adding RGB to a CRT TV

Started by narke, July 16, 2010, 05:03:51 AM

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A friend and I have been working on adding RGB to a CRT tv with some degree of success however we have hit a dead end and were hoping that you guys could possibly help us out.  We have the data sheets of the tv chasis, osd chip and the video chip and are aware of  the dangerously high voltages in a crt and do discharge it prior to each attempt.  Up till now we've been going off of this guys guide for doing the mod    

Now here is what we have done:
1. Disconnected the OSD RGB output signal from going to the video chip inputs.  
2. At the video chips RGB inputs we inserted out RGB signal (sega genesis)
which at this point from our sega's RGB lines pass  to the video chip and junctions to a line that passes down through a 1k resistor to a ground.
so our RGB line looks something like this:    
                                                                                 sega------------------------video chip
                                                                                                            1k resistor
3.  We took the sync from the sega and passed it through a 2k resistor to the tvs composite video input (the addition of the resistor made the tv happy with the sync signal)

Finally, after all this we get a picture, full of RGB color goodness and a very sharp image.  The problem, however, is that everything that is suppose to be white is instead black.  Which is why I am here, we would definitely like to have white and black rather than just black.  So any helpfully suggestions or tips will be appreciated.  If you want the datasheets our tv chasis is a samsung K51A, the OSD is a zilog Z89331, and the video chip is a TDA8843

Edit:  We have added a 5v pull-up to our RGB inputs which came to some degree of success as we got white but no black ironically.  We are now testing with different resistors trying to dial it in just right.  New problems have emerged making our heads twist but on the upside we are getting closer to the goal.


Oooo.... I really like the RGB primer in the linked article.  It doesn't cover that there ARE SCART equivalent monitors in the US from Sony (PVM), Mitsubishi, and NEC...  So, "we" didn't exactly get the short end... just had to go high end!  :P  :D

Ah, RGB. The additive color model in which red, green and blue light are added together in order to reproduce every color that can be seen with the human eye. It is primarily used in electronic devices as a way to capture, store and display color information in graphics, pictures, video, etc.

RGB signaling provides the cleanest, purest form of analog video you can get from any video device. No wonder why computer monitors have used analog RGB since the introduction of VGA in 1987. But television is another story. Since the dawn of color TV, we've been stuck with lossy encoding methods in order to cram a full-color picture in the limited bandwidth of a monochrome transmission. It really bit us in the rear when the home computer and video game system revolution started in the late 70s, clever machines that used an inexpensive home television set as a video display. The lack of a direct RGB input on TV sets meant that the signal from the computer or game device had to be encoded in a suitable broadcast TV format, only to be decoded back to RGB inside the TV set, leading to considerable losses in picture quality.

The French did it right with the introduction of the SCART connector in the late 70s. It is a 21 pin connector that provides direct RGB signaling between a TV and external video devices, among other nice additions like automatic input switching and video overlays. It was made compulsory for new TV sets sold in France starting in 1980 and then it spread throughout Europe, becoming a de-facto standard for European TVs and video devices. Having a direct RGB input offers the highest possible video quality for your DVD player or video game console, and it also simplifies internal video circuits by a great margin. Almost every video game system sold in Europe comes with an RGB SCART cable as a pack-in or as an option, for a stunning monitor-quality video display.

We got the short end of the stick
Unfortunately, RGB SCART never took off outside of Europe. Here in America it is totally unheard of, which means that we've been stuck with crappy composite video and S-Video inputs in our TVs for decades, while Europe has enjoyed pure, glorious RGB since pretty much forever.

Just like European gamers got the short end of the stick with their video games having horizontal black bars, crappy frame rates and in the worst case a ~16.67% slowdown in music and gameplay speed, here we had to put up with prehistoric video connections and their horrid picture quality until Component video came and saved our eyes, but that was pretty late in the game, wasn't it? You can't have everything, they keep saying.

