Test Your HDMI Troubleshooting Knowledge
Isolating the causes of HDMI problems in the field can save time and create satisfied clients. Check out these 8 real-world scenarios.
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By Jason Knott | 04.11.2012
HDMI. Never before have four simple letters caused so much pain for so many custom integrators.

When the technology was introduced back in 2002, it seemed to be the long-awaited one-wire solution to the potential rat’s nest of wiring that always hampered growth of the high-definition signal transmission in residences. And for most consumers with simple setups, HDMI has been a godsend.

But for custom installers who are often asked by clients to “break all the rules” with lengthy wire runs and multiple displays, the one-wire solution became one big headache.

At CEDIA Expo 2011, the HDMI Licensing Group held an all-day symposium to discuss “all things HDMI.” Among the hottest topics were basic and advanced troubleshooting tips, solving real-life situations in some cases. See the highlighted boxes in this article that show eight real scenarios from the AVS Forum website and their likely solutions from integrators. Use it as a fun quiz for your staff.

Also, continue to refer to our resident HDMI guru Jeff Boccaccio, who recently analyzed the inside jacket of HDMI cables.

Basic HDMI Troubleshooting Tips

Avoid the Need to Troubleshoot
Prequalify all the equipment in the home and that you procure in your lab before you start the job.

Consider the Origin of the Problem
Determine if the existing HDMI system has ever worked. If so, what changed? Take careful notes.

Make One Change at a Time
Make only one switch at a time to limit the variables. Again, take careful notes.

Simplify
Configure or “reduce” the system to the simplest configuration that still exhibits the symptom.

Substitution
Substitute suspect devices or components with known-good devices or preferably with test equipment that can emulate sources and sinks with other convenient control functions.

Disable Protocols
Disable CEC and HDCP if possible. Disabling HDCP will immediately tell you if the problem is related to that.

Diagnostic Sequence
Use the diagnostic procedure that provides greatest insight and is easiest to conduct.
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Problem 1: No Audio


Symptom: A system that consists of a DVR via HDMI to an A/V receiver (AVR) via HDMI to a projector and there is no audio?

Solution: The probable cause is that the AVR is not substituting its audio block into EDID. For the integrator, the short-term resolution is to bypass the AVR; the long-term solution is to replace the AVR.

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Problem 2: No Picture


Symptom: There is no picture following standby. The client is having a problem with his media server and HDTV. Once the TV goes to standby, the media server and HDTV will not handshake properly and he gets the infamous green screen instead of video. The only solution that works is literally unplugging the HDMI cable from the media server and re-inserting it.

Solution: The probable cause is that the media server not asserting hot plug. Replace the media server or put a “fix it” device between media server and HDTV.

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Problem 3: Intermittent Flashing


Symptom: Using HDMI for all connections, the setup is a set-top box to a DVR to an AVR to an HDTV, which results in intermittent flashing. However, when the setup is altered to DVD/Blu-ray to AVR to HDTV (all via HDMI), the flashing disappears.

Solution: The probable cause is an HDCP authentication failure. The STB is not processing the A/V receiver’s HDCP repeater bit. The resolution is to swap out STB and DVR.

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Problem 4: Pixel Errors or "Sparkles"


Symptom: Sparkles occur in the family room display from the STB.

Solution: This is the often the most difficult problem to isolate the cause. A partial list of possible causes includes:
  • Excessive dielectric loss through HDMI cable or HDMI extender or repeater device
  • Excessive skew on the TMDS pairs
  • Poor quality HDTV (poor equalization)
  • Pre-HDMI 1.3 source without pre-emphasis
There is a sequence of tests that need to be conducted to isolate the problem. First, conduct a cable/repeater test with the objective of determining if the HDMI cables to and from the matrix switch and the switch itself are passing good video. If this test passes then the most likely cause is the Extender.
Second, run a test on the Cat extender and then the Cat 5 cable itself by swapping them out. If the tests fail then you should perform individual tests on each cable. If one fails, replace it. If they do not fail, replace the matrix switch.

Third, conduct a cable/repeater test or frame test to determine if the HDMI cables to and from the matrix switch, the switch itself and the extender are passing good video. If you cannot run the cable/repeater test, then run the frame compare test.

Pixel errors or “sparkles” are caused by various things, including:
  • Intra-pair skew - The loss within one of the TMDS pairs. Typically results from differential lengths of the twisted pair
  • Dielectric loss - Distortion or “smear” of the signal due to attenuation of high frequencies
Diagnosing physical layer problems requires very expensive equipment; therefore, diagnosing such problems is by inference. The general symptom of this problem is characterized by sparkles or intermittent snow. The symptoms of some physical layer problems can be similar to HDCP protocol layer problems.



Jason Knott, Editor, CE Pro
Jason has covered low-voltage electronics as an editor since 1990. He joined EH Publishing in 2000, and before that served as publisher and editor of Security Sales, a leading magazine for the security industry. He served as chairman of the Security Industry Association’s Education Committee from 2000-2004 and sat on the board of that association from 1998-2002. He is also a former board member of the Alarm Industry Research and Educational Foundation. He is currently a member of the CEDIA Education Action Team for Electronic Systems Business. Jason graduated from the University of Southern California.