[mythtv-users] HD-PVR strange behavior - solved!

Will Dormann wdormann at gmail.com
Thu Jun 6 04:10:49 UTC 2019

Hi folks,

I've got a strangely-behaving HD-PVR 1212 where I haven't been able to
pinpoint the problem (until just recently, and I'm sharing this story in
case it helps anybody else here).  The symptoms are:  When I turn my A/V
equipment (TV, HDMI Audio receiver) on or off, the HD-PVR stops recording.

The simplest test is to run:
cat /dev/video0 > /dev/null

The light on the front will turn red to indicate recording.

At this point, if I turn on *or* off my TV *or* my AV receiver, the red
recording light on the front of the HD-PVR goes off.  The cat
/dev/video0 process isn't interrupted, and there's no indication of any
trouble in kern.log.

Things I've tried to no avail:
- Wall wart PSU for the HD-PVR rather than the 5V-rail cable coming from
my PSU (I'd heard enough horror stories about the wall warts dying, so I
figured I'd preemptively set mine up this way).
- Different USB cable
- Different USB port on the PC
- Different power outlets for the various components
- Different Component Video cables

Just as I was about to give up and ask for advice here, I figured out
the problem!

My cable box (from Verizon FiOS) has both HDMI output going to the AV
receiver *and* component output going to the HD-PVR.  The purpose here
was in case I had the very-rare occasion where I'd want to bypass the
entire MythTV system to see the output directly from the cable box. The
symptoms I noticed were that if I turned on the AV equipment while an
HD-PVR recording was going on, I'd notice the red light on the box go
off for a couple seconds, and eventually recover.  The recordings were
mostly OK, except for a drop-out around the time that the light went
off.  In some cases, the corrupt video was enough to crash mythfrontend!

Anyway, as a last resort I tried unplugging the HDMI cable from the
cable box.  Bingo!  No amount of turning the receiver and/or TV on/off
would interrupt the HD-PVR recording!

Theory: When an interconnected HDMI device (TV or AV receiver) is power
cycled, it sends some sort of signal (or glitch?) along the HDMI "bus".
Since the cable box is connected via HDMI to the AV receiver, this
signal makes its way to the cable box.  At which point, the component
video output is temporarily glitched.  The HD-PVR apparently doesn't
like this.  If you're currently doing a cat /dev/video0, this never
recovers.  MythTV appears to notice trouble and restarts the video
recording when trouble is encountered.

It's a long shot, but I suppose that if you've noticed that your HD-PVR
occasionally stops recording temporarily when power cycling any
HDMI-connected components, check to ensure that the HD-PVR is the *only*
thing connected to your video source.


More information about the mythtv-users mailing list