TV RGB Hack

[blackevilweredragon]

I believe this is what some people have been wanting for some time...  I have successfully hacked an NTSC Composite only TV into an RGB Monitor.

How?  Well, here's how some (if not most), CRT TVs do.  They seperate the colors into their RGB components and feed them to the CRT..  On my CRT, there was three wires labled R-Y, G-Y, and B-Y..  These were essentially just plain RGB..

So, got that, but how do you get the sync?  Well, since the H/V is still connected to the TVs own circuitry, just give the TV the Composite NTSC video, it will get the sync from that..  since we disconnected the RGB lines, it won't use the "video" part of the Composite feed..  Luckily this works since the sync is the same anyway..  You might get away giving Composite Video ports the Composite Sync line, but I don't recommend it, unless lawrence says it's safe..

Oh, and you WILL need to connect a 75Ohm resistor on each line, to the ground..  (NOT CRT GROUND!!!)  I did this as there would have been no impedence on the line, making the picture  VERY bright...

Here's pictures of the CRT closeup..  Anyone that knows the Genesis will say that's RGB..  Sorry, my digital camera kicked the bucket today, so all I have to offer is webcam shots..

[viletim]

Try an experement - put a capacitor in series with the video signals.

BTW, The way you get the sync information from the video signal is same way TVs with an RGB SCART input do it. Nothing wrong with that.

[blackevilweredragon]

Try an experement - put a capacitor in series with the video signals.

BTW, The way you get the sync information from the video signal is same way TVs with an RGB SCART input do it. Nothing wrong with that.

just tried it..  it seemed to have made the colors a little more vibrant..

what did it do?

[Qjimbo]

Do you think a similar thing is possible with say... a TV tuner card? I have a Theater 550, though considering most stuff seems to happen inside the one chip it's a bit unlikely. How would you go about determining what pins might be the RGB ones? You obviously had the advantage of them being labelled though =)

Anyway, nice hackery there!

[blackevilweredragon]

nope, not on a TV tuner card..  this only worked because a CRT is natively RGB, and the pins were right there..

I noticed on VGA monitors the RGB lines go right to the CRT neck circuit..

[nyder]

What about the borders?

Or is it basicly just a better TV picture?



Still, my big 1987 top of the line RCA TV would look a lot better if I could input stuff in rgb instead of composte & rf (cable connector, only the cable box is connected to that though).  No svid.  =(

Has some kicking speakers though, real nice bass.

But I guess if I wanted to take my TV apart, I'd fix the big apple monitor I have.

[blackevilweredragon]

What about the borders?

Or is it basicly just a better TV picture?



Still, my big 1987 top of the line RCA TV would look a lot better if I could input stuff in rgb instead of composte & rf (cable connector, only the cable box is connected to that though).  No svid.  =(

Has some kicking speakers though, real nice bass.

But I guess if I wanted to take my TV apart, I'd fix the big apple monitor I have.

the borders?  that's a part of the Genesis VDP, that's always there, even in the KEGA Fusion emulator, it's there...

RGB is the most crisp picture you can get..  So good, computer monitors use it..

[nyder]

What about the borders?

Or is it basicly just a better TV picture?



Still, my big 1987 top of the line RCA TV would look a lot better if I could input stuff in rgb instead of composte & rf (cable connector, only the cable box is connected to that though).  No svid.  =(

Has some kicking speakers though, real nice bass.

But I guess if I wanted to take my TV apart, I'd fix the big apple monitor I have.

the borders?  that's a part of the Genesis VDP, that's always there, even in the KEGA Fusion emulator, it's there...

RGB is the most crisp picture you can get..  So good, computer monitors use it..

Sorry, I should of said overscan, not borders.

I wasn't thinking of video games when I asked them, I was thinking of hooking up like an ST, or a C64.

the overscan would only matter with them, not the vid game consoles.


How do you connect your console to the tv?
How does normal TV look?


And just to clarify what you are doing, you modded your tv to just display RGB instead of the tv converting the signal to composite?

Can you take a picture of the mod you did, or describe what you did better?

You said:

How? Well, here's how some (if not most), CRT TVs do. They seperate the colors into their RGB components and feed them to the CRT.. On my CRT, there was three wires labled R-Y, G-Y, and B-Y.. These were essentially just plain RGB..

So, got that, but how do you get the sync? Well, since the H/V is still connected to the TVs own circuitry, just give the TV the Composite NTSC video, it will get the sync from that.. since we disconnected the RGB lines, it won't use the "video" part of the Composite feed.. Luckily this works since the sync is the same anyway.. You might get away giving Composite Video ports the Composite Sync line, but I don't recommend it, unless lawrence says it's safe..

