This issue unfortunately still exists.  I think it's isolated to W7 64bit though as I just built up a new machine (w7-sp1 all updates, latest drivers, Avermedia Duet and a Sandy Bridge CPU) and have this problem.  With my previous machine and W7 32bit and the exact tuner card, I had no problems recording 2 things at once, watching live TV etc.

It's so annoying that I might just rebuild with W7 32bit.

I installed W7 pro 64 on 3/20/11  and WMC worked fine for 9 months until 12/05/11 when I started getting <<No TV Signal>> or <<Low Bit Rate>>.  Image, sound and blue screen msg alternate at 5-30 seconds interval.  On a clean restart WMC will run clean for about 15 minutes.

I have:

Vaio VGN FW351G

Intel Graphic chip

Hauppauge WinTV HVR 950Q (2 of then with same issue) hooked to cable and using analog and clear QUAM

Win7 is up to date, WMC is up to date and I have the latest drivers from Hauppauge, Intel

KB9981129/30 did not fix the problem

Turning off the graphic manager did nothing.

Running Troubleshooter "Set TV Signal" found no issues.

I am really at a loss to understand why WMC would stop working out of the blue.

I had this problem on a few cards, took me about 6 weeks to work it out. I found my ATI HD 4850 was the cause, it was having IRQ conflicts with the High Definition Sound  (on board), when I disabled the HD sound the IRQ jumped from 17 to 22 and the tv tuner ran smoothly until I rebooted and the same issue was happening, there is a few ways to solve this one being turn your PC into a standard PC rather than a ACPI Computer or (what I did) change the graphics card to an Nvidia 8400gc fanless card and move the tuner card up one slot on my motherboard, reinstall software and hey presto. I've had a few ATI cards which conflict their IRQs so this is why I went down the Nvidia route.

Dazza,

I didn't think of looking for hardware conflict... for now, I got a hold of an ATI TV Wonder 750, and I get a stutter on WMC (video and audio) but can get a steady picture and audio using TotalMedia. Either the signal is just fine or the Hauppauge tuner is more sensitive but then why would it work for 9 months before failling? At some point I will put back the WinTV HVR950Q and check for hardware conflics.  Both tuners lack a hardware encoder for analog chanels, that function is performed by the cpu with the help of the gpu on Win7.  On my system that means the cpu is about 20% busy, that's a great improvement over Vista with no GPU encoder support with 80% + cpu busy and a severe case of stutter on video and audio.  I have not looked for GPU usage to see if it is overwelmed with mpeg encoding of the analog channel, I'll look for tools that might tell me.

Try this:

In the Guide, right-click the channel name, and edit the channel. Then, go into the channel sources.

Windows 7 Media Center (MC) sometimes has a tendency to add redundant sources for channels. These duplicate sources wreak havoc on the tuner logic, and you often run into these No Signal errors (although usually, 7MC recovers and is able to start recording from another free tuner).

Go through the sources. If you find the same tuner listed twice, disable one of the listings. Also, disable any tuner sources that may be invalid (i.e. MC says you can tune via ATSC, but you really can't).

Source: answers.microsoft.com/.../4c7b08b4-533d-4924-b3fd-f1415e0b1c25

Alex,

Thanks for the suggestion, I came across that before and all channels had a single source.

One web site sugested to use dpclat.exe (from http://thesycon.de) to check if a device driver was causing too much latency on the dpc queue interfering with smooth rendering of audio/video.  I did find that the WiFi device was causing spikes every 7-8 seconds on my system so I disabled the WiFi device. Voila (almost) I now get smooth audio/video with the ATI tuner with WMC BUT if I stop dpclat.exe, I get a jerky rendering.

Encouraged by the ATI tuner results, I went back to the Hauppauge HVR 950Q tuner because the analog channel image quality is much better (they have an excelent de-interlace filter).  With the Hauppauge WinTV program, the results are better.  I no longer get the 'No signal' message but the rendering has long pauses from 2-10 seconds: unusable! I got the same result with or without dcplat.exe running unlike the ATI tuner, all the gain was from disabling the WiFi device.  

I then tested the HVR 950Q with WMC.  The first good news was that a bunch of unencoded QAM channels were detected again when I ran the WMC TV Setup  (it was setup for the ATI tuner so I had to run Setup for HVR 950Q). All those unencoded QAM channels had dissapeared on previous setups. Unfortunately I got the same15 minutes of initial smooth video then it got jerky and the 'No TV Signal' message reappeared but not the "Low Bit Rate" message.  WMC recovers from that but this is no way to watch TV.

Dpclat.exe was interesting in a number of ways: 1) it allowed me to detect the WiFi spike 2) it clearly showed that the HVR 950Q causes double the latency that the ATI tuner incurs (because of better de-interlace filter??) 3) it also showed that QAM channels don't incur any detectable additional latency on dpc 4) when it's not running WMC is jerky with the ATI tuner.

Although dpclat took me on an interesting journey,  I am still no closer to finding the cause or solution to my problem.  I thought that playing a QAM channel would stop the behavior since it incurs no detectable latency on dpc but no such luck. Even while playing a QAM channel I got the 'No TV Signal'.

I'm not giving up, I'll nail it...

I think I used Sysinternals Process Explorer for DPC, it's pretty good, shows which process causes the latency.