If you want high quality input from classic consoles to a modern flat screen TV, you need to use an HDMI converter like the X-RGB Mini Framemeister. This converter will take high quality RGB or Component video signals and convert them to HDMI-compatible 720p or 1080p with excellent results and minimal lag. I played with a Framemeister some months ago, and wrote up my impressions of the device here : http://nerdlypleasures.blogspot.com/2015/05/fun-with-framemeister.html Unfortunately, some classic consoles have difficulty displaying high quality video signals due to their lack of high quality video outputs. Some enterprising individuals have made mod boards that will directly convert the video to HDMI with less lag than a Framemeister, more features and more reliable results. Here are the projects that, as of the date of this writing, actually have been released in some form to the public.
NES - HiDef NES Mod & the AVS
The NES is one of the most important of the post-crash consoles and one of the few without a native RGB solution. There has been a NESRGB mod board released for two years now, which works wonders with a Framemeister. Before that people harvested 2C03 chips from Playchoice-10 PCBs and made do with the differences in the color palette, compatibility issues with color emphasis and sometimes video jailbars.
Kevtris' HiDefNES mod has already been mentioned in this blog, and it adds a whole host of features over the NESRGB + Framemeister solution. I lay them out in detail here : http://nerdlypleasures.blogspot.com/2015/07/analogue-nt-nes-as-luxury-retro-console.html
It is the board found in the Analogue Nt HDMI version and has been sold in pre-modded systems on ebay and on the http://www.game-tech.us/ website. The kit will be available for purchase so you can attempt to mod it yourself. However, it requires desoldering both the CPU and PPU without destroying either chip or the PCB, so it is not a beginner mod. Virtually all the compatibility issues with the HiDefNES mod and certain MMC5 games and the EverDrive N8 have been eliminated through a firmware update, so now is the time to consider taking the plunge.
The only obvious issue is that its FDS audio emulation is less than perfect. The mod will not work in an original Famicom, a Famicom Twin or an AV Famicom with laser-marked CPU and PPU chips.
The basic principle of how the HiDefNES obtains the color values of each background and sprite pixel is the same as used in the NESRGB. See here for my explanation : http://nerdlypleasures.blogspot.com/2015/06/nes-hardware-explained.html
There is now a 2600RGB board for the Atari 2600. The 2600RGB board uses similar principles to discover the colors of 2600 pixels as the NESRGB board does for NES pixels. Theoretically, it is quite possible for someone to develop an HDMI mod for the 2600.
bunnyboy, who runs the RetroUSB site, has displayed his AVS replica console at the 2015 Portland Retro Gaming Expo. His AVS has a 72-pin and a 60-pin connector for NES and Famicom games, and is designed as a front loader for the former and a top loader for the latter. It uses a completely new board and an FPGA chip to provide hardware emulation for the NES. It only outputs HDMI video and has separate power and reset buttons in the shape of NES front loader buttons. It has built in four NES controller ports that can be set to function as a NES Four Score or Famicom 4-player adapter. It also has a 15-pin Famicom expansion port for Famicom peripherals.
Because the console only supports HDMI output, it will not work with any Zapper or compatible Light Gun device and it will not work with the Famicom 3-D Glasses. The FPGA inside the console does not emulate any cartridge hardware or expansion audio. Expansion audio from Famicom cartridges is digitized and then mixed with the internal audio. However, because the AVS uses an FPGA, it can load updated firmware to fix any compatibility issues. Reports from the Portland Retro Gaming Expo were very positive, one person said the system ran Micro Machines correctly, which is a hard game to get right. bunnyboy is also designing wireless RF controller without lag to go with the console via an controller port adapter.