The first paragraph you said"... there's 3 wires labeled R-Y..."
Then in the second paragraph you said"...since we disconnected the RGB lines..."

We did?

Can maybe you write it a bit more clearly and take some pictures or draw some diagrams?

Because why what you are saying isn't making much sence to me.  How does it display RGB if you disconnect the lines?

From what I see, you are saying you disconnected the rgb lines and are feeding it the composite signal.
So, instead of it getting composite then splitting it back to rgb, it's getting the composite and just dealing with that.

It's just how you are saying it isn't making sense to me.   You haven't mentioned how you get the RGB signals to the TV, and you talk about disconnecting the rgb lines.


I'm not challenging what you are saying, It's just by what you have said makes no sense to me.    So maybe can you explain it again, but a bit more clearly, so those of use that aren't there with you can understand what you did?

Because if the CRT did RGB natively, then the composite signal that comes in gets split into it's seperate signals, then those get feed into the tv.  Which would mean you just need to by pass the composite input and solder on plugs to the points where the various signals go.

I just can't understand it as your saying it.

[blackevilweredragon]

I did say things very clearly, you just don't know how the Genesis outputs video.

The Sega Genesis supports RGB output, but this TV doesn't take RGB input.  EVERY CRT picture tube only does RGB, as there's three R, G, and B guns.  Instead of using the TVs comb filter and tuner, I disconnected the RGB wires to the tube from the TVs Chasis, and connected the Genesis right to the tube.

That's not hard to understand at all.  If you don't understand it, that's your fault...  Sorry to be harsh, but you did to me (with no understanding at all)...

[kendrick]

What type of TV did you do this on, Dragon? I'm personally afraid of screwing around with picture tubes, but if the model you did this on is that easy to rewire then I'm going to go out and get myself a few dozen just for fun. :)

-KKC, who has given up on PC repair and is now deep into PC replacement.

[blackevilweredragon]

What type of TV did you do this on, Dragon? I'm personally afraid of screwing around with picture tubes, but if the model you did this on is that easy to rewire then I'm going to go out and get myself a few dozen just for fun.

-KKC, who has given up on PC repair and is now deep into PC replacement.

It was some old "SEARS" TV..  It says "LXI Series" on it...

[viletim]

blackevilweredragon,
The problem with this arangement is that you loose the convenience of a standard signal. Connect some other console, like a SNES, and your brightness and contrast will change. There is no way to adjust these - It's pure luck that a 75 ohm resistor in parallel with the Genesis' video outputs has arrived a signal level that works well with your particular TV.

Your TV uses the colour difference drive method which was quite popular in older TVs. There are four signals: R-Y, G-Y, B-Y, and Y. In this arrangement, the Y signal is added two the three colour difference signals at the final video output stage (usualy on the CRT neck board). In most cases I suspect it's ok to feed R, G, and B into R-Y, G-Y and B-Y as long as no signal gets into Y (and artificaly boosts the 'grey' video content).

I suggested the capacitor experiment just so you would see what it looks like to feed AC coupled video (most game consoles have (saturn) or require (genesis) a cap in the signal path to make the video 'standard') directly into the drive circuit. The result is not pretty - try it with video that changes from a dark scene to a bright one.

I've heard it's pretty common to modify a TV like this for use as an arcade machine monitor. Arcade PCBs always output DC coupled video and are usually pared with the same monitor for long periods of time - no need to worry about standards.  

[blackevilweredragon]

well the tubes neck board has CUT and DRIVE pots.. I'm sure if I move those evenly i can change brightness and contrast..

[Darklegion]

blackevilweredragon,
The problem with this arangement is that you loose the convenience of a standard signal. Connect some other console, like a SNES, and your brightness and contrast will change. There is no way to adjust these - It's pure luck that a 75 ohm resistor in parallel with the Genesis' video outputs has arrived a signal level that works well with your particular TV.

Your TV uses the colour difference drive method which was quite popular in older TVs. There are four signals: R-Y, G-Y, B-Y, and Y. In this arrangement, the Y signal is added two the three colour difference signals at the final video output stage (usualy on the CRT neck board). In most cases I suspect it's ok to feed R, G, and B into R-Y, G-Y and B-Y as long as no signal gets into Y (and artificaly boosts the 'grey' video content).

I suggested the capacitor experiment just so you would see what it looks like to feed AC coupled video (most game consoles have (saturn) or require (genesis) a cap in the signal path to make the video 'standard') directly into the drive circuit. The result is not pretty - try it with video that changes from a dark scene to a bright one.

