Document ID: TOS-WIKI-REF-009 Revision: 1.0 Author: ThisOldScot
Section_1: Overview#
In the Borders Workshop, we define “Sync” as the metronome of the video signal. It tells the display exactly when to begin drawing a new horizontal line and a new vertical frame. While standard RGB signals (Red, Green, Blue) carry colour data, they require a fourth signal to stay stable.
Modern scalers (OSSC, Retrotink 5X/4K) and professional monitors (BVM/PVM) are highly sensitive to “Sync Jitter.” This guide outlines the different methods of carrying sync and the logic behind selecting CSYNC for the ultimate “Borders Standard” visual output.
Section_2: Sync Modalities#
| Sync Type | Carrier Signal | Pros/Cons |
|---|---|---|
| Sync on Composite | Full Video Signal (CVBS) | Pro: Standard on all cables. Con: Heavy “checkerboard” interference. |
| Sync on Luma | S-Video Luminance (Y) | Pro: Cleaner than CVBS. Con: Not available on all console multi-outs. |
| CSYNC (Clean Sync) | Pure Timing Only | Pro: Perfect signal-to-noise ratio. Con: Requires specific logic or stripping. |
| RGSB (Sync on Green) | Green Channel (G) | Pro: Minimises wire count. Con: Rare outside of Sony/Arcade hardware. |
Section_3: The Restoration Protocol: Identifying the Pulse#
STAGE_3: 01 // The Signal-to-Noise Problem#
When using Sync on Composite, the sync pulses are buried inside the same wire as the colour information. Modern scalers often “struggle” to extract the timing pulse from the video noise, resulting in a shaky image or frequent sync-drops during bright flashes.
STAGE_3: 02 // The CSYNC Migration#
For consoles like the SNES or Mega Drive, we prioritise a dedicated CSYNC line.
- Protocol: Identify if the console outputs native CSYNC at the multi-out.
- NTSC SNES: Pin 3 is CSYNC (Ready).
- PAL SNES: Pin 3 is +12V (Hazard). Never use an NTSC CSYNC cable on a PAL console.
- Action: If CSYNC is missing, it must be generated via a Sync Stripper.
STAGE_3: 03 // The LM1881 Handshake (Sync Stripping)#
If a console (like the PS1 or N64) does not output clean sync, we integrate an LM1881 Macro-circuit.
- Logic: The LM1881 “listens” to the Composite Video line and extracts only the vertical and horizontal pulses, outputting a pure CMOS-level sync signal.
- Surgical Step: Mount the LM1881 inside the SCART head or a custom console-internal interposer.
STAGE_3: 04 // Impedance Matching (75-ohm vs TTL)#
- TTL Sync: ~5V Peak-to-Peak. High voltage used in arcade monitors.
- 75-ohm Sync: ~0.3V Peak-to-Peak. The standard for consumer TVs and scalers.
- The Fix: To convert TTL to 75-ohm, you must install a 470-ohm series resistor and a 10uF – 220uF capacitor on the sync line to prevent “Sync Over-driving” which can damage modern equipment.
Section_4: Technical Warning#
Safety_Warning
VOLTAGE HAZARD: Some PAL consoles (specifically the PAL Gamecube and SNES) output DC voltage on the pins where NTSC consoles output sync. Connecting a standard NTSC “CSYNC” cable to these consoles can send 12V directly into the sync-input of a £700 scaler, resulting in permanent I/O port failure. Always verify the System-Specific Pinout (TOS-BIBLE-APPX-01) before connecting new cables.
Section_5: Practical Application: Stabilising the “Jiggly” N64#
A Nintendo 64 was processed that exhibited “Sync Wobble” on an OSSC. Forensic analysis showed the use of a cheap “Sync on Composite” cable. By performing an internal RGB Mod with an integrated sync stripper and utilising a 75-ohm attenuated CSYNC cable, the image was stabilised to 100% rock-solid clarity.
Section_6: Heritage Logic Note#
While “Sync Stripping” adds complexity, the Borders Workshop authorises this as a Visual Preservation Requirement. High-fidelity signals allow for better digitisation and documentation of game art. We only use high-bandwidth shielded cabling (e.g., Coax-style) to ensure the newly cleaned sync signal does not suffer from external RF interference.
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