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Old 02-11-11, 07:49 PM   #1
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Join Date: Feb 2011
Posts: 11
Default LG TV no video when no audio; when audio active, video works

I have an LG TV (37LD450) that I've just started using with MythTV as a secondary TV. The primary TV is a Panasonic that is working fine. The Myth PC has one HDMI output that I have split to the two TVs. I can see the Ubuntu desktop just fine with the Panasonic and can start MythTV and play a recording. But on the LG, there's no video display at all ("no signal") until the recording starts. And when the recording ends, the LG drops the connection again. I can show the same behavior in Firefox where I can pull up Hulu, hit play, the video shows on the LG, then I navigate to another page, and the LG drops the connection again. Even the simple speaker-test will turn on the LG until I end the test and the LG drops the connection.

(Before anyone asks, yes, I'm sure about it all. I've tested everything imaginable. The LG TV works fine with the Comcast cable box in the same setup - if I just pull the HDMI from the Myth box and plug it into the Comcast box, both TVs work fine. Also, if I plug my Win7 laptop into the chain, both TVs work fine. And there's no difference if I just run the cable directly from the Myth box to the LG TV. And yes, I've tried all sorts of different cables.)

The LG tech came today and confirmed the TV is working as LG says it should. And there is no service menu option for changing the behavior. Also, there is no firmware upgrade for my TV. I've found numerous other complaints on the net about LG TVs not working with MythTV and other linux installs.

In desperation today, I clicked on Ubuntu's System Additional Drivers and tried switching to the previous version (the one not recommended; "176", I think?). Surprisingly, the problem went away and the video immediately showed on the LG without needing any audio playing at all. Except then the video playback was broken - it went to black screen whenever I tried video in MythTV.

I then blew away all the drivers that come with Ubuntu and installed the latest released version from NVidia's site and returned to the working video only when audio was in use problem. In fact, all the 4 versions I tried from Nvidia's site all had the same result. Except when I dug too far back, then the driver didn't work at all and there was no display on any TV.

So I'm settling into the following conclusion: The NVidia driver needs to be fairly recent to get the video working. But the recent versions of the driver don't have the the audio active on the HDMI until an application needs it. That might be efficient somehow and it doesn't seem to matter for most displays. But for who knows what reason, it matters to the current crop of LG TVs.

I've considered trying to find away to get some sort of audio signal kicked off on startup and have it linger in a pause state or a silent active state for the duration of the ontime. But before I even figured out how I might do that, I realized that if one application has the audio in use, another application can't use it.

Therefore, the only way it seems I'll be able to use the TV with Ubuntu (and my MythTV install) is if I can somehow get the Nvidia driver to activate the audio connection on the HDMI port at all times. If anyone knows of a setting somewhere, I'd love to know about it! Or if anyone has other theories, I'd love to hear about that too. And if there's any chance to influence future driver implementations, that'd be great too. I'm up for testing anything!!

Thanks for any suggestions!
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