I've heard it's pretty common to modify a TV like this for use as an arcade machine monitor. Arcade PCBs always output DC coupled video and are usually pared with the same monitor for long periods of time - no need to worry about standards.

Yeah, I had the same experience.I experimented with hacking TVs a few years ago and while it worked well with some consoles, it would have issues with others.The black/white scene changes were probably the most common problem with it becoming very bright when white scenes would come up.Also IIRC black levels were not correct in most cases either, with blacks being grey rather than black (although it was a long time ago, so my memory may be failing).
An alternative method that tends to work better, is to find the datasheet for the video IC that takes input from composite video, and find out if it will also take RGB signals.You can even use the OSD inputs if the IC doesn't have any external RGB inputs.

[blackevilweredragon]

blackevilweredragon,
The problem with this arangement is that you loose the convenience of a standard signal. Connect some other console, like a SNES, and your brightness and contrast will change. There is no way to adjust these - It's pure luck that a 75 ohm resistor in parallel with the Genesis' video outputs has arrived a signal level that works well with your particular TV.

Your TV uses the colour difference drive method which was quite popular in older TVs. There are four signals: R-Y, G-Y, B-Y, and Y. In this arrangement, the Y signal is added two the three colour difference signals at the final video output stage (usualy on the CRT neck board). In most cases I suspect it's ok to feed R, G, and B into R-Y, G-Y and B-Y as long as no signal gets into Y (and artificaly boosts the 'grey' video content).

I suggested the capacitor experiment just so you would see what it looks like to feed AC coupled video (most game consoles have (saturn) or require (genesis) a cap in the signal path to make the video 'standard') directly into the drive circuit. The result is not pretty - try it with video that changes from a dark scene to a bright one.

I've heard it's pretty common to modify a TV like this for use as an arcade machine monitor. Arcade PCBs always output DC coupled video and are usually pared with the same monitor for long periods of time - no need to worry about standards.

Yeah, I had the same experience.I experimented with hacking TVs a few years ago and while it worked well with some consoles, it would have issues with others.The black/white scene changes were probably the most common problem with it becoming very bright when white scenes would come up.Also IIRC black levels were not correct in most cases either, with blacks being grey rather than black (although it was a long time ago, so my memory may be failing).
An alternative method that tends to work better, is to find the datasheet for the video IC that takes input from composite video, and find out if it will also take RGB signals.You can even use the OSD inputs if the IC doesn't have any external RGB inputs.

i tried the Closed Caption RGB output for this originally, but experienced a weird glitch.  The picture would only show with CC enabled, and anything that was black colored from the Genesis, showed TV static..  So it seemed the TV had some form of overlay on it I think, and black was the magic color..

[antron]

I disconnected the RGB wires to the tube from the TVs Chasis, and connected the Genesis right to the tube.

so why do arcade monitors even have a chassis at all?  why not just the curcuit on the tube?

[blackevilweredragon]

I disconnected the RGB wires to the tube from the TVs Chasis, and connected the Genesis right to the tube.

so why do arcade monitors even have a chassis at all?  why not just the curcuit on the tube?

to have better control over the picture, and to take the sync, and turn it into something the yoke can use.

also it needs the flyback transformer, which is tied to the sync (i believe that is true)...  also the adjustments for picture geometry which is done either by POTs, OSD, or magnets..

All my VGA monitors, when cracked open, show the RGB wires going right to the neck of the tube...

[nyder]

Sorry black, I guess I missed you the part of you saying you hooked it straight to the tube.  

Actually, reading back, you never did say you connected the RGB lines to anything, but I guess everyone knew it.  I haven't taken the back off a tv to tinker around with it so i'm not sure exactly how they are connected up, though I know how they work.

I have an old color tv that was starting to die, wonder if I did your rgb hack it will make it display correctly again?  (rhetorical question).
Since it's been off for 6 months or more I might try it.

thanks for explaining the part again.  I just didn't want to piss you off like I was challenging you or anything.  Just wanted to figure out what I was missing.

=)

[antron]

You might get away giving Composite Video ports the Composite Sync line, but I don't recommend it, unless lawrence says it's safe..

So, does lawrence think it is safe?

What about mixing H and V syncs into the composite video?  What is an easy/safe way to do that?  This is starting to sound like the easiest way ever to build a MAME cab.

[blackevilweredragon]

You might get away giving Composite Video ports the Composite Sync line, but I don't recommend it, unless lawrence says it's safe..

So, does lawrence think it is safe?

