Hooking a Sega Outrun arcade PCB up to an AT(X) power supply and SCART TV
As it's slightly inconvenient to work on your Outrun PCBs while they're in your immovable deluxe sitdown cabinet, here's a simple and cheap way to hook them up to a regular (European) TV.
Disclaimer: Although mine seems to work, please build/use this at your own risk. And please verify and measure things before powering up, and preferably try first on some old 14" CRT rather than your brand new 60" UHD TV.
Parts
- Male 21-pin SCART (Euro-AV) connector
- 2x 2x5 IDC female connectors
- 10-wire ribbon cable
- AT(X) power supply. And one 4 pin male AMP MATE-N-LOK/Molex 8981 header with wires (salvage from old splitter cable).
- 8-wire shielded data cable, or if you can find it, cable with internal separate shielding for video and audio signals.
- 3x 390Ω resistors (¼W)
- 1x 300Ω resistor (¼W)
- 1x 470Ω resistor (¼W)
- 2x 6-pin female Molex KK 396 connectors, or salvaged AT mainboard power connector cables.
- Heat shrink tubing
Power
The standard sitdown powers both CPU and video boards with a single regulated 5V/10A supply. I'm using a AT(X) power supply as found in most junk PCs, as they're extremely available and can deliver plenty of current at a stable 5V. The AT variants power on with an external AC switch, the ATX versions need pin 16 on the motherboard power connector (green wire) to be shorted to ground (any black wire) in order to turn on.
A nice bonus of using an AT(X) PSU is that these also have +12V available, which can be used to switch the TV to 4:3 mode. Alternatively, one could use a voltage doubler circuit for this, if only +5V were available.
You can scavenge a male 4P AMP/Molex header (with wires) from an old CPU or chassis fan, or one of those splitter cables that you'll never use again anyway.On the PCB side, there are two identical 2x5 pin connectors, designated J on the CPU (top) board, and K on the video (bottom) board. I've used commonly available IDC connectors with ribbon cable for these. You may find that some of the notches need filing down in order to fit into the connector. Just make sure you label the top to avoid any confusion (and smoke and/or fire*) later on.
*) It may actually be a good idea to add a 10A fuse somewhere, since these PSUs can deliver a lot of current on the 5V output.
This is the pinout for connectors J and K:
| Pin | Pin | Description | To PSU AMP/Molex header |
| A1 | B1 | +5V | Pin 4 (red wire) |
| A2 | B2 | +5V | Pin 4 (red wire) |
| A3 | B3 | Not connected | - |
| A4 | B4 | Ground | Pin 2/3 (black wire) |
| A5 | B5 | Ground | Pin 2/3 (black wire) |
Video
The video output on connector H has higher ("arcade monitor") output levels than SCART needs, so we should bring them down using resistors. The R/G/B lines already have some output resistance, connected to the outputs of two 74HC273s (used as DAC) and the 3-state outputs of a 74LS125 (for shadows/highlights). Assuming ideal components (with VOH = 5V), we should put a resistor of no less than 345Ω in series.
CH1: Sync; CH2: Green (cable connected).Video connector H, video (bottom) board:
| Pin | Description | Output level | To SCART pin | SCART level | Series resistor |
| 1 | Red | 5V* | 15 | 0.7V | 390Ω |
| 2 | Green | 5V* | 11 | 0.7V | 390Ω |
| 3 | Blue | 5V* | 7 | 0.7V | 390Ω |
| 4 | Composite Sync | 5V** | 20 | 1V | 300Ω |
| 5 | Ground | - | 4, 5, 9, 13, 14, 17, 18, 21 (chassis) | - | |
| 6 | Ground | - | 4, 5, 9, 13, 14, 17, 18, 21 (chassis) | - |
*) Depending on load, and actual output voltage VOH of the ICs used.
**) Measuring (see scope image above) puts the actual maximum output voltage of the tested board at about 3.3V.
Audio
The stereo signal on N already is in reasonable range, and also already has a 4.7kΩ resistor and 1µF capacitor per channel, so we can connect these directly.
CH2: Left channel playing 'passing breeze'.Audio connector N, CPU (top) board:
| Pin | Description | Signal | To SCART pin |
| 1 | Left | ±0.7VPP | 6 |
| 2 | Ground | - | 4 |
| 3 | Ground | - | 4 |
| 4 | Right | ±0.7VPP | 2 |
| 5 | Mix | (not measured) | - |
| 6 | Ground | - | 4 |
SCART
Since we have +12V available on the PSU as well, we can set up the proper voltages on SCART pin 8 (+12V to select 4:3 mode) and pin 16 (+1..3V to switch to RGB input). This will usually automatically switch your TV to the right input channel when powering on the board.
| Pin | Description | Level | Impedance | Connect to (through resistor) |
| 2 | Audio In (Right) | 0.5V RMS | >10kΩ | Connector N, pin 4 |
| 6 | Audio In (Left) | 0.5V RMS | >10kΩ | Connector N, pin 1 |
| 7 | Blue | 0.7V | 75Ω | Connector H, pin 3 (390Ω) |
| 11 | Green | 0.7V | 75Ω | Connector H, pin 2 (390Ω) |
| 15 | Red | 0.7V | 75Ω | Connector H, pin 1 (390Ω) |
| 20 | Composite / Sync | 1V | 75Ω | Connector H, pin 4 (300Ω) |
| 8 | Status & Aspect Ratio | 9.5..12V: 4:3 | 75Ω | AMP/Molex +12V pin 4 (yellow wire) |
| 16 | Blanking / RGB | 1..3V: RGB | >10kΩ | SCART pin 8 (+12V) (470Ω) |
| 4, 5, 9, 13, 14, 17, 18, 21 | Ground | - | - |
AMP/Molex: pin 2, 3 (black wire) Connectors J, K: A4, A5, B4, B5 Connector H: 5, 6 Connector N: 2, 3, 6 |
Wiring diagram
When all put together, it should resemble something like this:
References
- SCART on Wikipedia
- SCART Pins and Voltage specs
- Molex KK® 396 Connector System
- SN74LS125A - Quadruple bus buffers with 3-state outputs
- 74HC273 - Octal D-type flip-flop with reset
