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DVBSigMon errors

Posted: Thu Feb 01, 2018 8:02 pm
by jl6tv
Hi, I'm hoping someone can help me diagnose the following issue. I'm running MythTV 0.28 on Ubuntu 16.04 - default packages and as close to default settings as I can manage. My tuner is a PCTV 292e. I am in the UK, trying to receive Freeview. I can successfully scan for channels - everything is detected, including HD channels.

But when I start Mythfrontend and select Watch TV, I am told "No Lock", "Signal 0%", and after 3000ms, I get a message telling me I should have received a channel lock by now. Taking a look at the mythbackend log, I see the following:

Code: Select all

2018-02-01 19:53:36.743988 W  DVBSigMon[1](/dev/dvb/adapter0/frontend0): Cannot measure Signal Strength
			eno: Operation not supported (95)
2018-02-01 19:53:36.744107 E  DVBChan[1](/dev/dvb/adapter0/frontend0): Getting Frontend signal/noise ratio failed.
			eno: Operation not supported (95)
2018-02-01 19:53:36.744113 W  DVBSigMon[1](/dev/dvb/adapter0/frontend0): Cannot measure S/N
			eno: Operation not supported (95)
2018-02-01 19:53:36.744222 E  DVBChan[1](/dev/dvb/adapter0/frontend0): Getting Frontend signal error rate failed.
			eno: Operation not supported (95)
2018-02-01 19:53:36.744230 W  DVBSigMon[1](/dev/dvb/adapter0/frontend0): Cannot measure Bit Error Rate
			eno: Operation not supported (95)
2018-02-01 19:53:36.744338 E  DVBChan[1](/dev/dvb/adapter0/frontend0): Getting Frontend uncorrected block count failed.
			eno: Operation not supported (95)
2018-02-01 19:53:36.744343 W  DVBSigMon[1](/dev/dvb/adapter0/frontend0): Cannot count Uncorrected Blocks
			eno: Operation not supported (95)
2018-02-01 19:53:39.842045 W  TVRec[1]: TuningSignalCheck: taking more than 3000 ms to get a lock. marking this recording as 'Failing'.
2018-02-01 19:53:39.842065 W  TVRec[1]: See 'Tuning timeout' in mythtv-setup for this input
My attempts at googling keywords led me to one post on the mythtv-users mailing list from 2015, but it had no responses.

I am convinced my TV tuner hardware works, as I've managed to use it successfully on Windows 10 using the supplied TVCenter software.

How should I proceed?

Re: DVBSigMon errors

Posted: Fri Feb 02, 2018 8:56 am
by MikeB2013
The "...eno: Operation not supported (95)" messages are not necessarily of concern - they may just be information messages, just depends on the specific driver for your tuner.

There are a few other things to check/change first.

1. Often for DVB-T/T2 the timeouts in Capture Cards of 1000 and 3000 are too low, suggest you change to 7000 and 10000 respectively, using mythtv-setup. Make sure mythbackend is not running before starting mythtv-setup by doing "sudo systemctl stop mythtv-backend.service" from a terminal.

2. It is possible that mythbackend is starting before your tuner(s) have fully initialised - this is a fairly common problem, particularly with fast disks. There is a simple test you can run to see if this is the problem:

Reboot your system, check if you can tune, if not, from a terminal session run "sudo systemctl restart mythtv-backend.service" if the issue goes away mythbackend is starting too quickly. There are many possible solutions to this, depending on your specific hardware configuration (motherboard, tuners devices, type of disks, network etc.). A general, pragmatic, solution is to delay mythbackend startup on boot - I use 20 seconds which should be plenty :

"sudo systemctl edit mythtv-backend.service" and then add the following two lines:

ExecStartPre=/bin/sleep 20

Then exit from the edit screen (it uses nano by default, so Ctrl+x, then
y, then Return key) then reboot the machine.

EDIT: The above fix also resolves the problem with networking e.g. mythbackend starting before networking has been fully established.