The console can only be powered through its USB port. The console has a scoreboard reporting function via the USB port, it will save high scores for certain known games and report them to NintendoAge. The idea is that you play a supported game, the high score is saved and then you plug in the system to your PC and it send the score to NintendoAge. The AVS only supports 720p while the HiDefNES can do either 720p or 1080p. The AVS is not for sale at the moment, but bunnyboy is aiming for a just under $200 price point. The best place for updates seems to be here : http://nintendoage.com/forum/messageview.cfm?catid=7&threadid=92557
N64 - Ultra HDMI
No N64 natively outputs RGB, but some early consoles can be modded with a simple amplifier board. Most consoles, however, have a video encoder chip that only outputs composite and s-video. These consoles require the N64RGB board. This board acts like a custom DAC, taking the digital signals from the N64 and turning them into analog RGB video. This will make it truly Framemeister worthy, although the s-video output from the N64 is pretty good compared to composite video. PAL N64s need a special cable to boost the S-Video signal from the console, NTSC N64s can use standard Nintendo or 3rd Party cables.
Today, if you want to bypass the Framemeister option, you can have an UltraHDMI board installed in your system. It works with NTSC and PAL framerates (up to 1080p for both) and not unlike the HiDefNES it comes with filters. The Ultra HDMI filters can simulate a CRT TV. Without the filters the lag is truly negligible, with them there is about a frame of lag. It supports all standard digital SD and HD resolutions, as shown here : http://ultrahdmi.retroactive.be/
The mod is very involved because you have to solder a flexible mylar-like ribbon cable to the finely spaced pins of the surface mounted graphics chip, the Reality Co-Processor (RCP). The RCP sends out 7-bit digital RGB values along with sync information. This allows for direct digital to digital conversion to the 8-bit RGB values HDMI supports without quality loss. The kit uses a mini-HDMI cable and only needs a small hole cut into the back of the N64. Because the mod is very tricky and not for the beginner, the board and kit is being sold only experienced mod kit installers. If you want your N64 modded with the Ultra HDMI, you need to send it to someone. This site is authorized to perform the mod : http://www.badassconsoles.com/ultrahdmi/
Game Boy - hdmyboy
In one sense, it is not too difficult to obtain a good quality HDMI image from a Gameboy. You use a Super Gameboy or a Super Gameboy 2 (for accurate speed) on a SNES that supports RGB and send the video and audio through a Framemeister. Alternatively, you can use a Game Boy Player and a Gamecube with the component video cables through the Framemeister, but that requires running custom software to make the Game Boy Player output at a true 240p speed.
Some time ago, there was a Kickstarter for a product called the hdmyboy. The campaign is archived here : https://www.kickstarter.com/projects/507669971/hdmyboy-a-full-hd-power-up-for-your-game-boy-class
This is a fully assembled kit that you insert between the two halves of a DMG-01 Game Boy. It adds half an inch or so to the height of the console when laid flat. It has an HDMI cable port and can support 720p or (preferred) 1080p.
Unlike the NES and N64 mods, this mod is easy to install. It requires no soldering. All you have to do is unscrew the shell, remove the ribbon cable that attaches the LCD PCB to the CPU PCB and insert that ribbon cable into the hdmyboy. The hdmyboy comes with a NES controller attached internally so you can control your Game Boy. It essentially becomes a consolized Game Boy at this point.
The Game Boy's LCD can only support four shades of one color, its video signal is fundamentally 2-bit digital monochrome signal with sync information. This information, along with mono audio, is available through the ribbon cable. The hdmyboy converts the digital video and the analog audio and sends it through the HDMI cable to the TV. The hdmyboy only supports mono audio because only a mono audio signal is necessary for the single speaker connected to the LCD PCB.
Unfortunately the Kickstarter campaign was not successful. However, the hdmyboy team still has some prototypes left here : http://www.hdmyboy.com/play/. They are very expensive however, (a bit too expensive for what it does) but should represent the best solution to obtain true Game Boy output without using an emulator. If they try another Kickstarter campaign again, then hopefully more people would be willing to contribute and get the price of this fine idea down.
Given a 1080p display, the hdmyboy can by default do 7x nearest neighbor scaling to give razor sharp graphics at the Game Boy's original aspect ratio. It can also do 12:7 scaling to give razor sharp widescreen graphics and occupy almost the whole screen if you prefer. Like the Super Game Boy it has 32 color palettes available to colorize the graphics. While the Game Boy's sprite and background tiles have 10 valid palette selections to choose from, the Super Game Boy (unless the game is enhanced) and hdmyboy only apply colors based on the actual color value of the outputted pixel.