Modding a consumer TV to use RGB

Hello and welcome back to the 8-Bit Guy.

So, I’m sure you guys have seen this little TV in a lot of my episodes. I’ve been using it for years, and I’ve actually had this in my possession since 1997. I have a touch story to inform you that. I was actually working at AST computer. I worked in the tech support department and I actually have a lot of stories about that. And I actually hope to compile some of those little anecdotes for a video at some point. But, one among the items that really happened around 1997 is that AST was having some financial problems and that they were actually being bought out by Samsung. And, one among the items Samsung wanted to try to assist enlist the trust of all their newly acquired employees was to offer all of them a present.

And, we had the choice of receiving either a touch TV like this one, or a VCR, or a microwave oven. I actually opted for the TV. And it’s actually been a very fantastic little TV. Now, I would like to means that once I first received this, it had been 1997 and that I was 22 years old, and that i was living during a 1 bedroom apartment with my newly married bride. Well, at the time we didn’t have a lot of money and this actually became our bedroom TV and we actually watched TV on this. This is, this little 13 inch TV, it’s hard to imagine, this is actually what we watched TV on every evening for probably a couple of years. So, for the last 15 years or so, this has become essentially just a monitor for me. I don’t really use the TV part of it anymore.

In fact, I couldn’t even if I wanted to because analog TV doesn’t exist anymore. But, it makes a really good little composite monitor for hooking up to a Commodore, Nintendo, or Atari, or something like that. But, it's been delivered to my attention, repeatedly, over the last several months, that it's actually possible to mod consumer televisions like this to display an RGB signal. Specifically, an analog RGB signal. Now, why would I want to do that?

Most every computer made since the late 1980s has either supported some sort of RGB video signal, or simply hell for leather required an RGB monitor.

However, there are a spread of various standards. So the Amiga, for instance, used this 23-pin connector. The Apple IIgs used this 15-pin connector. IBM CGA and Tandy machines used a 9-pin connector. And of course, VGA is also a type of RGB signal as well. An RGB signal typically consists of 3 separate wires carrying the red, green, and blue signal. There is also typically a sync signal and a ground. Of course, any Color CRT television has to break the signal into RGB at some point because that is how it is delivered to the back of the cathode ray tube.

However, that's a high voltage signal at the rear, so ideally you ’d want to feed the RGB signal somewhere on the low-voltage part of the board. Let’s take this one apart and see what we can find.

OK, this is all pretty standard stuff for a TV from this era. First thing I’ll want to do is discharge the tube. This spring appears to be connected to DAG ground, so I’ll attach my alligator clip to that. I’ll attach the other end to a screwdriver.

And I’m not really expecting anything since this has been powered off for days and most TVs from this time have a discharge resistor. And yep, there’s nothing. I’ll go ahead and remove the suction cup. And now I just need to star unplugging things. I’ll start with the tube itself. And eventually, the board will come out. This thing is a bit dusty. I’ll go ahead and hit it with some compressed air.

OK, so watching this board, there are only two chips we'd like to specialize in. One is this micro controller. This chip drives the on-screen display, tunes channels, listens to the remote control, etc. This other chip here is what's commonly mentioned as a jungle chip. Almost every TV from this time period has one. This chip does most of the signal processing. One of the things the Jungle IC does is it takes in the composite video signal, and then decodes that into RGB and outputs it to the high voltage part of the TV.

However, it also accepts an immediate RGB signal from the micro controller for the onscreen display. But so as to understand when to modify thereto, there's another line called the blanking signal, which the micro controller will output when it wants to use the screen. So, what we'd like to try to is tap into this RGB signal here and take that to the rear of the TV. And then we need to locate 5V somewhere on the board and run that to a switch at the back of the TV that we can use to force the blanking signal whenever we want, so that the RGB signal will override everything.

There’s still one piece of the puzzle left. You still need to get sync from somewhere, well, we can use the regular composite input for that, because the jungle chip is designed to overlay the RGB on top of an existing signal, so it will still be looking for the sync signal from the composite input.

OK, so that’s the rough explanation of how this works. Now, I’m not going to go into great details about resistor values and stuff like that because every single TV is going to be a little bit different. In fact, analog electronics is not exactly my strong suit. I actually got tons of help from a man named Mark Cowan who searched the schematic diagram for my particular TV model and he actually helped me figure out which resistor values I needed for mine. Now, let’s get to molding. One of the first things I’m going to do is place a jumper wire across this resistor. I’ll be honest in that I don’t fully understand why I’m doing this, but I was told it would improve the picture quality.

This has something to do with the closed-captioning circuit where it dims the background around the text, and apparently we want to turn that feature off. And that should do it. Now, these 3 resistors here are on the red, green, and blue lines and their purpose is to lower the voltage coming from the micro controller to the correct input voltage for the jungle chip. Now, what we need to do, is add in another 3 resistors in series to these, like this, and then we would like to run our external lines in between them, like this. 

