No signal when temps get cold - Canadian TV, Computing and Home Theatre Forums

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post #1 of 24 (permalink) Old 2016-01-06, 11:06 PM Thread Starter
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No signal when temps get cold

Need some help troubleshooting a recent problem.
As the weather got cold here, i lost signal on all stations. It seems to happen only when the temps fall below freezing at night, then during the day it works again. I have an older model CM4221, CM 94444 balun, 6ft outdoor rated coax connected to mast mounted CM 7777 then 30ft outdoor rated coax from there to the inside. My thought is water got in something and is freezing causing a short because if I pull the coax out of the TV inside leaving only the center pin in contact I get signal but it is severely reduced. As soon as the outside of the coax makes contact signal is lost. I didn't seal any of the outside connections assuming that outdoor rated coax would be ok. Any suggestions?
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post #2 of 24 (permalink) Old 2016-01-06, 11:19 PM
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Cold also causes metals to contract, therefore you may have a poor connection somewhere - check them all. Also, check for proper grounding.

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post #3 of 24 (permalink) Old 2016-01-07, 04:44 AM
 
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sempei, I think you are correct about it being some kind of short, but not water. Even though it is outdoor rated coax, it may not be rated for cold temperatures. I had a similar problem where the outer plastic casing shrunk so bad the center conductor was about 3/4" long and was bent had started to pull the connectors off. Whether it was just a bad batch of coax where some stabilizer was left out or something who knows, I replaced the coax which resolved the issue. A little time and new coax, a relatively cheap repair.
Alternatively if the center conductors are long you could just trim them down, but they maybe too short once summer and heat comes into play.

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post #4 of 24 (permalink) Old 2016-01-07, 11:18 AM
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The expansion issue is really that plastic expands and contracts more than metal with heat and cold. It's a common problem with outdoor installations with very long cable or conduit runs. In this case the outer sheath could expand and contract more than the center conductor, possibly causing a short or loss of contact at a weak termination. With a 6' coax run, I wouldn't expect this to be an issue but it is possible. Water and ice could cause the same effect.

I wouldn't rule out the possibility of a defective preamp or water ingress into a component such as a balun or a connector. The only real way to tell is by close inspection of all connections and components. At terminations, make sure the center conductor is not too long or too short and the outer sheath is securely attached.
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post #5 of 24 (permalink) Old 2016-01-07, 12:28 PM Thread Starter
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I already assumed that I was going to have to get back up on the roof and check the connections. The antenna has only been up for a few months and has been working flawlessly until the cold weather hit here in central PA. I will check all the connections, especially the length of the center conductor on the 30" length of coax.
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post #6 of 24 (permalink) Old 2016-01-07, 03:43 PM
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As a quick check, just go and do a poor man's setup and run long-ass RG6 or RG11 cable from the antenna to your TV. Then just start adding your pre-amps, etc. back into your setup one-by-one. If one piece of equipment kills everything, presumably that is what bad. If you add your pre-amp and your rotor, etc. all back and your signal kept, you know it was something with the existing coax in your system.

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post #7 of 24 (permalink) Old 2016-01-07, 07:09 PM
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we don't really need to see RF signal in order to just verify the
current draw. To measure the current draw of the preamp, break the
connections at the power inserter to the downlead coax.
Insert a DMM setup to measure DC current and insert it in series with the
center pins of Pwr inserter and downlead coax. Can use two alligator clip leads for this. Then bridge the two outer shields
together with one more alligator clip lead to complete the circuit.

If no current is drawn, there's an open circuit somewhere in the system.
If way too much current draw, there's likely a short somewhere in the system.
if it looks about right relative to MFR's specification then you probably have some other problem.

Alternatively, you can just go up to the preamp end and remove the Downlead connection, put a DMM across
the center pin and shield. If no DC Voltage is seen at that point, it will never draw any current when it's connected
to a load (the preamp).

there used to be a video on the Channel Master Support site, but I couldn't find it
when looking just now. A shame, because they can explain/demonstrate better than I can.

