If you want to connect your Atari 2600 or 7200 to a modern device you will need to make a small modification to the console to be able to use the composite signal instead of the native RF signal of these models.
What do you need?
The pinout in this figure is the RF modulator connector on the 2600 version.
GND is on pin 1, 5V is on pin 3 and the video signal is on pin 4.
In the diagram, the Vcc and GND signals represent only the levels that we have on the pin.
The resistor R3 is optional, if you see that you have the video signal too high then insert it to attenuate the level.
The diagram is the same but the pinout of the connector is different, on this version we have the GND on pin 1, the 5V on pin 2 and the video on pin 3.
PS. The audio part is not in the circuit, you just need to take the signal with a wire and bring it to its connector, you will see later how.
The Junior version is totally different, I left the connector on the schematic to facilitate pin mapping but in reality on this model we do not have the removable modulator block and therefore no connector to use.
Open your console by removing the screws on the bottom, if you have the 2600jr model be careful because it has plastic clips in the thinnest part that must be widened (trying not to break them) from the ventilation grille and has a flat cable for the buttons.
For the 2600 and 7800 versions, the modulator must be removed, for all versions, if you want a cleaner signal, some components must be removed.
Remove the following components:
Q201 (o Q202), L201, R222, R209 (o C209)
* if you want to put everything back as it was one day, I advise you not to remove them completely but to raise one lead of the resistors and capacitors. For the transistor, if you do not want to remove it completely, just raise its collector, while for the inductance which, being rigid, must still be removed but it can be attached to the pcb or the case with insulating tape so as not to lose it.
On some boards, the components may be slightly different.
Removed the components you can take the audio signal on the 1k resistor near the capacitor (yellow circle) and take it directly to the RCA connector. For convenience of connections, two RCA audio connectors (right and left) should be used connected to the same signal, so by connecting the cable to the TV we will have a mono signal, but we will hear it on all speakers instead of only on one side.
From the modulator connector, pins 1 (GND), 3 (+ 5V), 4 (Video) must be taken and connected to the amplifier board and from there the video signal will be taken to the RCA connector.
I used a board already prepared for the Atari 2600 pinout so that it could be soldered directly in place of the modulator avoiding other wires.
In this version the following components must be removed:
R209, Q202, L201, R216
The audio signal must be taken on the R209 resistor (sign highlighted in yellow), while the video and power signals must be taken from the pcb where the modulator has been removed (same pinout as the 4 switch version).
On this model it is probably not possible to directly solder the board to the pcb due to the metal shield very close, in case it is advisable to use wires to connect the board.
The rest is as for the previous version, bring the audio and video signals to the connectors and close everything!.
* Always be careful to pass the audio cable without squeezing it too much under the metal shield.
For both versions the following signals are then taken and brought to the board to mix the signal.
For convenience i will re-publish the schema and there i map the pins.
Pin1 of the board goes to GND (photo Atari)
2 goes to the resistance labeled N.2
the 3 goes on the pin labeled 15
the 4 on the number 12
5 on number 10
the color signal goes to the resistance labeled color
the audio signal (purple circle) can be brought to the RCA connectors
The rest is always the same as the previous versions, the video signal will come out from the card and it will be brought with wires to the RCA connector.
On this version the following components must be removed:
L6, R32, R33, R62, Q8
the audio signal can be taken from the right pins of the R33 and R32 resistors, join them and take them to the RCA connector (see photo below).
The pinout of the modulator we removed is not the same as the Atari 2600 version but is the following:
3: Composite video
If you are using the board seen previously, just shift the pins by one position, then use a 3-pin header starting from pin #2 of the board (so on the board we will have soldered pads 2,3,4 starting from the left). We make a bridge with the tin between pin1 and 2 of the board (so the GND of the board will be present at pin 2 which however is not used on the mod for the 2600 version)
So now we can solder the board directly to the Atari pcb using pins 1,2,3 of the old modulator.
If you do not use this board, just bring the relative signals of the pcb to the circuit you have built or bought, in the diagram in the figure for example: pin 1 is the GND (goes to pin 1 Atari), 3 is + 5V (goes to pin 2 Atari), 4 is video (goes to pin 3 Atari).
Once again as mentioned above, we bring the audio and video signals on the RCA connectors to finish the modification.