How I solved HDMI ARC problem between a set-top box, TV and Sonos arc using scissors.
This hack is the best I ever conjured up. Could it be a Halloween effect? 👻🎃👻
Problem
Recently we had problem connecting soundbar (Sonos Arc)to TV (LG OLED55B6T). The problem observed was that the Audio output through HDMI ARC (Audio Return Channel) was not stable. When only HDMI ARC port (HDMI2 in my case)was in use on the TV connected to soundbar everything worked correctly. In this mode the content was limited to Streaming sources such as Netflix, Amazon Prime, YouTube etc. The moment any other HDMI port on the TV was connected audio stopped working. To get it back to working I had to shutdown the TV completely, remove all other HDMI cables other than ARC port and then restart the TV. This was a serious problem since I also had a set-top box and PC using TV as their display devices connected through HDMI ports. The solution I wanted was all content sources to play nice and route respective audio signal to soundbar with TV working as the controller. In this post I am outlining cause of this problem, possible solutions and how I solved it satisfactorily at zero additional cost.
Debugging
Problem required extensive debugging. At the end of it it was clear to me that sound stayed stable as long as my set-top box was not connected to TV through HDMI. This conclusion ruled out TV, soundbar as well as quality of HDMI cables as possible causes of the problem. My Set-top box was NXT HD from DishTV India. Diving deeper into the HDMI connector protocols it appeared that implementation of Consumer Electronic Control (CEC) protocol on the set-top box could cause instability in multi device connection environments. At this point I spent sometime looking for ways to turn off CEC from either TV or set-top box. Unfortunately in my case turning off CEC was not possible through software interfaces.
Engineering a solution.
I started looking for hardware solutions. There were many hardware solutions in the market to disable CEC on HDMI. All of them used a simple adapter that ‘magically’ disabled CEC — a protocol implemented from ancient days of HDMI. In fact CEC became a standard from 2005 along with HDMI 1.3 implementation. So it was impressive to see that a small piece of hardware could disable CEC without losing other goodies of HDMI. This intrigued me to understand how these nifty devices were disabling CEC.
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To detect CEC support and to communicate between devices, HDMI protocol uses a single wire. Specifically PIN 13 on an HDMI connector carries all information. When you are holding an HDMI cable in front of you with the wider side at top, PIN 13 is the 4th pin on top from right end.
So I deduced, it is likely that these CEC-less adapters are doing nothing more than breaking the CEC connectivity on PIN 13 on an HDMI cable. Simple enough.
With this knowledge at my disposal many DIY solutions were possible.
- Could make a DIY HDMI cable — not really possible for me, especially since I am one of those mechanical engineers who royally flunked basic electronics. Could not solder to save my life!
- Pry out PIN 13 from one end of the connector. This fit perfectly in my alley. Tried hard to do it with a pair of tweezers and many other such mechanical solutions. Was not easy!
- Just mask PIN 13 with an electrical insulation tape. This thought sounded ridiculous at first. Many things could go wrong — I could block the wrong pin, the insulation could bung up and disable by HDMI port etc. But I decided to give it a try.
Solution
Cut an insulation tape thin enough to cover a PIN. Used a magnification glass and pair of tweezers to carefully mask PIN#13. Left enough of tape outside — in case need to pull it out later.
Now it was the moment of truth. A quick test with a computer monitor and PC showed display data was flowing w/o any problem. So I used this cable to connect TV and the set-top box.
Audio worked flawlessly. No more audio dropouts. CEC completely disabled for the set-top box. Switching TV off and powering it back on settings stayed. Pure surround sound from HD channels also filled our media room!
Final thoughts
- If you are inclined to try this hack — you are on your own. It worked for me. It could be my dexterity, dumb luck or both. You may lack either or both. All the best!
- DishTV — please add a software setting to disable CEC. It helps!
- LG and LG WebOS people — Please decouple CEC (what you call Simplink) and HDMI ARC. It should still be possible to use HDMI ARC w/o using CEC.
- People who are trying this solution be very careful to not mask PIN NO 15. Pin 15 is the third top pin from the right. Use the pinout diagram above to confirm its location. Pin 15 carries Display capability information. By masking that pin accidentally you may observe your HD resolution dropping to 720p. It happens because the set-top was unable to correctly identify max display resolution of your TV.
- Debugging problem to CEC fault on set-top box was not as simple as I made it sound. It required visits from LG and Sonos support people. One of them identified problem as dishtv’s CEC implementation by trial and error. I am no Sherlock Holmes!
- Solution came to me on Oct 31st. Solution was to block Pin #13. Now, that is either some coincidence or…👻🎃👻
