RGB SCART Cables Explained: Sync Types, Shielding Quality, and Identifying Fake Cables

The most common mistake in a retro gaming setup is buying the wrong RGB SCART cable. A cable that carries the wrong sync type or lacks proper shielding will produce a picture with rolling, dropouts, or a 50Hz hum in the audio that no scaler can fix. The electrical standard is fixed, the IEC 60933-5 pinout from 1992, but the market sells cables that ignore it. Understanding RGB SCART cable sync types shielding and how to avoid fake cables is what separates a clean 240p image from a signal that damages equipment.

The 21-pin SCART interface is a durable specification. Pin 7 carries the widescreen switching voltage: 0-2 V for 4:3, 5-8 V for 16:9, and 9.5-12 V for the forced 16:9 mode on some European TVs. Pin 16 carries the blanking signal that tells the TV to switch from composite to RGB mode, 0-0.4 V for composite, 1-3 V for RGB. These voltages have not changed since 1992. A cable that does not deliver them correctly will either show a black screen or force the TV into the wrong input mode.

JP-21 vs RGB SCART: The Dangerous Mix-Up

JP-21 and RGB SCART use the same physical plug but different pinouts. Plugging a JP-21 cable into a European SCART input can route 12 V to a signal line designed for 0.7 Vp-p, damaging the machine's video encoder. The distinguishing feature is the pin assignment for sync and audio. A Japanese Super Famicom (NTSC-J) expects the JP-21 specification. An original European SNES expects the IEC SCART specification. Using the wrong cable is not a picture-quality issue, it is an electrical risk. Check the machine's region and motherboard revision before buying.

Three sync types exist on RGB SCART cables, and each behaves differently with a scaler like the RetroTINK 5X-Pro or the OSSC. The RetroRGB specification documents all three, and the choice affects sync stability, not image sharpness.

Csync (Clean Composite Sync)

Csync is a dedicated sync signal on a separate wire, isolated from the video signal. The SNES NTSC provides csync on pin 3 of the AV Multi Out. The Sega Saturn provides it on pin 1. The Sega Genesis Model 2 has a dedicated csync line on pin 5 of the AV port. A cable wired for csync gives the scaler the cleanest sync edge, which reduces the chance of sync dropout during a full-white flash. The SNES PAL outputs 12 V on pin 3 on some motherboard revisions, which requires attenuation, a resistor in the cable, before it reaches the 5 V-tolerant scaler input. Without it, the scaler's sync circuit can be damaged.

Sync-On-Luma

Sync-on-luma pulls the sync signal from the luminance channel of an S-Video signal. This is the method for machines that lack a dedicated csync line, such as the original PlayStation and PlayStation 2. The sync is embedded in the luma waveform, and most scalers can extract it. The trade-off is that luma sync can be noisier than csync, and some scaler firmware versions handle it less reliably. The RetroTINK 5X-Pro accepts it, but the OSSC may require a sync stripper like the LM1881 to clean the signal for certain machine revisions.

Sync-On-Composite

Sync-on-composite uses the composite video signal as the sync source. This is the most common wiring in cheap cables because it requires only one wire for both video and sync. The problem is that the composite video signal carries colour burst information that can interfere with the scaler's sync detection. The result is a stable picture on a CRT but sync drops on a digital scaler, especially during scenes with high luminance changes. The Sega Genesis Model 1 has no dedicated csync line on its AV port, so many cables fall back to composite video sync. A proper cable for the Model 1 should include an LM1881 sync stripper inside the SCART head to output csync.

Csync is the preferred sync type for any machine that provides it. The sync edge is cleaner, the scaler locks faster, and the failure mode, sync dropout on white flashes, is less common. The SNES csync dropout issue is well documented: a cable that uses composite video sync will lose sync during the flash transition in Super Metroid or the white screen between levels in Super Mario World. A csync cable, properly attenuated, eliminates that.

Sync-on-luma is the fallback for machines that do not output csync. The PlayStation 1 and 2 require it unless you install an internal csync mod. The picture quality is identical to csync in normal use, but the sync is more sensitive to cable length and shielding quality. If you use a sync-on-luma cable longer than 1.5 metres, expect occasional sync drops on a scaler with tight tolerance like the OSSC. The fix is a shorter cable or an external LM1881 sync stripper inline.

