RGB SCART vs RGB‐Modded CRTs — How Blanking & Sync Work - ZFEbHVUE/Batocera-CRT-Script GitHub Wiki
📺 RGB SCART vs RGB-Modded CRTs — Understanding Sync & Blanking
Many retro gamers today are RGB-modding composite-only CRTs because North America never had SCART TVs.
This guide explains the key difference between factory SCART TVs and RGB-modded CRTs — so you can pick the right VGA to SCART adapter and avoid a blank or composite-only picture!
✅ 1️⃣ Factory SCART TVs
- SCART pin 20: Carries CSYNC (composite sync).
- SCART pin 16: Carries blanking voltage (~1–3 V) that tells the TV to switch from composite to RGB mode.
- SCART pin 8: Optional — ~12 V to signal 4:3 or 16:9 aspect ratio.
📌 If you don’t supply blanking voltage, the TV defaults to composite input — your RGB signal is ignored!
✅ 2️⃣ RGB-Modded Composite-Only CRTs (US)
- RGB mods inject R, G, B and sync directly into the jungle IC.
- A blanking signal (often called YS or BLANK) tells the jungle IC to switch from internal composite to external RGB input.
- Many MUX boards force blanking always on by wiring it to +5 V internally.
- Others connect the blanking line to SCART pin 16, expecting the SCART cable to supply the voltage — exactly like a factory SCART TV.
📌 If your mod relies on SCART pin 16 but your adapter doesn’t supply blanking — you’ll just get composite.
🔌 How It Looks — Simple Diagrams
✅ Factory SCART TV (Europe)
[ PC / GPU RGBHV ]
|
[ Sync Combiner ]
|
[ SCART Cable ]
|
--------------------------
| SCART pin 20 → CSYNC
| SCART pin 16 → 1–3 V blanking → Jungle IC RGB mode
| SCART pin 8 → 12 V aspect (optional)
| SCART pins 15/11/7 → RGB lines
➡️ Needs: Sync combiner and blanking voltage on pin 16.
✅ RGB-Modded CRT (RGB MUX)
[ PC / GPU RGBHV ]
|
[ Sync Combiner ]
|
[ SCART Cable ]
|
--------------------------
| SCART pin 20 → CSYNC
| SCART pin 16 → used if mod expects it
| SCART pins 15/11/7 → RGB lines
|
+--> [MUX board]
|--> Jungle IC RGB pins
|--> Jungle IC blanking pin:
forced +5 V internally OR uses SCART pin 16
➡️ Needs:
- If blanking is hard-wired → only sync combiner needed.
- If blanking relies on pin 16 → must use adapter that outputs 1–3 V on pin 16.
RGB MUX Chart
🗂️ Diagram: Left = Factory SCART TV • Right = RGB-MUX modded CRT
🛠️ How to Check Your Mod
✅ Does your RGB mod diagram:
- Show SCART pin 16 connected to the jungle blanking pin?
- Or is blanking forced high inside with a resistor or switch?
✅ Which Adapter Do I Need?
| Scenario | Recommended Adapter | Combines Sync | Provides Blanking |
|---|---|---|---|
| Factory SCART TV | VideoAMP, ArcadeForges - UMSA, or Retro Upgrades - VGA2SCART | ✅ | ✅ |
| RGB-Modded CRT with forced blanking | HD15-2-SCART | ✅ | ❌ |
| RGB-Modded CRT relying on pin 16 | ArcadeForges - UMSA, or Retro Upgrades - VGA2SCART | ✅ | ✅ |
ℹ️ For factory SCART TVs, recommended options are listed in order:
1️⃣ VideoAMP — ideal first choice
2️⃣ UMSA (Ultimate SCART Adapter) from Arcade Forge
3️⃣ VGA2SCART Sync Converter from Retro Upgrades
🧪 Real-World Testing: Does Your VGA Output Blanking Voltage?
