Sporadic loss of all channels

M

mxplut

New Member
Let me first say that I am happy to concede that my problem may not be anything to do with my hummy. Still, it all started when i installed it.

Since getting my box a week or two ago I have lost signal on all channels several times. Absolute zero, as if the antenna came out. My wife has experienced it too. Most distressing with a household demographic that overwhelmingly requires cbeebies in the afternoon. The most troubling aspect is that not only does the hummy suffer total loss of signal, so too does the TV. A retune finds no channels.

This evening when we switched on there was no signal so I checked a number of things.
1. The tv attached to outlet 2 on my amp was fine. Normal signal
2. With aerial routed through the hummy i was getting zero signal on the hummy AND zero signal on the TVs built in tuner
3. With the aerial routed directly to the TV i still got zero signal.
I checked connections, I checked the coax cable for shorts and breaks. All ok
4. I attached my spare TV to the aerial lead that had been attached to the hummy and I got a signal.
5. I reconnected the aerial to the hummy and the signal was back again for both the hummy and the tv

So, I seem to have an intermittent event where the hummy and the TV connected to it lose all signal only for it to return several minutes to an hour later. I am at a loss to explain it and am being stung by the comment from my dearest that we never had a problem before I bought that box!

Please help me get to the bottom of this!
Thanks
 
There are various possibilities, but one which strikes me is interference from the HDMI lead to the aerial lead. Whenever you got zero signal, was there a live HDMI between the Humax and the TV (even if it was not being displayed)?
 
Yes. There is a live hdmi connection between the two. Could that do it, even when the aerial is routed directly to the tv?
 
You obviously had to disturb your co-ax cabling when you connected your new Humax box, the most likely cause is a bad co-ax connection. You should expect to measure a short circuit between inner and outer parts of the co-ax plug from your aerial, because although it is 75 Ohms at UHF frequencies it will be a short circuit to DC.
 
mxplut said:
Yes. There is a live hdmi connection between the two. Could that do it, even when the aerial is routed directly to the tv?
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It could. The frequencies in an HDMI signal are similar to UHF TV. Try separating them out, or just unplug it. As final proof you could connect the Humax to the TV by SCART (temporarily).

If that proves to be the problem, a better quality coax will probably solve it. Those thin (4 or 5 mm) cables frequently supplied for interconnecting are crap. I advise the proper downlead coax (I think it's about 8mm), and enthusiasts use satellite cable even for UHF TV.
 
Ok, learning fast. With the aerial connected to the coax i should measure a DC short? Makes sense. aerial is just a wire loop. I did not try that. I tested the cables disconnected. Will try that next time i get the issue.
 
Now you have two possible lines of attack. Under normal circumstances I would favour a connection problem, but you seemed to have eliminated that.
 
Just for balance, it could be worth watching your TV using it's internal tuner and then removing the HDMI cable from your Humax to the TV, It is quite rare but the signals in the HDMI cable have been known to cause interference, It is quite an uncommon problem though
 
mxplut said:
Ok, learning fast. With the aerial connected to the coax i should measure a DC short? Makes sense. aerial is just a wire loop. I did not try that. I tested the cables disconnected. Will try that next time i get the issue.
Click to expand...
Be careful - this does not necessarily follow. Whether you see a short at the end of the co-ax connected to the antenna depends on the antenna itself. Some will show a short circuit and others will not. Also, from your first post it appear that you have an amplified splitter between the antenna and your receivers, so you will almost certainly not see a short circuit when measured from the TV side of the amplifier. In this case, if you measure a short then it would point to a problem with your cabling.

My best guess from the symptoms is a dodgy cable. If its a shop bought one then it could easily be the culprit. I always make up my own cables when I can to make sure they are made well. There is a guide to how to terminate co-ax cables on the Satcure website. I would post a link, but the system won't let me as I don't have enough posts to my name yet!

Good luck!
 
Thanks for the hints. Had the same problem this evening and further observation suggested that some of the things that I had said in my earlier post were not correct. Notably, my spare tv had also lost signal. The signs are pointing towards a duff cable somewhere between the antenna and the amplifier-splitter. Or it could be the amplifier itself that is goosed. Actually, the antenna feeds into a powered interference filter and that feeds the powered amplifier-splitter. I didn't install that stuff myself. My house is full of surprises left by the previous occupants.

Next time I have the chance i'll try bypassing all the electric guff in the loft and see if I get anything.

I really appreciate all your advice. Thanks a lot. It certainly seems that none of this is the Hummy's fault, so that is one less thing to worry about.
 
Now we have been through analogue switch-off, it is also possible the signal is too strong. Certainly if you have any amplifiers, try it without.
 
Unfortunately the signal is very poor without the filter. The amp is probably surplice to requirements now. But I discovered something frankly frightening when I was connecting and reconnecting.

Is there any reason at all why the patch cable between the loft and the lounge has got 60v AC running on both the inner and the outer. I got a belt off something while bypassing the amp and that's what I got measuring to earth.

Down in the lounge i measure 5v on the outer to earth. Nothing on the inner. Perhaps the previous occupant of the house has put another amp somewhere concealed that is slowly cooking my tv and hummy. And about to burn my house down.

I think it may be time to call in the pros
 
That does not sound nice, and should not appear at the receiver end in any case. If you have a mast-head amplifier it is common to send them power up the signal lead (this is called "phantom power") from a supply device (which then passes signal only downwards). The supply would be 5 or 12V DC though, not AC.

The Humax itself is capable of providing 5V power up the incoming aerial lead, if turned on in the settings (Menu >> Settings >> Installation >> Antenna Power).
 
It is possible to measure an AC voltages on any un-earthed cable that runs parallel to mains wiring for any length, BUT it will be at extremely low currents. If you actually get a shock from it I don't think the AC voltage you are measuring is being induced into the cable by running parallel to mains wiring, so it must be coming from the powered filter or in-line amplifier and It shouldn't be there
 
Anything with a filtered mains input needs an intact earth connection, otherwise the chassis floats to typically half mains voltage. Been there, done that, bought the tee shirt.
 
mxplut said:
Actually, the antenna feeds into a powered interference filter and that feeds the powered amplifier-splitter. I didn't install that stuff myself. My house is full of surprises left by the previous occupants.
Click to expand...

Can you elaborate on what this powered interference filter is, and what it does? I know about in-line amplifiers, and also filters, but have not come across powered filters for domestic TV use. Do you mean "Antiference" by any chance? A make and model number might help us understand better the arrangement you have there. As Black Hole says, since DSO many people are now suffering with too much signal level which can cause problems, including overload and picking up multiple transmitters.
 
Hi moose. You're right. Silly me. It is an Antiference amplifier that is mains fed. It takes the line from the aerial on the roof and feeds directly into a second amplifier/splitter.

Since last time I wrote I've not had any problems. I tried to look for the 60V load that was giving me shocks and I can't find that either. Most frustrating. By the way, anyone know if a neon screwdriver will light up at 60v 50Hz, or does it need the whole 220V

Maybe the ghosts in wiring have had their fun and have now departed. If I lose signal again and if the 60v comes back then I'll be straight back on here.

Thanks for all your advice.
 
mxplut said:
I tried to look for the 60V load that was giving me shocks and I can't find that either. Most frustrating. By the way, anyone know if a neon screwdriver will light up at 60v 50Hz, or does it need the whole 220V
Click to expand...

The minimum voltage to start a neon is usually about 90Volts
 
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