If none of the above resolves your issue, please provide full mythbackend log (/var/log/mythtv/mythbackend.log) and output from dmesg command (e.g. dmesg >dmesg.log). These files if not too large can be attached to a post, otherwise pastebin and post the pastebin references.


Re: DVBSigMon errors

Posted: Mon Feb 05, 2018 5:05 pm
by jl6tv
Hi Mike,

Thanks for your offer of help. I have set the timeouts to 7000 and 10000 as you suggest. Unfortunately it hasn't made any difference. I've also made sure to stop the mythbackend service and start it manually in a window, so that I can be sure it's starting up well after tuner initialisation. Again, hasn't helped.

Here is my mythbackend log, copied from the terminal window in which I manually started the backend:

Here is my mythfrontend log:

Here is the output of dmesg:

The forum software prevents me from pasting the full pastebin URL.

Re: DVBSigMon errors

Posted: Tue Feb 06, 2018 7:13 am
by MikeB2013
Thanks for the pastebin information. The captures from a terminal window are not the best, the real logs contain different information.

From the mythbackend log:
1. Your mythtv version: fixes/0.28 [v0.28-2-g15cf421] is very,very old (Ubuntu repositories are often out of date for mythtv)
2. The mythbackend is being started in a terminal by user taylor, this is not recommended
3. There seems to be a problem with Storage Groups, writing to /home/taylor/1101_20180205164935.ts is strange!

For 1.

You need to update mythtv to the latest version of fixes/0.28 by doing the following in a terminal
sudo apt-add-repository ppa:mythbuntu/0.28
sudo apt update
sudo apt upgrade
sudo reboot

For 2.

mythbackend should be started, stopped or restarted as follows in a terminal:

sudo systemctl start mythtv-backend.service
sudo systemctl stop mythtv-backend.service
sudo systemctl restart mythtv-backend.service

Note mythbackend is automatically started on boot by systemd.

For 3.

You need to setup a default Storage Group as a minimum, typically /var/lib/mythtv/recordings/ for a simple installation. Mythtv 0.28 when installed creates a number of Storage Group directories which are as follows, the ownership and permissions are critical for correct mythtv operation.

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mike@xubuntu-1604:~$ ll /var/lib/mythtv/
total 48
drwxr-xr-x 12 root   root   4096 Feb  5 17:59 ./
drwxr-xr-x 78 root   root   4096 Feb  5 17:59 ../
drwxrwsr-x  2 mythtv mythtv 4096 Jul  5  2017 banners/
drwxrwsr-x  2 mythtv mythtv 4096 Jul  5  2017 coverart/
drwxrwsr-x  2 mythtv mythtv 4096 Jul  5  2017 db_backups/
drwxrwsr-x  2 mythtv mythtv 4096 Jul  5  2017 fanart/
drwxrwsr-x  2 mythtv mythtv 4096 Jul  5  2017 livetv/
drwxrwsr-x  2 mythtv mythtv 4096 Feb  6 06:50 recordings/
drwxrwsr-x  2 mythtv mythtv 4096 Jul  5  2017 screenshots/
drwxrwsr-x  2 mythtv mythtv 4096 Jul  5  2017 streaming/
drwxrwsr-x  2 mythtv mythtv 4096 Jul  5  2017 trailers/
drwxrwsr-x  2 mythtv mythtv 4096 Jul  5  2017 videos/
But you have to use mythtv-setup Storage Group editor to make the appropriate links see


Re: DVBSigMon errors

Posted: Fri Feb 23, 2018 10:32 am
by jl6tv
Hi Mike,

Thanks once again for your suggestions and apologies it's taken me ages to get back to you with the results.

First, the good news - something amongst your suggestions has caused this to work now! I did each of your steps in turn, and initially they made no difference. But then after some combination of repeating them, rebooting, rescanning for channels, stopping and starting the backend, it started working. I can't remember the exact order of what I did unfortunately.

I can now watch SD channels. HD channels though will play for 1-2 seconds, then grind to a halt with visual corruption, stuttering, and eventually will freeze the image on screen.

