task.

Oddly enough though, of course, your arcade board AND computer initially work with video VIA digital RGB, either 4 bit (16 color) 8 bit, 24 bit (24 million colors) or 32 bits.  Just before what your game draws leaves the board, it changes the digital signals into analog ones to feed to the monitor.

PS: You CAN send analog RGB output into some digital RGB inputs, but you'll be left with only 8 colors, and likely washed out or too dark too.  So unless your game only draws in 8 colors or less (not very many!), you'll need Analog RGB inputs.