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-   -   Strange event with CM7777 system (http://forum.tvfool.com/showthread.php?t=16781)

alphonsobellinni 26-Aug-2020 9:31 PM

Strange event with CM7777 system
 
About one year old CM7777 amplfier set up suddenly went blank for a few seconds then came back. A few days later no signal detected for several hours. Next day normal operation. Yesterday cut out after a few minutes. Power inserter and power supply connections seem okay.Tinkering with connections on mast. Everything seems okay, connections are all tight, baluns all attached, etc. Accidentally bumped a cable connector against the mast and got full signal. Have connector clamped to mast with vise grips. Totally baffled by this..

alphonsobellinni 27-Aug-2020 1:52 PM

To clarify. The clamped/grounded connector is on the antenna side of the preamp.

rabbit73 27-Aug-2020 4:45 PM

1 Attachment(s)
Quote:

Originally Posted by alphonsobellinni (Post 63153)
To clarify. The clamped/grounded connector is on the antenna side of the preamp.

Hello, alphonsobellinni; welcome to the forum.

Is the mast grounded?

In order for the preamp to receive power from the power inserter, current must be able to flow on the center conductor and the shield of the coax that is between the preamp and the power inserter.

It sounds like when you allow the connector to touch the mast, current is allowed to flow to the preamp.

If it isn't that, it could be an intermittent connection in the coax. There are three possibilities:
1. An open in the center conductor
2. An open in the coax shield
3. A short between the center conductor and the shield, often caused by a strand of the shield making contact with the center conductor inside the coax connector

First you have to measure the voltage coming out of the power inserter.

Next, you have to measure the voltage at the preamp when it is connected to the upper end of the coax. This is difficult to do, because you need access to the center conductor of the coax when it is connected to the preamp.

I use a coax T-adapter:

http://forum.tvfool.com/attachment.p...8&d=1511635684

http://forum.tvfool.com/attachment.p...9&d=1598546702

Troubleshooting CM-7777 CM-7778 CM-7778HD Preamp Connections and Voltages
https://support.channelmaster.com/hc...-and-Voltages-

CM-7777, CM-7778 Titan 2 & CM-7778HD detailed troubleshooting. (CM7777 CM7778)
https://support.channelmaster.com/hc...CM7777-CM7778-

Amplifier Support
https://support.channelmaster.com/hc...lifier-Support

alphonsobellinni 28-Aug-2020 1:53 PM

Using a test procedure from Channelmaster support, I figured out the problem: dodgy coax from power supply to preamp. More than likely an open in the shield, as you mentioned.

Wiggled and jiggled cable and it is working normally at the moment. Replacing cable this weekend.

Thank you for the response and suggestions.


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