I use a channels.conf that I have created with w_scan in Ubuntu 14.04. I've done the following tests:
1) Installed vdr on a PC with Ubuntu 14.04 and using my AverMedia usb tv tuner and the application kaffeine, I was able to see tv shows. Previously I had to build the media_build from linuxtv.org. This way I know that lastest linux drivers work.
2) As I said before, I have tested another raspberry software that uses XBMC as frontend and installed vdr as backend called OpenElec. It work, I was able to see channels without any problem with my usb tv tuner. I used the channels.conf created with Ubuntu.
3) Using another SD card I installed MLD and did not work.
I'm using a Rapberry Pi B+, with a 2A power supply and inserting the USB tv tuner directly to the RPI. I have also tested connecting the tv tuner through a USB hub.
The signal quality if good, because if I change the SD card and put the OpenElec software it works. If then, usign the same hardware I put the SD card with MLD it does not work.
I was not able to use w_scan to get channels.conf in MLD because I have the following problem:
MLD> w_scan -c ES -a 0
w_scan version 20120605 (compiled for DVB API 5.4)
using settings for SPAIN
DVB aerial
DVB-T Europe
scan type TERRESTRIAL, channellist 4
output format vdr-1.6
WARNING: could not guess your codepage. Falling back to 'UTF-8'
output charset 'UTF-8', use -C <charset> to override
main:3225: FATAL: failed to open '/dev/dvb/adapter0/frontend0': 19 No such device
MLD> ls -l /dev/dvb/adapter0/frontend0
crw-rw---T 1 root video 212, 3 Dec 5 22:51 /dev/dvb/adapter0/frontend0
I do not know why it says "No such device", because the device node exists.
Last week I was looking at the MLD logs and saw an error message from udev related to not being able to start something called net.agent. Maybe it makes udev not finish properly. IMHO I think there must be something wrong in MLD kernel or udev, or whatever... that makes the AverMedia driver not work.
I will try to investigate more later, but if you have any suggestion it will be wellcome.
Jordi