The monitor's showing sparkles. Or black. Or some weird artifact that shouldn't be there.
Before you start swapping cables, let's figure out what's actually broken.
The Troubleshooting Mindset
Signal problems have three possible sources:
- The source (camera, playback device)
- The cable (and connectors)
- The destination (monitor, recorder, switcher)
Cables get blamed for everything, but they're only responsible for about a third of problems. Before you condemn a cable, rule out the other two.
Symptoms and What They Actually Mean
Complete Black/No Signal
Likely causes:
- Source isn't outputting (wrong output selected, not recording)
- Destination input not selected
- Format mismatch (12G output to 3G-only input)
- Cable open (broken conductor)
- Connector not fully seated
What to check first: Confirm the source is actually outputting signal. Then check that you're on the right input at the destination. THEN check the cable.
Intermittent Dropouts
Likely causes:
- Loose connector (not clicked in fully)
- Damaged connector (bent pin, worn BNC lock)
- Cable damage at flex point
- EMI interference
- Marginal cable length (at edge of spec)
What to check first: Wiggle the connectors. If dropouts happen when you touch them, that's your culprit.
Sparkles (Random Bright Pixels)
Likely causes:
- Signal degradation (cable too long, poor quality)
- EMI interference
- Impedance mismatch somewhere in the chain
- Damaged cable shielding
What to check first: Try a shorter cable. If sparkles go away, your run is too long or your cable quality is insufficient.
Color Problems (Fringing, Wrong Colors)
Likely causes:
- High-frequency signal loss (copper-clad steel cables)
- Severe impedance issues
- Monitor calibration (not the cable)
- Format/colorspace mismatch
What to check first: Same cable, different monitor. If colors are fine on monitor B, it's not the cable.
Image Tearing/Rolling
Likely causes:
- Sync issues (not usually cable-related)
- Format mismatch between source and destination
- Frame rate confusion
- Ground loop (rare with SDI, but possible)
What to check first: Verify source and destination are set to the same format and frame rate.
The Isolation Method
The fastest way to find the problem:
- Swap the cable with a known good one. Problem fixed? It was the cable.
- Swap the source. Different camera, same cable, same monitor. Problem moves with the camera? Not the cable.
- Swap the destination. Same source, same cable, different monitor. Problem goes away? Not the cable.
This takes maybe 5 minutes. It's faster than guessing.
Common Non-Cable Problems That Look Like Cable Problems
Format Mismatch
Camera outputting 4K60 12G-SDI to a monitor that only accepts 3G-SDI. Monitor shows black or garbage. Not a cable problem.
Fix: Check specs on both devices. Match formats.
Wrong Output Selected
Camera has multiple SDI outputs. You're plugged into SDI 2 but only SDI 1 is active. Black screen. Not a cable problem.
Fix: Check camera menu for output assignments.
Input Not Selected
Monitor has multiple inputs. It's looking at HDMI while your cable is in SDI. Black screen. Not a cable problem.
Fix: Select the right input.
Monitoring Output vs. Recording Output
Some cameras have separate "monitoring" and "recording" SDI outputs with different capabilities. The monitoring output might be 1080p max while the recording output does 4K.
Fix: Know which output does what on your specific camera.
Power-On Sequence Issues
Some devices need to be powered on in a specific order to handshake correctly. Power on monitor, then camera, or vice versa.
Fix: Try powering everything off and on again in different sequences.
When It Actually IS the Cable
Cable problems typically manifest as:
- Consistent symptoms that follow the cable when you move it to a different setup
- Intermittent issues that correlate with cable movement
- Complete failure that isn't explained by other factors
If you've ruled out source and destination, and the problem moves with the cable, it's the cable.
The Quick Field Fix
When you find a bad cable on set:
- Replace it immediately (don't try to fix it)
- Label it "BAD" with a Sharpie
- Throw it in a separate bag/case
- Deal with it later (or never)
Your job is to get the shot, not diagnose cables.
Preventing Future Problems
- Test cables before every job
- Inspect connectors for damage regularly
- Don't exceed maximum cable lengths
- Use quality cables appropriate for your signal format
- Carry spares (at least 2 of every length you need)
The best troubleshooting is the troubleshooting you never have to do.
Stuck on a weird issue? Describe the symptoms. I've probably seen it before.
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