What about mixing H and V syncs into the composite video?  What is an easy/safe way to do that?  This is starting to sound like the easiest way ever to build a MAME cab.

composite video contains composite sync, which is just H+V combined into one wire..  i don't know if the composite video jack can take a composite sync signal..  it might work, as we aren't using the video signal at all, and are just putting it directly into the CRT..

[ken_cinder]

Is this idea feasible? I am currently building an arcade cabinet, and I will have real hardware in it, as well as a PC for MAME in the future.

Can I feed the guns directly for my real hardware, and possibly add a switch to use those direct lines OR fed from the encoder for use with S-Video out on my PC video card?

I don't want to buy a true arcade monitor, and then have to figure out/spend money on a solution to use my PC with it later on. Though maybe that IS a better idea, with those ArcadeVGA cards?

[blackevilweredragon]

I would reccomend you do the more common mod, tapping the RGB lines of the character generator from the TV's computer/CC system..

Might be a far better picture than what I did...

[Hecubus]

Great discussion. About 10 years ago I also tried to tap into the OSD to feed RGB to the CRT.  I didn't have much luck and the girlfriend at the time was getting annoyed of have the living room TV in pieces so I gave up.  I think I may look into this again. Anyway...

I am surprised a word of caution has not been mentioned for the newbies poking around inside their TV's. I don't want to lecture anyone but be careful to stay away the flyback transformer and the big red (usually) wire with what looks like a suction cup that attaches to the CRT.  I'll cut'n paste a few words from http://www.repairfaq.org

If you need to probe, solder, or otherwise touch circuits with power off,
  discharge (across) large power supply filter capacitors with a 2 W or greater
  resistor of 100-500 ohms/V approximate value (e.g., for a 200 V capacitor,
  use a 20K-100K ohm resistor).  Monitor while discharging and/or verify that
  there is no residual charge with a suitable voltmeter.  In a TV or monitor,
  if you are removing the high voltage connection to the CRT (to replace the
  flyback transformer for example) first discharge the CRT contact (under the
  insulating cup at the end of the fat red wire).  Use a 1M-10M ohm 1W or
  greater wattage resistor on the end of an insulating stick or the probe
  of a high voltage meter.  Discharge to the metal frame which is connected
  to the outside of the CRT.

A good friend of mine, who introduced me to electronics, has a permanent scare on his finger, after a class mate thought it would be funny to sneak up behind him and scare him. He jumped, made contact, and really got the shock of his life. Pretty nasty. From my understanding the flyback can generate up to 35 KV. I have worked in TVs many times and have not had to discharge its load, but just be able to recognize the high voltage supply and keep away from it!

Happy poking and prodding.

[viletim]

Hecubus,
Well...there are warnings on the back of the TV...arn't they enough?

In the real world, in properly funtioning TV, the filter capacitors should all discharge through the surrounding circuitry within seconds of the power being removed. The picture tube can easily be discharged with a crocodile clip lead if necessary.

More practical warnings would be to double check that the power cord is unplugged when you expect it to be and that the TV is mounted securely so it won't fall off the bench and crush you from a sudden bump.

I've never heard of anybody being killed by a shock from the picture tube anode... I don't think there's enough stored energy to stop a human heart. The switching power supply on the other hand...

[phreak97]

yeah, i dont think it can kill you.. at least, im not dead, and i've had it go up one arm and down the other.. i've had a number of shocks from crts, and its definately worth discharging the EHT line (yeah, the big usually red wire with a suction cup looking connection to the tube). i use an alligator clip lead with one end clipped to the bare wire stretched around the outside of the tube, and the other end clipped to a flat screwdriver which i slide in under the rubber cup. this should be done repeatedly as the tube regains some charge after a short period of time. if not electrically dangerous, the shock will trigger your reflexes to likely drop whatever youre holding and pull your arms back really fast.. it's been known for people to accidently throw screwdrivers and such accross the room from the shock.. lol. so it can be dangerous in other ways and you shouldnt ignore it just cos it cant directly damage you. but trust me, after the first time, you wont ignore it

i dont have much to add to this discussion other than that lol. though i read about something like this a while back, whoever it was had used the teletext video line as an rgb input, because they didnt use teletext (who does?). which makes sense cos teletext has a pure black backing, and any of those overlay issues shouldnt apply. plus then you have an rgb button on your remote.. just press teletext. i dont know the sync details or compatability though.. maybe someone here can act on the idea however? i think i got a schematic for my tv somehow, so ill have a look at what's there, i wouldnt mind a mod like this, my tv went out of warrenty when the front buttons broke and i decided id rather fix it myself, so yay.