RGB is Godlike
Ever noticed how crisp and clear arcade games are in comparison to your home video games? That's because they use RGB signaling. It is the purest analog video signal you can get from the video output chip of your favorite game system directly into the electron guns of your TV set. Zero distortion, zero artifacts, blurriness and all those nasties introduced by NTSC/PAL color encoding, low quality TV decoding circuits and so on.

Don't take my word for it. Please, see it for yourself. Especially in consoles like the Sega Genesis which have a craptastic composite video out, the difference is like night and day.

I grew up playing the SNES through the RF modulator connection, and since I discovered the SCART connector I've been pissed off at the complete lack of a direct RGB input on American TVs.


Quote from: narke on July 16, 2010, 05:03:51 AM
A friend and I have been working on adding RGB to a CRT tv with some degree of success however we have hit a dead end and were hoping that you guys could possibly help us out.  We have the data sheets of the tv chasis, osd chip and the video chip and are aware of  the dangerously high voltages in a crt and do discharge it prior to each attempt.  Up till now we've been going off of this guys guide for doing the mod    

Whoever wrote that guide has the right general idea, but his actual implementation shows he is actually quite ignorant of the electrical propertied of video signals and how they are used in practice. You can be dead certain he hasn't tested his gorious new RGB input on anything other than his own Sega Genesis. Essentailly this TV can now accept RGB video arcade monitor style -- ie. every time a different device is connected the input he'll need to re-adjust those resistor values on the input.

Right, narke, your first step to acheiving your goal is to wipe everything you read from the article after the heading "Modifying the 3Y03 Chassis for Direct RGB Input" from your brain. You see, there are actually standards for these sorts of things.

1) A video input must be terminated with 75 ohm resistor.

2) After terminating, the video must have its DC level (black level) restored. This is most often done with a coupling capacitor and a video clamp circuit.

3) The standard signal level for a video signal is 0.7 Vpp (vots peak to peak) into a 75 ohm load. If the video signal contains sync information (which is 0.3 Vpp below the video) making a total of 1Vpp into 75 ohms.

There is nothing particularly mysterious or secret about this information. This is the kind of thing you'd best up in a techical book or paper, not the internet.

So you want to connect your Sega Genesis console to this Samsung TV. First thing to do is make sure your Genesis is actually generating a standard video signal. Check your RGB cable, in include some capacitors and resistors as shown in this diagram: If you, you'd better put them in place. Without a knowing what kind of signal you are dealing with, you will never acheive your goal.

Right, now you have a standard video signal, three of them actually, but I'll refer to one as they're all treated the same.  We know that the signal is 0.7 Vpp when we terminate it at 75 ohms. Take a look at the datasheet of the Jungle IC (TDA8843) and see under the heading "quick reference data" the parameter ViRGB happens to be 0.7 Vpp.  That's not to say that an RGB input to any given Jungle IC will absolutely be designed to accomidate 75 ohm standard video. Some are digital (TTL) inputs which can only be switched on or off, as this is all that is required by an OSD anyway. Sometimes a Jungle IC has both digital and analog RGB inputs - the digital ones being used for the OSD, the analog pins just sit there, bypassed to ground. Sometimes you find analog inputs which are spec'd at 1 Vpp or something else silly but it's fairly rare.

Back on track - BLACK LEVEL RESTORATION. That sounds complicated and a lot more involved that installing a termination resistor but that is very often not the case. If the analog RGB input is connected to the OSD you can check to see if there are any coupling capacitors in the signal path. If there are, then the jungle IC has an integrated video clamp, you need only supply the capacitors. The value is usually 10uF or 0.1uF, electrolytic and ceramic respectively. The value of the coupling capacitor is important and depends entirely on the characteristics of the jungle IC - older parts generally use larger coupling capacitors. If the analog RGB input is unused the capacitors are usually still present in the circuit, they just bypass the input to ground to prevent oscillation. Common sense should dictate the polarity of the coupling caps if they are of a polarised sort. If one end it tied to ground with a 75 ohm resistor and the other clamped at three volts or so it shouldn't be too perplexing to work it out.