Mythfrontend gives me this output in the terminal:

Backend log:

Frontend log:
Do you have any suggestions?


Re: DVBSigMon errors

Posted: Fri Feb 23, 2018 12:57 pm
by MikeB2013
From the description it seems that the mythtv frontend settings may need adjustment, as you are running Intel CPU with Integrated Graphics (from your previous pastebin dmesg output):

1. Setup>Appearance set Paint engine to Auto (it is probably set to Qt).
2. Setup>Seup Wizard> set Video Playback Profile to VAAPI Normal, and run Test Standard Definition and Test High Definition, both test videos should playback with no problems.


Re: DVBSigMon errors

Posted: Tue Feb 27, 2018 6:57 am
by Pravesh
Hi i seek assistance from you guys. I just purchased a DVB T2 however when plugged the power it just says "boot" on the device display and just displays the dvb t2 start up screen and nothing happens from there. I kept it switched for more than 5 hours tries every possible connection possible however it just is stuck at boot. The remote doesn't have any impact on the device. Can any one tell me what could be the issue and if it need some work to be done on it.

Re: DVBSigMon errors

Posted: Sat Mar 03, 2018 6:08 pm
by jl6tv

Halfway through trying your suggestion I managed to pull the USB tuner out (silly me). I plugged it back in, and I was back to square one - nothing worked. I tried all kinds of combinations of deleting channels, rescanning, and rebooting, and finally got back to the point where everything worked.

I can now receive some channels perfectly (e.g. BBC One HD, Cbeebies HD), while others still suffer from the corruption/stuttering/"digital noise". The changes you suggested don't seem to make any difference (I've tried with your suggestions, and with what I had before).

Visually, it looks like exactly what I'd expect a poor signal to look like. But I'm doubting that, given that some channels seem to work much better than others which I understand to be on the same multiplex. I've also had no problems with all the HD channels when using the PCTV software in Windows.

Re: DVBSigMon errors

Posted: Sat Mar 03, 2018 7:44 pm
by Steve Goodey
Could it be that the signal you're getting is too strong? You might need to use an attenuator maybe?

Re: DVBSigMon errors

Posted: Sun Mar 04, 2018 11:06 am
by MikeB2013
You can measure the signal strength (and other statistics) on a tuner by using one of the dvb-tools utilities dvb-fe-tool.

For Ubuntu based systems install as follows:
sudo apt update
sudo apt install dvb-tools

Run like so in a terminal , having set LiveTV in mythfrontend to the desired channel (does not matter if picture poor)

dvb-fe-tool -m -v

to stop monitoring just press ctrl+c keys.

Paste the output from dvb-fe-tool -m -v for several channels both SD and HD

Here is an example output from one tuner on a quadHD Hauppauge DVB-T/T2 tuner

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mike@ssd-AB350-Gaming-3:~$ dvb-fe-tool -m  -v
Device Silicon Labs Si2168 (/dev/dvb/adapter0/frontend0) capabilities:
DVB API Version 5.11, Current v5 delivery system: DVBT2
Supported delivery systems: 
Got parameters for DVBT2:
FREQUENCY = 722000000
BANDWIDTH_HZ = 8000000
STREAM_ID = 4294967295
Lock   (0x1f) Signal= -39.00dBm C/N= 31.75dB UCB= 0 postBER= 0
Lock   (0x1f) Signal= -39.00dBm C/N= 32.00dB UCB= 0 postBER= 0
Lock   (0x1f) Signal= -39.00dBm C/N= 32.00dB UCB= 0 postBER= 0
Lock   (0x1f) Signal= -39.00dBm C/N= 31.75dB UCB= 0 postBER= 0
dvb-fe-tool defaults to the first tuner in /dev/dvb/adapter0, if you have more than one tuner you need to specify the adapter and possibly frontend with the -a and -f switches.

Note there is an older utility femon (sudo install dvb-apps), which is obsolete, but still available. You can try this as well if you like but I suspect with 292e it may not work:
femon -H