I am new to the forum and signed up to thoroughly document a problem I recently had with my Sony KDL-55NX810 that is setup with the SU-B550S Monolithic Stand where the stand quits working altogether.
Originally when this happened I researched the problem online and was unable to find any documentation on any forums anywhere about the SU-B550S not turning on and not allowing HDMI signal passthrough. Even though I had read the instruction manual I didn't see anything that I thought to be helpful in troubleshooting this problem so I contacted Sony Customer Service and explained the problem. Their solution was to try plugging the unit into a different wall socket to see if it would turn on. To my surprise they had little knowledge of the stand and asked me if the power switch was on even though the stand does not have a power switch as it is controlled by the TV through the HDMI ARC (Audio Relay Channel) port.
What I did notice is that when I would unplug and plug in the unit I would get HDMI signal passthrough for approximately 7 seconds before the picture would just go black and the TV would report signal not found.
I fought with customer service to see if they would send out an in home repair technician to evaluate and possibly repair the unit and they flat out refused even though both the stand and TV are still under the original factory warranty.
It isn't exactly easy to mount and dismount the television from the stand but they said they wouldn't send someone out since it is just an accessory. They told me that if it I didn't have the original stand I should place the TV on the floor while shipping out the stand for evaluation by their service techs. To me this was completely unacceptable. Even after I gave in and asked how the return process would work they told me they would only send a label, not a proper return box regardless of the unusual shape and size of the stand. So I gave up temporarily...
I ordered a brand new stand thinking I would replace it and easily solve my problem. Then I would have the official box that it fits in and it would be easy to ship back with a return label. Once fixed I could simply keep the fixed/replaced unit or sell it. Easy right?
When I got the replacement stand I took down the TV and switched out the stands, hooked everything back up and the new stand didn't work. At this point I started to suspect the TV was at fault. Usually in this type of situation I would simply evaluate anything I might of changed in settings, hooked up recently, or added to my setup and nothing was apparent. Quickly I requested an RMA for the new stand and decided I would return it to Sony for a refund. At this point I suspected the TV itself and felt I could now provide documentation of what I had done to Sony Customer Service which would better illustrate the problem being with the TV itself. Hopefully this would get them to agree to an in home repair technician.
At this point I put the old stand back and just for the sake of trying I went through the setup process one more time and it started working suddenly. Then I realized that the Mini Display Port to HDMI cable I use for my MacBook Pro wasn't plugged into the TV, I missed it when plugging everything in. So I plugged it in and after 7 seconds the stand shut down!! I unplugged it and the picture returned but without sound. I repeatedly plugged and unplugged to be sure this cable was the culprit. After unplugging the cable a simple power cycle on the TV would turn the stand on and restore sound.
I had forgotten I had recently added the cable to the TV replacing an old VGA connector and it was the last thing I used before discovering the problem several days later. When using the Mini Display Port to HDMI cable I wasn't using sound on the computer so I didn't realize the bar wasn't working. The reason the picture didn't go out was because the Mini Display Port to HDMI cable was connected directly to the TV instead of the HDMI passthrough on the stand.
And then it hit me, I remembered reading in the Instruction Manual a single line saying "Do not use PC with HDMI." So it was there all along but with no other detail so not very apparent. Maybe a poor translation from the original Japanese documentation? Who knows...
Since then I have quit using the cable to avoid the problem. One reason I speculate that the cable caused interference is that the Cable contains a chip between the Mini Display Port and HDMI ends that translates the signal into an HDMI ready output that passes the necessary handshake the TV requires to display the signal. This chip receives it's power from the HDMI port itself so the TV recognizes it as connected even if there isn't a computer connected to the other end sending the Mini Display Port signal. I imagine the chip emits a static signal that interferes with the operation of the ARC signal being transmitted to the bar allowing for it's management by the TV. It appears that even though I had it plugged into HDMI 4 and the ARC runs through HDMI 1 that in the end all of the HDMI ports are linked together on the same receiver board so the signal still interferes.
My hope is that documenting this will help anyone else who might experience this problem. I really hate when stuff quits working unexpectedly and wish that my first call to Sony Customer Service would have had them better evaluate the problem by asking me if I had any PC or PC related cable connected to the TV. They should have better troubleshooting information of their products in both their Instruction Manual and with their Customer Service Reps.
One last note, before writing this I tried to find similar problems related to the ARC functionality as it is found across many TV manufacturers and still I came up empty handed. I can't imagine I am only person that has seen this problem. Maybe other manufacturers have better troubleshooting and warnings outlined for customers in the Instruction Manuals they provide with their products?