I have an HDHomeRun; originally I installed the software on Windows, then I took the time to configure Myth. I was left with 2 channels that Windows can tune every time, but Myth can never get a lock. I am connected to Comcast Cable in SE Pennsylvania. Here are the steps I took to fix this. I hope someone else can benefit. I also hope someone can streamline the process.

I'll eliminate suspense up front by saying that the problem was that during detection, even though the channels were detected correctly, the wrong tuning information was stored in the database. I'll also caveat this by saying everything I know about QAM-256 tuning I learned working on this problem, so there may be errors, by "may be" I mean "very probably are"


I installed in myth following the instructions on Ubuntu's Website which is where the SiliconDust website pointed me.

All was joy except for two channels, both local broadcast stations, so I expect them to be unencrypted and available. I noticed that the "freqid" for all other stations matched the "Channel" that that HDHomeRun Setup in Windows had EXCEPT for the two bad channels. The first was channel 29.1, Windows says it is CH111-2, myth says the freqid is 114. So I changed the freqid in MythWeb to 111, and tried again.
No Luck.

It turns out that the problem is a little deeper. There is another column in the channels table that is NOT displayed on the Channel Editor page in MythWeb, I didn't see it on the ChannelEditor in mythtv-setup either (although I may not have looked hard enough.) the column in question is "mplexid"
This is still not exactly what we're looking for but is a pointer to what we want. It refers to the dtv_multiplex table. which I'll get to later.

Here's what to to:
1. Go to the Windows box, and run HDHomeRun Setup, Select Lineup, and Edit. The Channel Editor Window pops up.
2. Find the channel that misbehaves in Myth, and select "View". Ignore the video window, but don't close it. In my case I'm looking at CH111-2
3. Start HDHomeRun Config. Select the "device" that you are viewing.
4. In the "Status" section, make note of the Physical Channel, in my case "qam256:717000000"
5. Close out Windows; you're done with it.
6. Now on the mythbox get to a commandline by your favorite route.
7. get into mysql
>mysql --user=mythtv --password mythconverg
8. find your mplexid using the part of the physical channel after the colon

So in my case I'm interested in mplexid 31.
9. Now let's look at that bad channel again:

10. finally the fix:
Note the chanid, this is the table key.

11. repeat the process for all channels that are effected.
12. I rebooted, but restarting the backend should be sufficient to make the change take effect.

Enjoy.