Standard video input, check
video terminated, check
video coupled and clamped, check
Synchronisation is next. For this step connect the composite video signal output of the Genesis to the composite video input of the TV. Very easy. This is what the Europeans have been doing for decades and it works for them. Don't use the Genesis' composite sync output for anything, ever.

All that is left now is to enable the RGB input. There's usually a pin next to the other three video inputs called 'Ys' or 'FB' or 'RGB_INPUT_ENABLE_ACTIVE_HIGH' or similar. Often this is the equivalent of the RGB select pin on a SCART socket. It's the base of a transistor, applying a volt or so will bias it on and activate the RGB input. Sometimes it's just a digital TTL input.  Also take note of other components in the circuit before introducing any foreign voltage.

INTEGRATION with the rest of the TV, assuming you don't want to make it a dedicated RGB monitor. Can be acheived with the use of  mechanical switches. Toggle and rotary, and latching pushbutton switches are all good choices, keyswitches and knife switches are not. 

To summarise:

RGB input on the jungle IC of low end TVs are common.

Sometimes they are perfect match for standard video and designed to accomidate a SCART input (all LG and Samsung do - I'm fairly sure) and sometimes it's a useless digital video input. Sometimes it's a non-standard analog input. If it's this type it may not be worthwhile proceeding unless you're really keen, it may require actually learning about video signals to accomplish this.

Inputs are terminated with 75 ohm reisistor. Always.

Right after the resistor comes the coupling capacitor. Always.

Composite video is your synchronisation source.

Have a thorough look at the circuit and use rational thought to determine how the RGB input is activated.

It's easier to just find a cheap RGB monitor than worry about any of this non-sense.


this is pretty much the information I've been interested in for quite a long time now:)
another idea for further integration that I'm interested in is the use of the teletext function as rgb mode.
can you explain what you know about that? apparently there are some rgb lines somewhere between the teletext section and wherever it goes. I dont pretend to know the first thing about it but I read about it some time ago and would like to persue it one day if I have the information available.
are teletext and osd separate inputs?


Oh, we are aware it'd be easier to just get a cheap RGB monitor but we aren't about doing things the easy way.  My friend and I love to mod different things, we started out making out own RC cars then made them into cheap plastic battle bots, then progressed to modding computer cases, then before working on this we modded my sega genesis to have s-video.  So, this project is more of a learning experience and just for fun anyways, though having it work would be a great plus.   :P

Also, thanks for all the helpful information viletim, we'll use all the info the next time we work on it :)


So we disconnected the fast blank from the OSD to make sure when we put in a voltage source it only goes to the fast blank on the TDA.  After looking over the datasheet for the TDA it states "input voltage to blank the RGB
outputs to facilitate 'On Screen Display' signals being applied to the outputs" with a min of 4v.  So we took this as we should need at least 4v but we had a nice handy 5v source.  So we tried that and the result was a blank black screen.  Now when we don't have our fast blank tied to a 5v source we actually have a distinguishable picture, so we are confused on a couple things.  Does this mean we don't need to do anything with our fast blank? or Our we just using the fast blank wrong?



Read it again:
input voltage to blank the RGB
outputs to facilitate 'On Screen
Display' signals being applied to
the outputs

And applying said voltage makes the RGB outputs go blank! It hints that making the outputs blank might be useful if you want to apply an OSD signal to the output. You are not applying an OSD signal to the output, you mearly wanting to activate the RGB input. It's not an dedicated OSD input, you can use it for OSD of corse, but the datasheet refers to it as an RGB input .

What you really want to do is use the fast blanking pin to enable "data insertion". See S.3.2 and S.3.3. Basically, you need to apply 0.9-3.0v to this pin. Use a resistor divider from your 5v source, there's probably a resistor or two already in the circuit, account for it.

phreak97 ,

Often teletext and OSD share the same input on the jungle IC, they just don't come on at once. Though many TV sets which have built in teletext aren't the cheapest and may have a  significantly more complex circuit arangement that the typical micro + jungle.


