RGB Video Input Hack Is A Master Hack For CRT Televisions

What’s shown on the screen above is about half-way through the process of hacking RGB video into a CRT television that’s not supposed to have it. The lettering is acting a bit like a layer mask, showing bits of the Super Mario Bros. start screen which is being injected from an original Famicom. [Michael J. Moffitt] figured out that he could patch his signals into the multiplexer which is responsible for overlaying the TV’s menu system. Obviously you can’t get your Mario on with this view, but the next step was as simple as finding the blanking pin and tying it 5V. Brilliant.

This particular hack is worthy of recognition. But read through [Michael’s] write up and it’s obvious that he knows the driver circuitry beyond the realm of normal curiosity. If you ever get stuck while trying to do something custom, we’d recommend pinging him with your questions (sorry [Michael] but with great knowledge comes great responsibility).


20 thoughts on “RGB Video Input Hack Is A Master Hack For CRT Televisions

  1. I remember doing this for an arcade board back in the day with a bog standard TV. Did the same thing here as well by feeding the RGB into the OSD lines, fed the sync into the composite input and all was peachy. I didn’t add a switch though, so the OSD was permanently disabled. Ah those were the days.

  2. That looks quite awesome, I tried doing something similar a year or so ago. sadly, the OSD on the TV that I was using was TTL. I wanted to make a proper interface board to drive the neckboard’s transistors directly but never got around to it. at one point, I picked up a different CRT that I was going to try this out on, but it ended up in one of my kid’s rooms… maybe i should make a third attempt.

  3. Looks like a neat way to build a Mame cabinet using older TV sets. I’d imagine this wont work with every TV set with a micro that does an OSD. A nice addition to this would be a list of sets that could potentially have the desired chip set to accommodate the RGB conversion.

    1. Not only does SCART have RGB but it has a dedicated blanking pin for the exact purpose of overlays.
      In the days of CTR I played around with that plenty.
      So now I wonder if some models for non-SCART regions actually had the whole setup for it just not the connector. Although – most TV’s in the CRT age were very region specific and either PAL or NTSC and seldomly both, TV’s that could do both were a specialized item.

      1. I am in PAL region and the European TV’s on the market here had SCART and were usually multi-format: PAL/NTSC/Secam.

        The non-European sets were PAL only and never had SCART. Some however had provision for SCART on the input board but the socket itself and the co-responding components were not populated on the input or main boards.

        1. CRT type TV? I don’t think so, the early LCD types sure, but the old tech made it much too hard to cheaply do multiple systems, they preferred not to spend 20% of the cost on making it compatible with systems that were not available in the region of sale.

  4. Meanwhile, on this side of the planet, we were lucky to have S-Video in, let alone component in, on a CRT television. I’ve never seen a CRT TV with RGB (VGA) input. I’ve seen a very few 1080p wide/flat CRTs with HDMI. Really heavy!

      1. He’s trolling. No one could possibly misunderstand the purpose of giving credit so badly that they think you’re obligated to credit sources you neither referenced nor cited.

  5. It’s a nice hack but I honestly don’t see the point with component in on the tv. While technically not pure rgb, it’s pretty darn close. Also he neglects to mention that no Nintendo consoles, save the SNES, support rgb, thus why he’s using the famicom with a rgb mod.

    So he hacked the tv to support an output method that the console doesn’t support either and thus needs hacked. So you could hack up all your consoles…. or get a 30 dollar converter box.

    I don’t want anyone to misunderstand, the tv hack is impressive, I just hope the purpose wasn’t to get rgb for the NES because… well with the NES composite out is the best you’ll get without ruining it.

    Now most other game consoles, on the other hand, particularly sega, they support rgb natively… then again the tv has component in, so I’d probably still use an adaptor.

    rgb 2 component is merging signals, not splitting them and while adaptors that do it the other way around can introduce lag, it usually isn’t the case for something like this.

    1. Many digital systems have a RGB signal that is converted to CVBS with an extra chip (even in new devices released now), meaning you can easily intercept the signal. The advantage is obviously an incredible amount of improvement of the signal. Although on a CRT you are of course using an analog system of sorts; it still makes a big difference if done right.

      However on old consoles many people think the graphics look better when it’s not too digital I hear, seems the designers made if for CRT and when too digital, like with emulators, it becomes too blocky.

    2. Actually they have succeeded in getting rgb out out of a nes. It involves basically putting a board between the ppu and the bus. Theres a couple bits on the output of the ppu that tell you what palette index its currently rendering for the current pixel. Combine that with a trick to be able to differentiate between backround and sprites and you can get full rgb out.

      Other systems that nintendo made that support rgb are: Snes (with the right cable, they only took that out of the snes2), n64 (with a mod), gamecube (native if you have a pal gamecube, I think also the japanese cube), wii (possibly europe only), wiiu (again possibly europe only)

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