TV Fool  

Go Back   TV Fool > Over The Air Services > Special Topics > Antennas

Notices

Reply
 
Thread Tools
Old 26-Aug-2020, 10:31 PM   #1
alphonsobellinni
Junior Member
 
Join Date: Mar 2018
Posts: 3
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 is offline   Reply With Quote
Old 27-Aug-2020, 2:52 PM   #2
alphonsobellinni
Junior Member
 
Join Date: Mar 2018
Posts: 3
To clarify. The clamped/grounded connector is on the antenna side of the preamp.
alphonsobellinni is offline   Reply With Quote
Old 27-Aug-2020, 5:45 PM   #3
rabbit73
Retired A/V Tech
 
Join Date: Aug 2012
Location: S.E. VA
Posts: 2,683
Quote:
Originally Posted by alphonsobellinni View Post
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:





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
Attached Images
File Type: jpg RCAPreampVload3.jpg (272.7 KB, 346 views)
__________________
If you can not measure it, you can not improve it.
Lord Kelvin, 1883
http://www.megalithia.com/elect/aeri...ttpoorman.html

Last edited by rabbit73; 27-Aug-2020 at 6:03 PM.
rabbit73 is offline   Reply With Quote
Old 28-Aug-2020, 2:53 PM   #4
alphonsobellinni
Junior Member
 
Join Date: Mar 2018
Posts: 3
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.
alphonsobellinni is offline   Reply With Quote
Reply

Bookmarks

Go Back   TV Fool > Over The Air Services > Special Topics > Antennas


Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off




All times are GMT. The time now is 1:58 AM.


Powered by vBulletin® Version 3.8.8
Copyright ©2000 - 2021, vBulletin Solutions, Inc.
Copyright © TV Fool, LLC