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4.13
5200 CROMA/LUMA (COMPOSITE VIDEO) AND AUDIO OUTPUT MODIFICATION


Differences between 2-port and 4-port consoles:

Not surprisingly, there are very few appreciable differences between the 2-port and 4-port variations of the 5200. For the purposes of this article, they are considered to be identical.

Where to get signals:

Most of the components do not have visible labels on the board's silkscreen, so giving component numbers is not useful. In the upper right corner of the area of the board that's covered by the shielding, there is a horizontal row of components.


               o  o  o  o  o  o  o  o  o  o  o  o
               |  |  |  |  |  |  |  |  |  |  |  |
               C  R3 R2 R1 D  R  R  R  R  R  R  R
               |  |  |  |  |  |  |  |  |  |  |  |
               o  o  o  o  o  o  o  o  o  o  o  o
                              ^  ^  ^  ^  ^  ^
                              |  |  |  |  |  `-Chroma
                              |  |  |  |  `----Luma 1
                              |  |  |  `-------Sync
                              |  |  `----------Luma 0
                              |  `-------------Luma 2
                              `----------------Luma 3
There is a row of components to the right of the GTIA (C014805) and below a cluster of inductors and transistors.


                o  o o o o o o o o o o
                |  | | | | | | | | | |
               R40 R R R R R C R R C C
                |  | | | | | | | | | |
                o  o o o o o o o o o o
                               ^
                               `--Audio
Luma output:

The Luma signal needs amplification to be useful. After probing around on an Atari 800 (a close relative to the 5200 that conveniently has Croma/Luma outputs built-in), I realized the amplifier circuit they used is remarkably similar to the one attributed to Thomas Clancy in the Classic Atari Game Systems FAQ. Rather than try to copy the circuit on the Atari 800 or design one from scratch, I decided to use the one given there. The only significant difference is the addition of another level of luminance.

Materials Needed: 


   100uF capacitor
   10uF capacitor
   10 ohm
   (2) 75ohm - an 82 ohm works well (RS 271-1107)
   750 ohm
   1.6 kohm
   2   kohm
   4.7 kohm
   9.1 kohm
   18  kohm
   36  kohm
   CR - low power silicon diode (RS 276-1122)
   Q - 3904 or equivalent (RS 276-2016)
   RCA jack

                                 o+5V
                                 |
                                 |  +
                                 |---|(----,
                                 |  100uF  |
                                 |         \/ GND
                                 |
                                 |             10uf
                                 |---/\/\/---,--|(--,
            CR1  750       1.6K  |    10     | +    |
    Sync --|<]--/\/\/-,  ,-/\/\/-`           |      \/ GND
            4.7K      |  |        ___/-------`
  Luma 3 ---/\/\/-----|  |     Q /|/c\
            9.1K      |--|------(b|   )                   RCA jack
  Luma 2 ---/\/\/-----|  |       \|\e/          75        __
            18K       |  |           \-----,---/\/\/-----O__ LUMA
  Luma 1 ---/\/\/-----|  |  2K             |             |   OUTPUT
            36K       |  `-/\/\/----/\/\/--`         GND \/
  Luma 0 ---/\/\/-----`          |    75
                             GND \/
Chroma output:

In my experience, the 5200's chroma signal is sufficiently strong that it can be used without amplification. On my own 5200, I ran the chroma through a 2kohm resistor to "take the edge off," then a 1uF capacitor to filter the DC voltage off. Play around with the resistance there to find what suits you.


                                                          RCA jack
             2k     1uF                                   __
  Chroma ---/\/\/---|(-----------------------------------O__ CHROMA
                                                         |   OUTPUT
                                                     GND \/

Audio output:
   This is just a capacitor to filter out the DC voltage.

                                                          RCA jack
               1uF                                        __
  Audio ------|(-----------------------------------------O__ AUDIO
                                                         |   OUTPUT
                                                     GND \/
Composite video output:

To gain composite output, just tie the Luma and Chroma outputs together into a single output.

Where to put it:

I mounted the circuits on a small project board from Radio Shack, tapping into the appropriate points on the 5200 board with a length of ribbon cable. I then tucked the board into the controller storage space at the back of the console and ran the output signals to three RCA jacks I had mounted in the removable expansion interface cover. That way the only permanently modified/damaged piece (the cover) is also one that is easily replaced.

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