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Universal Sync Box — RED DSMC2 Dip Switch Settings and Faulty 3BNC Cables

CONFIRMED BOTH SYNC BOX

Summary

The Universal Sync Kit label says "RED DSMC2" but does not distinguish between different RED expander types. The correct dip switch setting depends on the I/O module attached to the RED brain, not just the camera generation. Additionally, 3BNC breakout cables go intermittent before failing completely — a faulty cable can cause sync to appear non-functional when the box and camera are fine.

Symptoms

  • Sync will not connect on a RED DSMC2 camera despite correct dip switch position
  • Green sync LED on the sync box does not light, or lights only briefly when cable is wiggled
  • Sync works fine with other cameras (e.g., Komodo) on the same sync box
  • Intermittent sync — connection flickers or drops randomly

Systems Affected

BOTH
  • MRMC Universal Sync Kit (Universal Sync Box / Universal Sync Cable)
  • RED DSMC1 cameras
  • RED DSMC2 cameras — varies by I/O expander module
  • Also covers: ARRI, Phantom (for complete dip switch reference)

The Label Problem

The label printed on the Universal Sync Kit says "RED DSMC2" for one dip switch position. This is misleading — it does not account for the different I/O expander modules used with DSMC2 bodies. The correct setting depends on which expander is fitted, not which generation the body is.

"It's been brought to my attention that the label instruction for the dip switch position for RED refers to older models (DSMC1) but needs to change for newer models (DSMC2). We will get this updated for the next batch of cable kits." — Gordon (MRMC), 2023-06-06

Correct Dip Switch Settings

Camera / Expander Trig Sync
ARRI (all) 1 0
Phantom 1 1
RED DSMC1 (all body types) 0 1
RED DSMC2 — Base Expander 0 1
RED DSMC2 — V-Lock I/O Expander 1 1

DSMC2 Base Expander ≠ DSMC2 V-Lock Expander

The Base Expander and V-Lock I/O Expander look nearly identical on the back of a RED brain. The sync port functionality is completely different. Check which expander is actually fitted before setting the dip switches.

Why they differ

"The 'BASE EXPANDER' module requires a 3.3V signal from the Universal Sync Cable in order to trigger the camera. The dip switch position for this is 'Trig. 0 - Sync 1' just like DSMC1 camera bodies. The 'V-LOCK I/O EXPANDER' module uses a contact closure style circuit to trigger the camera. The dip switch position for this is 'Trig. 1 - Sync 1'." — jacob, 2023-06-08

If unsure which expander you have, look up the Communication Ports section of the RED DSMC2 user manual (approximately page 200) to identify which trigger circuit type the expander uses.

RED DSMC2 V-Lock Expander — Cable Connections

When using the V-Lock I/O Expander (Trig 1 / Sync 1), the cable connections are:

  • The yellow sync BNC on the trigger cable → CTRL port on the camera (sync out signal)
  • The white BNC → SYNC port on the camera (run/stop)

Inside RED camera menus: Settings → Setup → GPIO/Sync → set GPO Function to Sync Out.

"The breakout cable to have connected to the yellow sync BNC on the trigger cable will plug into the 'CTRL' port on the camera for sync out signal. The breakout connector you have connected to the white BNC will plug into the 'SYNC' port on the camera for run/stop. Inside the RED menus, navigate to Settings > Setup > GPIO/Sync and make sure the GPO Function is set to 'Sync Out'." — jacob, 2025-03-06

Faulty 3BNC Cables

If sync remains non-functional despite correct dip switches and connections, suspect the 3BNC breakout cable.

3BNC cables go intermittent before failing completely. Symptoms:

  • Sync LED lights only when the BNC connector is physically pushed in or held at an angle
  • Sync connects briefly then drops
  • The sync box works fine with another camera (e.g., Komodo)

"I saw the green light on the sync box come to life for just a flash. I wiggled the connection around, pushing the connectors together just a bit and I could get the green light to stay on as long as they were pushed together a bit... Plugged in the other 3-BNC and couldn't get it to turn on no matter what I did. So I'm guessing I have two bad 3-BNC cables?" — sdelahoyde, 2025-03-07

"Ordered two new 3BNC cables, plugged the first one in and instant sync!" — sdelahoyde, 2025-03-10

Check all 3BNC cables individually. If one works and another does not, the cable is faulty — not the camera or sync box.

Diagnostic Quick Reference

  1. Confirm which RED expander is fitted (Base vs V-Lock I/O).
  2. Set dip switches per the table above.
  3. Check the green sync LED — it should flash at the camera's frame rate when connected.
  4. If LED does not light: wiggle the 3BNC connector at both ends. If the LED flickers when wiggled, the cable is faulty.
  5. Try a known-good 3BNC cable.
  6. If using ARRI for comparison — note that ARRI must be on 24V AC/DC power for sync to be detectable (see ARRI 24V PSU Required).

Source: talk.mrmoco.com — Universal Sync kit - RED camera models — Posts by Gordon (MRMC) and jacob, 2023-06-06 to 2023-06-08

Source: talk.mrmoco.com — Red Helium - Sync Won't Connect to Flair / Send Pulse — Posts by sdelahoyde, jacob, Gordon (MRMC), 2025-03-06 to 2025-03-10

Official Documentation

Camera Sync and Trigger V2 — Sync Box Setup and Camera Wiring

Camera Triggering and Synchronisation

Watch on YouTube · 08:01

Triggers Box and Bloop

Watch on YouTube · 05:22

Revision History

Date Change Editor
2026-05-29 Initial extraction from forum topics 1308 and 1770 Tom D / Claude Code