If you are in the US and do any sort of retro gaming on a consumer television set, you probably lament its lack of an RGB input. This is due to the fact that more RGB inputs were typically only found on professional monitors like Sony’s PVM series or European TVs.
This is unfortunate, as consumer TV's are cheap, plentiful, and often come in larger sizes which can make for a more immersive gaming experience, especially if you are into light gun based games.
If you are looking to turn your mediocre consumer display into something akin to a pro RGB gaming monitor, than you’re in luck. Most TV’s can be modified to unlock their RGB input. It may seem a daunting task at first, but with your TV’s service manual and the right tools a mod like this is actually quite simple.
Varying results can be achieved depending on the TV’s age, model, and overall condition. The obvious choice for this mod is Sony’s Trinitron series, namely the FV310 model, as it produces a picture that is roughly on par with a low end PVM monitor, albeit without the highly accurate color reproduction. This guide will be using the FV310 as an example, but it can be applied to certain other TV sets as well.
Modding a consumer TV for RGB is actually quite simple, depending on what you want to accomplish. The method detailed in this guide is the one I prefer, as it eliminates a lot of potential problems that can occur when you don’t isolate the circuit.
Note: The process to mod a specific TV will vary slightly depending on the specific type of RGB mod you plan to utilize and whether or not you have a service manual handy. This guide will detail a Jungle IC hack, and assumes you have located the TV’s Jungle chip and know its pinouts.
Using The On Screen Display As An RGB Input
Although TV's in the US did not have RGB inputs, that doesn’t mean the technology was any different – all CRT TV’s use the same red, green, and blue electron guns to generate an image. This is most obvious when you look at a TV’s on screen display (OSD for short) as it is clearly of very high quality when compared to the composite picture it is usually overlaid upon.
What this means is that there actually is an RGB input in most TV’s with an OSD, but it is only exclusively used for the OSD. Luckily, there is a way for us hijack this input and use it to display something more interesting than a simple menu.
In order for us to get our RGB picture, we will need to find a the chip that controls this OSD and pull the signals from it.
JUNGLE IC
Most modern TV’s made after the early 80’s are more like simple computers in that they have a micro processer that enables control of the various functions in the TV set. For whatever reason, these are referred to as the “Jungle IC” in various TV service manuals. If you are looking to hijack an OSD signal, you will probably need a service manual for your TV.
You will want to look for the pin out of the Jungle IC, which will display which pins connect to what and perform which functions. Every service manual is different, you will want to keep an eye out for something that looks like OSD_R, OSD_G, and OSD_B. sometimes they will not be labeled at all, but often you can extrapolate the OSD RGB pins as they are usually close together and can be traced out via their circuit.
These RGB pins control the TV’s OSD input. When you turn the menu on, the tv inputs the signal through these pins. Note that it is important to make sure it is an INPUT, not an output. In the case of this set, the inputs we will need to use are labeled R-In, G-IN, & B-IN or pins 41, 42, & 43 respectively.
Lastly, we also need to find the blanking pin. This pin tells the TV to send the RGB signal over the entire screen. Without it, we would just have the small text of the menu to play our game through. This pin is usually identified as Y. In this case it is labeled as "YS2/YM" on pin 40.. Every TV is different and you may have to trace out the circuit if the labeling is ambiguous.
CRT Disassembly
To start, we will have to remove the back of the TV. As CRT's are front heavy, it’s best to do this on a large surface area in case of any mishaps. This is especially true if you have a larger tube.
Most consumer CRT TV’s have about 10-12 screws that secure the back of the plastic panel to the front of the chassis. After removing these you can usually slide the panel right off. The KV27FV310 seen here has about 10. The screws near the inputs on this TV do not need to be to be removed until unless you want to mount your SCART port there.
The first and most important thing you should do when working with any CRT (you did remember to unplug it, right?) discharge the tube. Most modern CRTs will discharge the tube automatically during their power down sequence. You can do this with a discharging probe or a screwdriver and an alligator clip. Attach one end to a grounded portion in the TV or the grounding strap. Slide the screwdriver under the rubber anode cap until it hits metal- you should hear a lot snap as the tube discharges. Most of the time there won’t be any charge in the tube as it is supposed to discharge when you power down the TV. Its best to always perform this step to be on the safe side though.
You should also remove the anode cap. It is wise to avoid touching the underside with the metal clip, as well as the flyblack transformer that it is attached to.
Note: It is possible for a CRT to build up a charge even if it has been off and unplugged for a long time due to the Earth’s magnetic field. I’ve personally never seen this happen, but I always discharge the tube regardless of whether the TV has been unplugged or not.
This next part can be tricky. We will be removing the mainboard that holds the Jungle IC. The FV310 has a lot of extra circuitry as it was a premium TV set. This makes it more akin to a pro monitor in its interior. Which means wires. A lot of wires. If you don’t have a good memory your best bet is record yourself or take lot of pictures to make sure you can remember where each wire goes.
