Here is the link to Jakks TV Games, where you can see their recreated Activision, Atari, and Namco games. (The latter includes PacMan!) My family had the original Atari 2600 home video game in the 1970s; I bought the Jakks Atari game for $32 at Urban Outfitters.

Like the other two games, the Atari game fits into a device that nearly duplicates the handheld controller for the original game. The Atari is just a joystick with one "fire" button. It would be the exact same size as the original joystick but for the extra space on the bottom needed for four AA batteries. Out of the back comes a cable with video and audio outputs. The look and feel of the joystick replicates the original exactly, down to the colors and textures of the rubber and plastic and the wobble of the fire button. Same for the play of...some of the games themselves; they seem to be based on original ROMs. However, there are differences. Here's an unhappy review.

So, this thing emulates the original game box (10" x 8" x 2.5"?), one joystick (no second player), and ten of the original game cartridges, including my favorite, Adventure, by Warren Robinett. I wonder how they do it. So does my screwdriver.

Here is the first stage of disassembly, with the top of the box, joystick paddle and fire buttons themselves removed:

The yellow disks are rubbery switches for joystick left, right, up and down, and fire. Next to the right switch is an adjustment potentiometer, hmm. On the front of the box are the controls that were on the original separate game box: power switch, reset, select (to choose game modes) and start. Above the power switch is a red power LED (there to remind you that the thing is battery powered).

Here is a top view with a little more of the circuit board exposed:

The "up" button has been peeled away from the circuit board (it's held in by two rubbery pegs or fingers), revealing the spiral switch contacts underneath. The yellow hats contain little carbon tablets that make the contact. On the left, the video output wires and RF choke (seen in the next picture) are wrapped in paper-backed foil RF shielding.

Here is the underside of the board, flipped left to right from the previous picture:

You can see the eight wires that connect to the board. On the left, top to bottom: power, reset, select, start, and ground. On the right, there are four pads labeled (top to bottom) Video, VGround, AGround and Audio. Only the audio ground is used. The output wires are wrapped around an RF choke and then get their own foil wrapper. You can see the yellow fingers sticking through from the other side.

The two fingerprint-sized black lumps on the upper part of the board cover two IC chips. These correspond to the areas just under, and just to the right of, the exposed "up" switch pad in the previous picture. I didn't try to scrape off the black epoxy to see the chips' innards. According to a friend who took his further apart, they are the video chip, and all the rest (processor, memory, I/O and ROM). Between the two chips you can see the clock crystal. It's labeled "27.000", which is almost 7.5 times the NTSC color carrier frequency. Eric Smith explains that 27 MHz is exactly twice a standard sample rate for digital video, so that many video chips use this frequency. Somewhere in the video chip, the 27 MHz is multiplied by the fraction 35 / 264 and put through a phase-locked loop to produce 3.579545 MHz.

The original game contained a 6502 processor chip, a chip with some I/O, RAM and timers, the video chip, and some glue circuitry. The earliest games were 2K, and later games (like Adventure) were 4K. Cartridges containing 8k had to be bank-switched, meaning that the cartridge only had twelve address wires, enough for 4096 locations, so one or two special locations switched between banks of 4096 bytes.

Probably there is between 32 and 64 K of ROM in the Jakks game-- small enough to still fit within the 6502's address space.

One mystery about the game is that the opening screen, before you select which of the ten games to play, contains lots of text and a couple multiple-color bitmaps, visuals that the original 2600 video chip couldn't produce. Were the games reprogrammed for a different video chip? That would be strange because CMOS versions of the 2600's video chip already exist, and software work costs money. Another possibility is that the original video chip is emulated with a bitmapped display and software. There are software 2600 simulators for the PC and other computers. And the WDC W65C02S processor, for instance, which is available as a component inside custom chips, runs at 14Mhz, ten times faster than the original game's 6502. (Not to mention the Open-source VHDL 6502 design for FPGA chips that might run as fast as 166 MHz.) Another possibility I like is that the video chip actually contains two different video circuits, one a clone of the 2600's, and the other some standard bitmap display, and a switch! It sounds strange but it might be cheaper than paying programmers.

The same informant who dissected his Jakks Atari game took apart one of the Intellivision 25-in-1 games. That game has different chip inside, to wit, the Nintendo (NES) on a chip, which implies a definite rewrite of the Intellivision games. Someone passed on a rumor that the Jakks Atari used the NES chip, but the NES isn't capable of the Atari sounds (nor the proper Intellivision sounds for that matter), and besides, the chip just looks different.

Oh, forgot to finish the story of the adjustment pot. Turn it too low and the image gradually fills with one kind of digital snow. The other way and another kind of distortion. If you have one of these games and you see a little vertical line to the right of the ball or player (mentioned in the review linked above), this adjustment will get rid of it.

Anyway, when the game is plugged into my deluxe modern TV at home, I don't get color at first. (I have seen other complaints to the same effect on video game related newsgroups.) I had hoped this adjustment would help. It doesn't in the obvious way--there is no point in the range where color appears. But while I was fiddling with it angrily, color suddenly appeared. It seems to be an effect of quickly twitching between snow and good signal. Something in the snow convinces the TV that the picture is color, and then the regular signal is good enough to keep the color locked in. This is bad because those adjustment pots aren't designed for constant use. But it's good because some of the games really need color to be playable.

So, just above the pot, in the outer case, I drilled a hole. Isn't it good, Norwegian wood.