[mythtv-users] LiveTV access was working, somehow I stopped it working

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Greetings mythizens

I would love to hear some ideas about how to fix this.
I don't _need_ LiveTV but it is handy to have.
Planning to upgrade to v30 but it's not an option for a few weeks.

I installed a new card [1] in my system today [2].
I left an existing card [3] in place.
I rearranged the antenna connection so that there was a splitter
plugged into the new card, with the antenna connection on one side
and the existing card on the other.

After stopping the backend, running mythtv-setup (deleted all tuners
and added them back, setup input connections, etc) and then restarting
the backend and running mythfilldatabase;
I started the frontend and tried to check things by starting live TV.

At first, everything was fine, using the new card's tuners.
Then I used the on-screen menu to change the Live TV source to be
one of the existing card's tuners. This worked but showed that the
card was struggling a bit for adequate signal.

At this point I exited Live TV (did not switch the LiveTV source
back to one of the new card tuners) and started rearranging coax
to try and provide a bit more signal to the older, existing card.
The issue I hit was that I could no longer start Live TV.
I would press 'ok' on the LiveTV menu item and get a 'please wait'
popup for less than a second, then back to the main menu.
In the backend log I found this being logged on each attempt:

 mythbackend[5126]: I TVRecEvent tv_rec.cpp:1090 (HandleStateChange) TVRec[1]: Changing from None to WatchingLiveTV
 mythbackend[5126]: I TVRecEvent tv_rec.cpp:3665 (TuningFrequency) TVRec[1]: TuningFrequency
 mythbackend[5126]: W TVRecEvent dtvmultiplex.cpp:315 (ParseDVB_T2) DTVMux: Invalid T2 modulation system parameter  '', aborting.
 mythbackend[5126]: E TVRecEvent recorders/dtvchannel.cpp:300 (SetChannelByString) DTVChan[1](/dev/dvb/adapter0/frontend0): SetChannelByString(10): Failed to initialize multiplex options
 mythbackend[5126]: E TVRecEvent tv_rec.cpp:3743 (TuningFrequency) TVRec[1]: Failed to set channel to 10. Reverting to kState_None
 mythbackend[5126]: I TVRecEvent tv_rec.cpp:1090 (HandleStateChange) TVRec[1]: Changing from WatchingLiveTV to None

After trying several things, I still cannot get Live TV working.
I think what has happened is myth has saved the Live TV input as
one which doesn't really have enough signal, but I'm not sure.
I don't see any way to tell what tuner LiveTV is trying or any
way to control which one it initially tries.

Things I have tried, to no avail
 - delete channel "10" with the mythtweb channel editor
 - the new card tuners were configured to start at channel number 7,
   while the older ones were configured to start at channel 10.
   Change the initial channel for live tv from 10 to 7.
 - delete all tuners, add back only the new card ones,
   connect inputs as before. (the old card is still installed)
 - reboot

Recordings (with just the new card's tuners) seem to be working fine.
Have not tried scheduled recording with the old card's tuners.

Kind Regards to all for 2020

Footnotes
[1] PCI-E HauppageTV-QuadHD (PCI ID 0700:6a28).
[2] v29, running on ubuntu LTS 16.04 amd64, combined fe/be
32] PCI Dvico FusionHDTV DVB-T Dual Digital 4 (USB ID 0413:6a05)