Diagnosing intermittent AV dropouts: ground loops, CEC and power noise

Why intermittent dropouts are hard to diagnose

Intermittent dropouts are hard to diagnose because they don’t often leave clues. In many cases, they may be fully functional for days before failing. Rather than hardware, intermittent dropouts are caused by environmental or electrical problems.

The combination of AV ranks, power distribution and HDMIs from mixed vendors makes it even more complex. As integrators, we should eliminate causes – not guess. To find the cause, it’s essential to understand grounding, CECs (Consumer Electronics Control) and power noise.

Ground loops: a silent destroyer of signal stability

Ground loop issues are linked to grounding paths – a safe path for electricity to return to the earth. When two devices share multiple paths, there may be unwanted current travelling along audio, video or HDMI shields.

It’s identifiable through symptoms such as:

• Audio systems emitting a low-frequency hum
• Signal loss or flickering in videos
• Dropouts when a device is switched on or off

Thankfully, there are ways to fix ground loop issues. You should check the grounding before replacing hardware, as failures often start with grounding:

1. Share a single electrical circuit for all AV components, where possible
2. Choose high-quality shielded cables with proper rack grounding
3. Where needed, add isolation transformers for audio or cable TV feeds
4.  Remove legacy connections like splitters and coax lines.

HDMI-CEC conflicts: when ‘smart’ control causes chaos

While customers enjoy the autonomy of CED, it does mean that devices can control each other. When brands are mixed, it causes looping commands, power cycling or input switching. This can manifest as:

• Screens suddenly turning off
• Sources switching inputs by themselves
• Lost sync or muted audio for AVR

These loops are particularly common in HDMI chains with switchers or matrix systems. To fix them, start by disabling CEC on devices where it’s not needed. Ideally, all brands should be standardised so we can predict their behaviour. To automate functions, choose control processors rather than CED.

Power noise and EMI: hidden interference sources

Unwanted electrical interference can affect sensitive AV equipment. The source may be high-power appliances, dimmers, HVAC units or even LED drivers. This may be the cause if you spot:

• Dropouts at the same time that dimmers or motors start
• Unstable Wi-Fi near power supplies
• ARC failures or unpredictable HDMI handshakes

Fixes for power noise and EMI include:

1. Using a line analyser to verify clean power
2. Adding power conditioning or Uninterruptible Power Supplies for central racks
3. Separating mains wiring paths, choosing low-voltage alternatives
4. Replacing low-quality power adapters if they leak noise.

Remember to diagnose by elimination. If the dropout coincides with electrical activity, it’s likely an EMI issue.

Recommended troubleshooting workflow

If you’re not sure where the source of the dropout is, try the following diagnostic process:

1. Replicate the dropout in another location
2. Isolate grounding paths to detect ground loop issues
3. Disable any CECs and test again
4. Check power outlets for EMI.

You should replace or re-route only after you’ve ruled out electrical causes.