No signal when temps get cold - Page 2 - Canadian TV, Computing and Home Theatre Forums

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post #16 of 24 (permalink) Old 2016-01-11, 08:36 PM Thread Starter
Join Date: Oct 2015
Location: Selinsgrove, PA USA
Posts: 11
I did manage to climb on the roof this afternoon and check all the cable, but not were showing any center conductors with extra length. They were all about 1/8" - 1/4" past the edge of the connector. The one balun to antenna connection was loose which I tightened but need to wait until this evening when it gets cold again to evaluate. If this doesn't solve the issue, the only thing left would be the antenna itself, the balun or the CM7777. Just seems odd that it works perfectly when temps are above freezing.
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post #17 of 24 (permalink) Old 2016-01-11, 08:50 PM
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Did you measure the DC voltage coming from the Power Inserter with a digital Voltmeter or the current draw of the preamp while you were up there?

DB4E/VHF Yagi rotor FM Bandstop ap-8700 preamp 4way split LG lcd.
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post #18 of 24 (permalink) Old 2016-01-11, 10:51 PM Thread Starter
Join Date: Oct 2015
Location: Selinsgrove, PA USA
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The loose balun connection wasn't the culprit, no signal again tonight when it got cold. I didn't check any voltages when I was up in the afternoon because everything was working perfectly. I can't really check anything on the roof when it's not working unless I climb up in the dark and that doesn't sound like a good idea. I''l run thru the checklist from the Channel Master site that was posted and see what readings I can get from inside I guess.
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post #19 of 24 (permalink) Old 2016-01-11, 11:24 PM
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You can measure the current draw from the ground, as I described earlier while it's broke, make a note of it. Then measure it again when it warms up outside again and it's working, again from the ground. Since you measure current by placing the ammeter in series with the load, it doesn't matter which end of the downlead you insert it. The reading will be the same.

DB4E/VHF Yagi rotor FM Bandstop ap-8700 preamp 4way split LG lcd.
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post #20 of 24 (permalink) Old 2016-01-12, 11:36 AM
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Does the power supply for the new 7777 have protection against coax shorts like the 0747 power supply had; a solid state resettable fuse?
Yes, it appears to have a PTC in its output circuit. I have observed that you have to actually unplug the wall wart from the receptacle or disconnect the load in order for the thermistor to cool off and reset, restoring the output. Simply removing the offending short isn't enough as the usual current flow then seems to keep the thermistor warm enough so only a part of the needed current can flow to the load.

No-load voltage of the power supply is around 18-22 volts; with the 7777 connected, it drops to around 14-15 volts. It's not regulated at the wall wart, the regulator is in the amp module (7808-type).

Something just crossed my mind (always a danger signal ). Perhaps it's not a problem with the antenna system itself, but rather a household device that comes on when the temp drops below a specific threshold and is emitting RFI. Easy enough to check, just start throwing breakers when the signal is out and see if it comes back when any specific circuit is de-energized.

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post #21 of 24 (permalink) Old 2016-01-15, 12:14 AM Thread Starter
Join Date: Oct 2015
Location: Selinsgrove, PA USA
Posts: 11
The problem is definitely with the CM7777. Put up my previous Winegard LNA-200 Boost XT tonight and as the temps fell it performed perfectly. The signal strength is not as strong on most stations as when the CM7777 actually worked, but I have signal when it gets cold at least.
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post #22 of 24 (permalink) Old 2017-01-17, 07:18 AM
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7777 amp has 75% plus failure rate in cold temps

I am self employed, ModernTech Solutions Alpena, MI. I install tv antennas, all sat. TV and internet, pre-wire new homes for data, tv etc., professional cell boosters, erect towers etc. I also do head end work and climb the big towers. Channel master has an issue with the 7777 amps. My distributor stopped carrying them six almost a year ago. Before he did that he would put the amps in the freezer for the night and test them one at a time the next day, 75% failure rate. I have had six amps go down when the weather up here got cold. A couple I have moved the amp to the inside of the house for now. Channel master tech support is a joke and won't admit to the problem, they know it is a problem as they finally admitted to my distributor. They claimed they fixed the problem with the new improved 7777 HD amp, that proved to be the same right away. They pulled it over six months ago, if you try to buy one on their sire it says out of stock. The reason is because they fail in the cold. I also compared two failed ones side by side after warming them to room temp., there was a 5 db difference in gain. They also are snubbing me on returns because these were installed in the summer and the warranty is out. I stopped using them because I had to. This was and is the only 30 db gain amp on the market, I need that in my area so that part of my business will most likely get cut in half. Channel master is the worst company I have ever dealt with and they are lying about the issue they can't seem to pin point. The old amps with two inputs were fine, then PCT merged/bought them and shipped all ops to china, thats when it started. So, if you have the newer 7777 in the equation, there is no way to trouble shoot with that variable. Try this amp, next best thing

ModernTech Solutions
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post #23 of 24 (permalink) Old 2017-01-17, 02:21 PM
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Thanks for the report on the 7777. The 7777 I just received came with a different power supply (12V instead of 15VDC output) and a different power inserter. The gain measured about 22 dB instead of 30 dB. I think they have been messing with the design to reduce the overload problem, but they should have retained the original design with 2 antenna inputs.

If you can not measure it, you can not improve it.
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post #24 of 24 (permalink) Old 2017-01-27, 08:27 AM
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Interesting about the 7777. I had a 7778 I bought in about 2007 with the separate UHF/VHF at it work well for me for 7 or 8 winters than started failing in cold temps only on the VHF side. Swapped it out for a new 7778 (single input) a couple of years ago and my cold temps issue has been resolved.

A-D DB4e & CS5, CM 4221 & 7778, TiVo Premiere & Roamio
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