Atari 5200 AV Output Upgrade

A four-port 5200 board; the RF modulator and its cable are at the right

Every Atari 5200 leaves the factory with RF output only, through an RF modulator with a channel select switch. An AV output upgrade takes composite video, S-video and audio from inside the console instead. The community has used two approaches: tapping the console's own video and sound circuits, and fitting the Ultimate Atari Video (UAV) board. On four-port consoles a third modification, a separate power jack, is usually done at the same time so that the CX522 switchbox is no longer needed.

The procedures below are summaries of the cited community guides. Read the guide for your board before cutting or lifting anything.

How the 5200 makes its picture

Atari's schematic and service manual show the signal path:

• The GTIA (U5) produces three luminance lines and sync. They pass through the 4050 hex buffer at U1 (A1 on the later boards) and are summed through R23, R24 and R25 into the RF module. Pull-ups R18 to R20 sit on the GTIA side.
• The colour signal leaves GTIA pin 21 at about 4 V peak-to-peak, passes C11 and R28 and is amplified by Q3, whose output joins the luminance through C9 and R31 at RF module pin 4. R8 is the colour adjustment.
• The 4.5 MHz sound carrier comes from the oscillator around Q4 and L1, driven from POKEY (U7) pin 37.
• Sheet 2 of the schematic draws the modulator module (CA012174) with a "composite signal in" point; the console's composite video exists only as that input to the modulator.

Video lines at the 4050 (FD100127 p. 4-16)

Line	GTIA pin	4050 input	4050 output	Summing resistor
LUM0	31	3	2	R23
LUM1	22	7	6	R24
LUM2	23	11	12	R25

The 4050 also buffers sync, on its way from GTIA pin 25 to R22, and the CPU and ANTIC reset lines.

UAV board

The UAV was designed by Bryan Edewaard, who later sold the rights to the revision D board to The Brewing Academy (TBA), which now makes it for the Atari 8-bit computers and the 2600, 5200 and 7800. TBA describes it as having its own regulator, a three-channel video amplifier for 75 Ω loads, pixel re-clocking of the luminance lines and a chroma-shaping circuit, with a pot to set the chroma-to-luma phase and a jumper to invert the chroma. It plugs into the 4050 socket. The board has no audio circuit.

Board-specific notes

UAV fitting by board

Board	4050	Notes
CA021374 (two-port)	Can be removed and the UAV fitted in its place	TBA sells an "up" plug-in version with the terminal strip on top, for room beside POKEY in most two-port consoles
CA018087 and CA020108 (four-port)	Usually has to stay in circuit: piggy-back the UAV on it, or mount the 4050 on top of the UAV in the socket	ConsoleMods says very few four-port consoles work without the 4050 and that it cannot be predicted which; TBA's "down" plug-in version puts the terminal strip underneath to clear the four-port shield

Connections

The ConsoleMods guide, based on Ivory Tower Collections' instructions:

1. Set the UAV jumpers for the 5200.
2. Fit the UAV in the 4050 position by one of the methods above, with "The Brewing Academy" text to the right.
3. Take colour-in from the south leg of R17 to the UAV's "Co IN" terminal. TBA's manual gives GTIA pin 21 or the near end of the right-hand resistor in the row behind the GTIA.
4. Wire the chroma, luma and composite outputs to the jacks, with separate ground wires for the video and audio jacks.
5. For audio, wire a 10 µF capacitor in series with a 2 kΩ resistor from the north leg of R50 to both audio jacks. The 5200 has mono sound.

ConsoleMods suggests the unused expansion bay cover at the rear left of the case for the jacks, and notes that the RF shield must be bent, cut or have its expansion-bay piece removed to route the wires.

If the picture is wrong

• Black and white only, with every connection good: ConsoleMods reports taking colour from the south side of the top right-hand resistor on the board instead.
• Colour that cuts in and out: turn the blue pot on the UAV to adjust the chroma phase until it holds.
• TBA's manual mentions a program by Bryan for adjusting the colours on 5200 and 8-bit installs.

Removing the switchbox (four-port)

On most four-port consoles the RF cable also carries the DC supply, so the console only works with the CX522 switchbox. Some late four-port consoles, and every two-port, have their own power jack. ConsoleMods and Console5 describe the same bypass:

1. Remove L8, the inductor between the RF/power cable and the rest of the supply.
2. Fit a DC jack in the case, near the channel switch where the two-port has its jack.
3. Wire the jack centre through a 1N4001 diode (banded end towards the board) to the lower via of L8, and the jack sleeve to ground. Put a 0.1 µF capacitor across the jack.
4. Optionally replace C45 with the value for the board (47 µF or 4700 µF, 25 V).
5. Test with an ordinary switchbox or RF adaptor before reassembly. The RF cable can then be removed if the console will only be used through the AV outputs.

ConsoleMods says the original power pack, or any 9 to 11.5 V 2 A centre-positive DC supply with a 5.5 × 2.5 mm plug, will run the console. It warns against the 400 and 800 power supplies, which deliver AC. Atari's own Tech Tip 6 gives the same warning for the stock four-port.

Related pages

• Atari 5200
• Atari 5200 General Maintenance
• Atari 5200 Troubleshooting Guide
• Atari 5200 Capacitor Replacement Guide
• Atari 2600 Composite Video Mod
• Atari 7800 Composite Mod