So, the way I’m going to do that, is I’m going to heat the legs up on one end of these resistors and pry them out. Then I’m going to straighten the leads on them. I’ll use some DE soldering braid to soak up the solder and open these holes back up. Then I’m going to take these 3 new resistors and put them in those same holes. Like this. And then I’ll solder in those resistors from behind. wires to the top of the triangle. I’m putting some heat shrink on just to make sure they never touch each other.

And there we go. There was also this unused connector port on the board, not sure what it was going to There was also this unused connector port on the board, unsure what it had been getting to be, but it has a ground available, so my 3 signal grounds are going to connect here. And there’s also a 5V signal in this same unused port, so I’ll connect to that for our little blanking switch. And I’ll just solder those in from the back. And then we need to connect a wire to the blanking pin on the micro controller. That’s where our 5 volts will go when the switch is turned on. It’s pin 25 on this chip, so I’ll just put some solder on the leg here, and then I’ll come back and just solder my wire directly to it. Like so. Believe it or not, that is all of the modifications that need to be done to the board itself. So, I ’ll plow ahead and reassemble everything for testing.

Now, I have this really long ribbon cable coming out of the TV. But, for the moment, I just want to find out if the TV is still working after all that I did to it. So, I’ll connect up the Apple IIgs from the composite port and hopefully the TV doesn’t blow up or anything. Well, here goes. Ok, no smoke or anything, so that’s a good sign. I did notice the onscreen display is a little dimmer than before, and I think that was to be expected with the mods that were made. But it is still plenty readable, so that’s fine. Let’s power on the Apple IIgs. And we have a picture, exactly like it should be.

OK, all good so far. Next, I want to do a quick and dirty hack here to test the RGB. So, I ’ve taken the ribbon cable and wired it straight to the present 15-pin connector. I’ve also just tied the blanking wires together. So, I’ll plug this into the back of the Apple IIgs. And let’s fire it up. To my amazement, it worked first try. And the signal is amazingly clear. on camera. But I’ll try to get some better close-up’s later. But for the moment, I’ll just run through these colors to make sure everything is correct, and it is. I will also set it to 80 columns for a quick test. Typically 80 columns on a television is unreadable.

However, it is very readable here. Again, I apologize for the moire pattern, but I ’ll get you some better footage later. So, what i want to try to now's find out where in here I can mount my connectors. I want to mount this switch and these 3 RCA jacks. The trouble is, if you reminisce here, there’s tons of stuff potentially within the way. I definitely don’t want to have the wires or back of the jacks bumping into these heat sinks, the fly back, or anything else. 

Now, there’s actually space on the side of the monitor, but I don’t think that would be particularly elegant. So, I think I’m going to put them up here. As always, I ’ll put down a bit of masking paper to mark my holes. That way if I mess up, I can just put a new piece of tape on there. I like all of my stuff to line up nicely, so I’ll start with a straight line. Then I’ll mark 4 spots that are 15 millimeters apart. Then I ’ll use a small drilling bit to mark a pilot hole on all. After that, I don’t need the tape anymore. Then I’ll drill the larger holes. And as you can see, perfect fit.

OK, so I’ve mounted the RCA jacks and toggle switch. Since I was not able to find any colored RCA jacks in time for this video, I’ll just add a little label here for that. And, this switch of course will enable or disable the RGB input. Now what’s left to do is solder wires to all of these things. And so skipping forward a bit, I’m just about finished with that. Now, this is an entirely separate ribbon cable. And so my plan is to put an IDC connector at the top of this ribbon beginning of the TV. The goal is that I want to still be able to remove the back cover of this TV without having to DE solder stuff. So I need a way to disconnect things. And so, I thought adding this connector would work well for that.

Unfortunately I ran into a problem on the other side. I thought I ordered a pack of male and feminine IDC connectors for ribbon cables. But the male connectors ended up being for PCB mounting, not for mounting on a ribbon. And I didn’t even notice that until just now. You see, I was thinking these would be just like the female versions where I could put the ribbon cable in. Since it could take several days to get those ordered, I’ve decided to take a shortcut for now.

I’m going to plop one of these little guys here on my quad hands. And then I just soldered all of the wires directly to these pins. And then, to form sure these don’t contact anything inside the TV, I ’ll coat everything with hot glue. Now, I did order the correct replacement part, which I’ll have in a few days. But for now, this should work. And so, as you'll see, I can now take the 2 halves of the TV and connect them together like this, before I reassemble everything. And now, I ’m getting to need 4 RCA jacks I can hook up with my Apple IIgs.

I ’m still getting to use this tiny prototyping connector for the instant because it is fast and easy. But ideally, at some point I will want to properly build a permanent cable for each of my systems. And here’s another annoyance. This cable set was originally advertised as being several feet long, and it’s actually really short. Originally I planned to cut it in half so I could use it on two systems. Now it looks like I’ll need to just cut these off at the end here. And so I’ve now wired these into the video connector. And on the opposite side I even have red, green, blue, and sync. So I can plow ahead and plug these in here. And the sync actually goes within the original composite port. Pity the cable didn’t have a yellow plug to match.

