[mythtv-users] Mythtv can't tune one channel tunable using tzap+mplayer

[Ian Peake]

[Apologies if a similar message is posted later.. my first mail was
from a not-subscribed
alias address and has been held for moderation and/or dropped for several days.]

I have ongoing problems with mythtv tuning just one particular multiplex
("SBS") which tunes passably using tzap+mplayer.

Can someone suggest next steps to tracking down this problem?
See backend log at http://pastebin.ca/828312 and further details below.

The problem is quite reproducable on my setup:
Mythfrontend OSD always gives "LMs" (partial SDT) with signal of approx 58% but
no better, i.e.: no picture or sound. I can tune with tzap_mplayer.

Mythtv is a recent Debian build 0.20.2.svn20071210-0.0 and several earlier
versions.

I am using a Hauppauge Nova-T 500 with very recent
v4l-dvb subsystem (from mercury repo sources),
I have tried patching with the Hauppauge "reception patch"
http://www.linuxtv.org/pipermail/linux-dvb/2007-August/019493.html
I have also enabled the low noise amplifier (force_lna_activation=1).

Admittedly reception seems only marginal to fair
(approx. 20m connection to old outdoor antenna),
however I can adequately tune all channels apart from SBS
in mythtv. (That is, about four other multiplexes over a combination of HD/SD.)
I can also tune all channels using an STB on the same antenna.

Moreover, tzap+mplayer works for all multiplexes/channels,
and seemingly on both tuners.
The one odd thing is that tzap reports a SNR of 0. I have seen
that reported elsewhere for the Nova-T 500 but not any
solution or explanation.
Admittedly signal quality (BER metric) seems quite variable
rapidly while using tzap.

A similar problem described at
http://www.gossamer-threads.com/lists/mythtv/users/278168#278168
was solved by manually adding 166667 to the frequency of the
multiplex.  That doesn't seem to work for me.
It wouldn't surprise me if I somehow corrupted mythconverg tables
but as far as I can interpret the diagnostics and log
myth is at least getting a lock.

tzap "SBS" shows..

using '/dev/dvb/adapter0/frontend0' and '/dev/dvb/adapter0/demux0'
tuning to 536625000 Hz
video pid 0x00a1, audio pid 0x0051
status 07 | signal 9748 | snr 0000 | ber 001fffff | unc 00000035 |
status 1f | signal 978f | snr 0000 | ber 00000000 | unc 000000d8 | FE_HAS_LOCK
status 1f | signal 97c8 | snr 0000 | ber 00000000 | unc 00000000 | FE_HAS_LOCK
status 1f | signal 9765 | snr 0000 | ber 00000000 | unc 00000000 | FE_HAS_LOCK
..

When I first started using mythtv approx September, with an older
version, for a few
weeks I recall that I could tune SBS even with very poor reception
from an indoor antenna.
I haven't tried replicating that but I have tried adding an attenuator
to the antenna cable path, with no apparent improvements.

Kind regards,

Ian Peake