Sync / csync
Sync / csync Considerations
Every video signal needs a sync reference so the display knows where each line and frame begins. With composite and S-Video this is bundled invisibly into the signal, but with RGB you must supply sync separately — and how you do it decides whether your picture is rock-solid or a wobbling mess.
The common sync options
- Composite video as sync: many cheap RGB SCART cables tap the composite output and use it for timing. It often works, but the leftover luma can cause faint vertical bars or instability on picky displays.
- Composite sync (csync): a dedicated sync signal with no picture data riding along. This is the cleanest, most reliable option and what most upscalers and RGB monitors prefer.
Some later console revisions output a sync signal that is weaker or differently shaped than early boards expect. On these, a basic cable may give an unstable image until a clean csync source is used.
Getting clean csync
A clean csync is usually achieved with a small circuit — often a sync stripper built around a dedicated sync IC — that extracts pure horizontal and vertical timing and removes the video content. Many quality aftermarket cables include this circuit inline, so you do not have to modify the console.
If RGB looks correct in color but rolls, tears, or shows interference bars, sync is almost always the culprit. Before rewiring anything, try a cable with proper csync — it resolves the majority of these complaints.