First off we got it working!  So thank you for all your help viletim, you were a huge help and we definitely would of given up on it if it weren't for your help.  So thanks big time  ;D  Secondly, HOLY CRAP! RGB looks better than I ever thought a tv could look let alone a sega game.  Lastly, we have done one last thing to our beloved rgb tv, we have hooked it up to our arcade machine case mod so it's running off a computer via vga.  We did all the sync conversion thingy and installed soft 15khz. Mame games look amazing now, but we have one issue. We are running windows xp using an ATI x1300 video card at 640x480 but we lose some of the picture as it cuts off a bit of the bottom and a bit of the top of the picture on out tv.  Any ideas as to why we might be losing part of the picture like that?



On a typical TV, between five and ten percent of the picture is cut off (overscan). It's done because the average TV watcher never notices when some video information is missing but complains loudly if he sees the edge of the video on-screen.

You need to enter Service Mode to adjust it. The details should be in the service manual.


Well done, but let's see your pics! :)


I can't wait to see more pictures of this project!!! :P


Oh wow, didn't realize the interest in my project otherwise I would of been posting pics up earlier sorry about that.  Well, I got good news and bad news.  The good news is the tv is working great as a monitor for our xmen arcade machine nicknamed the "colossus" and we have pictures.  The bad news is the pictures aren't that great but hopefully I'll get better ones in the near future.

The tv chassis
all together

Another unfortunate event fell upon us.  After we got the modded tv back together we proceeded to move out the other tv still in the arcade but when we were trying to move it out the chassis got caught and snapped.  So we lost our second monitor, the tube still works and is in fact the same tube as the tv we just modded so if we can't find a replacement chassis at least we have a replacement tube lol.  If any of you guys know where we can get a new chassis or new tv/monitor for cheap let us know.  It HAS to be a 25" tv/monitor no other sizes fit.  Also, if you guys wanna see more picture just let me know I'll put up whatever you want.  We did just get some comparison pictures taken to show the difference from composite video to RGB video in use on the arcade. 


Hey, your project looks very nice!

I would like to see more pictures, currently I'm doing the same mod on my TV, may it could be fine if I can talk to you, may you can clarify me some doubts, well, I mean only if there is no problem, I don't want to be  a burden :)


I once had a Sears LXI tv that had plugs over the inputs that they didnt include.

it had a knockout cover for a scart connector. i never got to open it up to investigate if one could just be soldered in to it. that was years ago and the tvs gone now.

it would be nice to know wich other tvs were like this.


EDIT: figured it all out and did the work on another CRT.  Info here:

Hey all,
  sorry to bump an old thread but this one has TONS of useful info and it makes more sense than starting a new one methinks.

I am trying this mod on a Zenith 9" portable color TV I found today (made in 1993).  I am stuck here:
"If the analog RGB input is connected to the OSD you can check to see if there are any coupling capacitors in the signal path. If there are, then the jungle IC has an integrated video clamp, you need only supply the capacitors. The value is usually 10uF or 0.1uF, electrolytic and ceramic respectively."

There are no capacitors on the OSD RGB signal path, so the jungle IC has no clamp circuit I'm assuming?  What's the best way to build one?

Basically I get a since synced image with RGB but the colors are VERY primary RGB... no hues or tones or anything with gradation.  Assuming this has to do with clamping but I don't know for sure!

I followed everything else here very carefully.  The Jungle IC doesn't like having input caps to the OSD lines has just 2.6k ohms in line with the signals coming from the microcontroller (which is unknown).
The jungle IC is a TA8879N and the datasheet is over here:

What I did:
1) Pulled Ys to logic high (+5v) to put it in "black" background for OSD mode
2) used a voltage divider to knock down TTL Sync to 0.7v and input it via capacitor to pin 45 (Video In).  Sync looks perfect.
3) fed RGB to inputs 19, 20, and 28 via 2.6k ohms (on board).  I tried a bunch of different cap values looks like the inputs are DC coupled though so maybe I should just feed my game console RGB in without the 220uf and 75ohm parts?

I design PCBs for retro game systems :)