Shielding quality determines whether you hear a 50Hz or 60Hz hum through the audio. The failure mode is ground loop hum: an audible buzz that changes pitch with the video signal. Community documentation from RetroRGB and the Shmups Forum attributes this to cables that use a single ground wire for both audio and video return paths. A properly shielded SCART cable uses coaxial shielding for each RGB channel and a separate twisted pair for the audio channels. The outer braid should connect to the shield pin on the SCART plug at both ends.

The Insurrection Industries cable specification is the reference point. Their cables use 75-ohm coaxial conductors for each RGB line, a ferrite bead on the sync line, and a full braided shield over the entire bundle. The HD Retrovision component cables use a different approach, they integrate a transcoder in the cable, but the shielding principle is the same: separate the audio return from the video ground to prevent hum injection. A cheap cable from a stall in Sham Shui Po's Golden Computer Centre will skip the coaxial shielding and use a single drain wire. That cable will produce a buzz at 50 Hz on any amplifier connected to the scaler.

A fake or incorrectly wired cable will damage equipment. The electrical risk is real: a cable that routes 12 V from pin 8 to a signal line rated for 0.7 Vp-p will destroy the machine's RGB encoder. The identification method is to check the wiring against the machine's pinout, not the SCART end. The SCART end follows the specification; the machine end varies.

Open the cable at the machine connector end. Look for a resistor on the sync line for machines that need attenuation, the SNES PAL and the Sega Genesis Model 1 require it. Look for a capacitor on the RGB lines for machines that output a DC offset. The RetroRGB cable specification lists each machine's requirements. A cable that does not match is a fake.

The physical signs: a fake cable often uses a moulded plug that cannot be opened, a thin wire gauge (28 AWG or smaller), and no ferrite bead near the SCART head. The SCART plug should have metal shielding over the entire shell, not plastic. A plastic-shell SCART cable that weighs less than 30 grams is almost certainly unshielded. Do not plug it into a scaler that costs more than the cable.

The JP-21 and RGB SCART pinouts differ on the sync and audio pins. In the European specification, pin 19 carries composite video out and pin 20 carries composite video in. In the JP-21 specification, pin 20 carries the composite sync signal and pin 19 is unused. Plugging a JP-21 cable into a European SCART input routes the sync signal to the audio return path on some equipment. The result is a loud hum and potential damage to the audio input circuit.

The physical plug is identical. There is no keying difference. The only way to tell them apart is the labelling on the cable or the device. A Super Famicom sold in Japan expects JP-21. A European SNES expects IEC SCART. If you buy a Super Famicom in Hong Kong from a second-hand shop that does not specify the cable type, assume it comes with a JP-21 cable. Replace it with a correctly wired cable before connecting it to a RetroTINK or OSSC. The scaler's SCART input is wired for the European specification, and it will accept JP-21 signals only if the pinout is corrected by an adapter that reroutes the sync line.

The LM1881 sync stripper is a small IC that extracts csync from a composite video or luma signal. You need it when your machine outputs composite video sync and your scaler requires csync. The OSSC accepts composite video sync, sync-on-luma, csync, and sync-on-green, but some machine revisions output a sync signal with a voltage level that falls outside the scaler's tolerance. The SNES NTSC 1CHIP revision is known for a sync voltage that drops during white frames, causing the OSSC to lose lock for 2-3 seconds. An LM1881 circuit in the cable or inline normalises the sync edge and prevents the dropout.

The Sega Genesis Model 1 requires an LM1881 if you want csync. The machine does not output a dedicated csync line, so the cable must strip it from the composite video. A properly wired SCART cable for the Model 1 includes the LM1881 inside the SCART head. Without it, the scaler receives composite video sync, which is less stable and more prone to noise. The RetroTINK 5X-Pro can handle composite video sync, but the OSSC is stricter. If you use an OSSC with a Genesis Model 1, buy a cable with an integrated LM1881 or expect sync drops.