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post #8 of 24 (permalink) Old 2016-01-08, 08:32 PM
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sempei

Which 7777 do you have, the old model with separate inputs for VHF and UHF antennas, or just one all channel input?

Channel master has a troubleshooting page for the new 7777 and I can show you photos for troubleshooting the old 7777 with the 0747 power supply/inserter without needing to go up to the antenna similar to majortom's technique.

If you can not measure it, you can not improve it.
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post #9 of 24 (permalink) Old 2016-01-08, 10:23 PM
 
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Mr. Rabbit, sir.

I'd love to see what you have on troubleshooting the original dual-input 7777. Mine has just mysteriously crapped out on me.

It worked all through first the snow storm of the season, and the subsequent rain/ice shower. The next morning, bright sunny and clear, it also worked as expected - but when I got home later that day there was no signal. Not a degraded signal - it was 0 on every channel, not a flicker to be had. I've checked all connections, and even bypassed the preamp entirely. Reception is as would be expected without a preamp - fewer channels and weaker, but steady, signal strength.

I haven't yet swapped in a spare preamp to confirm it's the 7777 (have to go pry it out of a friend's hands), but the fact that there are 14 channels without using a preamp and no signal at all when the preamp/power inserter are put back into the loop leads me to that assumption. The 7777 was only 4 or 5 years old, and extremely well shielded from the weather.

Please post at your convenience, but anything you can provide would be most helpful.

Thanks...Steve
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post #10 of 24 (permalink) Old 2016-01-08, 10:45 PM
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Hi, Steve

I have to go to bed now, but take a look at these two posts and let me know if you have any more questions. I will check back tomorrow.
Signal Amplifiers (Amps, Preamps, Distro Amps)
Signal Amplifiers (Amps, Preamps, Distro Amps)

If you can not measure it, you can not improve it.
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post #11 of 24 (permalink) Old 2016-01-10, 06:07 PM
 
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Rabbit73

Thanks much for pointing me to those posts. Great information, very helpful.

However, things have muddied up. Swapped in an AD PA-16 (?) yesterday and it worked. So I reconnected the original 7777 and IT worked. But...got up this morning and it was all gone again. Swapped back in the AD preamp and now it doesn't work either.

It's been raining, but that doesn't sound like water. Maybe a short in a cable? I DID add a 6 foot cable to get from a long RG-11 run to the preamp about a month ago. Perhaps I did a poor job adding the connectors, or the cable had a break in it.

I'll break out the ohmmeter and replace/eliminate the latest cable addition for more testing.

Thanks again for the help. SS
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post #12 of 24 (permalink) Old 2016-01-11, 12:31 PM Thread Starter
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Rabbit73,
It is the newer model 7777 with single input. I'm not convinced that the 7777 is the problem anyway, as the temps warmed up this weekend everything worked perfectly again.
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post #13 of 24 (permalink) Old 2016-01-11, 01:17 PM
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Quote:
It is the newer model 7777 with single input.
Here is the troubleshooting page for the new 7777:
How do I troubleshoot my CM7777 preamplifier to make sure it is working correctly? ? Support

I haven't done tests on the new 7777, so I don't know what the normal voltage readings should be when the preamp isn't connected and when it is. As majortom described in post 7, you will need access to the center conductor to measure the voltage under load, and you will need to insert a current meter in series with the center conductor to measure the current drawn by the preamp.

If you can not measure it, you can not improve it.
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post #14 of 24 (permalink) Old 2016-01-11, 04:00 PM
 
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Quote:
I haven't done tests on the new 7777, so I don't know what the normal voltage readings should be when the preamp isn't connected and when it is.
I have. It's 15 volts and the (new) 7777 usually draws about 250 mA, a real power hog. It has a two stage amp in it, each draws around 125 mA off an internal 8 volt regulator. The supplied power block is rated at 300 mA. The old 0747 supply will not run the new 7777, but the new supply is backwards compatible.

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post #15 of 24 (permalink) Old 2016-01-11, 04:54 PM
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Thanks for the info on the new 7777.

Does the power supply for the new 7777 have protection against coax shorts like the 0747 power supply had; a solid state resettable fuse?

If you can not measure it, you can not improve it.
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