When you’re done disconnecting all of the wires you should remove the mainboard. On most Sony TV’s and the FV310 there is a small clip on the left hand side that can simply be pushed outward, allowing the mainboard to slide out. Fortunately for this set, there are no screws to fiddle with on the interior.
Next we will be desoldering the 3 RGB pins as well as the blanking, (usually labeled as "Y, OSD_Y, etc) on the Jungle IC. As always, I recommend the use of a good desoldering tool, but a braid or pump can be just as effective here.
Attach your 4 wires to the RGB & blanking pins and wire them into the SCART head, assuming you are opting to go with a SCART attachment for you RGB connector that is. If you don’t know the pinout of a SCART head here is a quick diagram.
RGB Signal
Remember, for this to work we will need a properly attenuated RGB video signal. The good news is that most Jungle I/Cs have an integrated video clamp circuit, so all that is really required is lift the pins out of circuit and terminate with a few caps/resistors to match the impedence to ground, which will attenuate the RGB signal to 0.7vPP.
Without going into too much detail, basically this means running 1 75Ω resistor/0.1uF capacitor tied to ground on each of the RGB lines. For the grounds, I usually just wire them directly into the pins on the SCART side and bridge the common ground in the SCART header, as it will be grounded when you connect your console source. You can pull ground from someplace else on the mainboard of the TV and wire it into pin 21. I find this method keeps things a bit cleaner since you can have everything inside the SCART header. Be sure to wire the OSD blanking pin into pin 16 of the SCART header as well, so when you switch your console on it will send 5V to the blanking pin, which will allow the picture to fill the entire screen.
If you are using a SCART header as your RGB input, be sure to wire the red, green, and blue lines on to the ends of the 3 capacitors.
In the above photo red green (purple wire in my case, as i was out of green wire!) & blue are wired to capacitors attached to pins 15, 11, and 7. Resistors are attached to each of these lines and then to the corresponding ground pins - 13, 9, & 5. The other photo has video sync/blanking on pins 20 & 16. Audio left & right are on pins 2, and 6. The black wires are all grounds.
Don’t forget to wire in the left/right audio channels and an audio ground as well if you intend to use the low quality TV speakers. In this case, the FV310 is one of the rare consumer TVs that actually has very decent sound & sub-woofer that produces relatively clear and resonant bass. It also has an audio pass through, so there is really no reason not to wire it up in this instance. One thing to be aware of is that some TV’s have a mechanical switch inside of them that will bridge the L/R audio channels into dual mono mode when there is no RCA plug inserted into the right audio jack. To get around this you can desolder the jack and remove the switch, but I find its easier to just plug a bare RCA cable into the right audio jack.
As for the sync signal, I recommend you use the Luma pin from the S-video connector and not one of the composite inputs. The reason for this is that composite is typically run through a lot of filtering, which can cause the image to be biased too far in one direction resulting a part of the picture being cut off. If you don’t have an S-video input than you will have to use composite, but many TV’s have a service menu that will allow for the composite input to be adjusted to compensate for any offset.
Mounting The Input
You will want to decide where to put your RGB input. As SCART is a big, bulky standard, some people prefer to mount the input on the side of the TV. This also has the benefit of allowing you to take the case off without pulling out your RGB mod. Personally, I think this looks tacky and I don’t like having wires anywhere but behind the TV.
The other option is to try and squeeze it in on the back of the input area. I like to mount my SCART input here when I do an FV310 mod. There is just enough room for it to fit.
Dremeling the case can be a headache and hard to get right. I recommend you practice on something else first otherwise you will wind up with an overlay large hole. I generally just trace an outline and then cut a small hole, and file the rest to make it fit.
Other Mods
Installing a switch
Although this is a successfully completed RGB mod, we had to sacrifice our OSD to do it. This can cause a problem when you want to make any changes & adjust the picture. To mitigate this its possible to install a switch that will allow you to view the OSD again, which will make it much easier to make adjustments to the RGB picture. This can get pretty complicated and it is still possible to see the OSD on most TVs even with the pins lifted as there will be a black outline that you can work from.
Check out the shmups RGB mod thread for more information about this particular mod.
Feeding RGB into the neck board directly
This method does not involve the Jungle IC and instead feeds straight RGB into the electron guns. This method has a few downsides to it. The major drawback is that the signal will be incorrect, as the neck board expects very specific voltages. You will likely have to do some adjusting with your resistor and capacitor values to achieve a decent looking picture. I dont reccoment this method although i may be slightly easier than the above method as you dont have to lift any pins on the IC. This method is generally the only option if the TVs Jungle IC does not run the OSD in RGB. Sadly, many newer TVs have a YUV based OSD.
Conclusion
Although it doesn't quite have the same contrast as a high end PVM/BVM, the FV310 produces a crisp & very sharp RGB picture due to Sonys aperture grille technology.