Some VGA to SCART adapters rely on pin 9 of the VGA connector to provide the 1–3 V blanking signal to SCART pin 16. But not all GPUs or adapters output voltage on pin 9. Here's what testing revealed:
✅ DVI-I to VGA (Native Radeon Output)
Using a DVI-I to VGA adapter on a Radeon R7 250, pin 9 successfully outputs 4.93 V — suitable for blanking:
- ✅ Confirmed working: Good choice if you're using an adapter that routes pin 9 to SCART pin 16 (e.g. Mike Chi's VGA2SCART or Retro Upgrades model)
❌ HDMI to VGA DAC — No Voltage on Pin 9
Two separate HDMI DACs tested showed 0.00 V on pin 9:
- ⚠️ Blanking will not work unless you inject voltage manually or use an adapter like UMSA or VideoAMP that handles it externally.
- 💡 If you're using a DAC, consider a SCART Sense Injector from ZedLabz or equivalent.
📦 Adapter Wiring: Mike Chi VGA2SCART vs HD15-2-SCART
🟢 Mike Chi’s VGA2SCART v2.0
- ✅ Passive sync combiner
- ✅ Connects VGA pin 9 to SCART pin 16
- ✅ Good for SCART TVs or mods that rely on pin 16 for blanking
🔴 HD15-2-SCART
- ❌ Does not connect VGA pin 9 to SCART pin 16
- ✅ Combines sync, but no blanking voltage
- ⚠️ Works well only with mods that force RGB mode internally
“HD15-2-Scart doesn’t provide blanking but if the source does on pin 9 and the user has a fully wired VGA cable then they might be ok... but apparently it does NOT connect VGA 9 to SCART 16” — MarcoRetro
🧵 Reddit Confirmation
“I just opened mine up and can see that USB and VGA pin 9 are routed to a jumper to blanking... HD15-2-SCART on the other hand doesn’t route anything to SCART pin 16. No blanking for that one.” — r/crtgaming user
🧠 Summary: Adapter vs Blanking Behavior
| Adapter | Blanking (Pin 9 → Pin 16) | Sync Combiner | Notes |
|---|---|---|---|
| VGA2SCART (Mike Chi) | ✅ Yes | ✅ Passive | Works with SCART TVs and some RGB mods |
| HD15-2-SCART | ❌ No | ✅ Passive | Fine for mods that force blanking |
| HDMI DACs | ❌ No output on pin 9 | Varies | Needs UMSA, VideoAMP, or sense injector |
📌 This section validates why certain adapters only work under specific conditions and offers measurable evidence using a multimeter. Real-world testing shows that not all "VGA" outputs are equal — and DACs often drop pin 9 voltage entirely.
📚 Proven Sources
This guide is based on practical modding references:
- 🔗 CRTDatabase: RGB MUX Modding
- 🔗 Sector Guide: RGB MUX Boards & Theory
- 🔗 Recommended Adapters, Sync Solutions & Transcoders
🧩 Key Takeaways
✅ For factory SCART TVs — always supply sync + blanking.
✅ For RGB-modded CRTs — if blanking is forced internally, a simple sync combiner is fine.
✅ If your mod uses SCART pin 16 for blanking — your adapter must output 1–3 V on pin 16!
❓ FAQ
Why does my modded CRT still show composite instead of RGB?
Check if your MUX board relies on SCART pin 16 for blanking. If your adapter doesn’t supply 1–3 V on pin 16, your TV may stay in composite mode.
Do I always need a sync combiner?
Yes — VGA output is RGBHV (separate H+V sync), but SCART RGB expects CSYNC. A combiner merges H+V into CSYNC.
Can I add blanking voltage myself?
Yes — you can run a small 1–3 V source (e.g. USB 5 V with a resistor) to SCART pin 16, or force blanking internally in your mod.
What if my mod always forces RGB mode?
Perfect — then you don’t need the adapter to supply blanking at all. A simple sync combiner like the HD15-2-SCART works great.