OK, let ’s do this again.

OK, on first try, I got nothing in the least.

But then I assumed, maybe I mounted the toggle the wrong way up. I’ve been known to do that. So, let’s flip it the other way. And try again. Yep, it works!

OK, so let’s try some games.

Wow, this looks really amazing. So I’ll flip the switch back to composite and check out the difference. It’s probably more noticeable on a close-up, so we’re still in composite, and look how much clearer it gets once I flip to RGB. So, let’s try another game. So again, we’re in RGB now, and here’s composite. Let’s zoom in a bit. Here’s composite. And now back to RGB. So, let’s try this Tandy Color Computer 3. It has a funky RGB port on the bottom, so I constructed this little cable for testing. I could probably make something more elegant later. So, let’s give it a try. And it works!

So, again let’s do some comparisons. I’ll switch it to composite mode and the text is much harder to read. And back to RGB. Let’s try a game. This looks great. I’ve never seen a Tandy Color Computer connected to RGB before, and it looks like a whole different computer. It’s really amazing.

Just to assist you visualize the difference, if you checked out an analog RGB signal through an oscilloscope, it might look something like this. By varying the voltages, almost an infinite number of colors are often created for any given

pixel. And that’s what we ’ve been working with up to the present point. But what would digital RGB look like?

Well, by its nature, digital is either on or off, a 1 or a zero. So it would look like this.

However, this setup would only allow a combination of these 8 colors to be produced. So, what they are doing during this case is add an additional pin into the combination called the intensity pin. By using this extra pin, it doubles the amount of colors, by creating brighter versions of each color, thus giving you a total color palette of 16 colors. And that is how CGA video works. So you need some extra circuits to convert a signal like this to analog Fortunately, I have this prototype device here from TexElec which will do just that. So I’ll just plug in my RGB cables. And let’s fire up the Tandy. And check it out! It works!

Now, there’s some overscan but I’ll deal with that in a minute. Now the Tandy also outputs a composite signal, which you are seeing now, so let’s put it back to RGB mode. Yeah, the difference is quite remarkable. So how do we get rid of the overscan. Well, this TV features a United States Secret Service menu that you simply can access. The service manual tells you the code to press on the remote, and here it is. There are a variety of adjustments I can make in here. And, as you can see, I can move the picture around and make it smaller. And, so, I’ll try Planet X3 in CGA mode. Looks good!

Next, I’ll try it in Tandy mode. And looks good there too!

Well, the Commodore 128 uses the same type of monitor as the Tandy, when using the 80-column display, so let’s try that. And there we go. And it’s definitely readable. So, let’s find something with some color. I mean, I guess I could have booted up GEOS, but it’s all black and white anyway. So this is great, I wish I had known about this years ago. 

I wanted to try one more thing before concluding this. I wanted to try a game console. I chose the Sega Genesis because it's a typical DIN socket on the rear, which was  easy to just poke some of the wires into for a quick test, rather than build an appropriate adapter. Now, the thing is, the Genesis has a pretty good composite output already. But RGB does gain some additional clarity.

For example, look at this yellow text here on this blue background. Now, when I switch to composite mode you’ll see like a black outline that isn’t supposed to be there, and that’s an artifact of composite video. And when I switch back to RGB mode, you can see it is gone. This is going to be more noticeable in areas of sharp contrast. For example, looking at the edge of this tree in composite mode you will see that same artifact, but when I switch to RGB it will be gone.

However, when looking at soft colored graphics like these, there isn’t a lot of noticeable difference. And although nearly every game console supports RGB video, I don’t think you’ll get as much improvement as you will with a computer, mostly because a computer is going to have a lot of text and sharp contrasts on the screen, where a game console won’t. So, personally, I’m really amazed by this mod, mostly because how easy it had been to try to.

And, you know, I ’m sure the people in Europe aren’t too terribly amazed because all of their TVs from that time period have the SCART connector on the back, which does essentially the same thing. Well, SCART connectors are nowhere to be found in North America, so this is far more useful to someone who lives in North America. Now, I’m sure a lot of people are going to be wondering why I didn’t put BNC connectors or a SCART connector or something like hat on the back of my TV. And, I certainly could have. 

I mostly just wanted to use the stuff that I had available at the time. But, if you opt to mod your TV you'll use whatever connectors you would like similarly. Myself, I’m just happy that I was able to essentially double the usefulness of this little TV without sacrificing any of its original functionality. And the other thing I wanted to tell you is that it should, in theory, be possible to run a VGA card on this TV.

And you might be thinking, well the frequency is wrong, but many VGA cards can be programmed to work at 15 kHz. And you can do that either in some Windows applications or there’s actually a DOS TSR that I’ve seen before that can actually change the frequency of your VGA card down to 15 khz. In which case, you could put that in your AUTOEXEC.BAT or whatever, and then you could run DOS games in VGA with this monitor, and it would probably look pretty good! Anyway, in order that about wraps it up for this, I hope you guys enjoyed it, and stick around

for the next episode and thanks for watching!

Apple iPhone 13