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Old 27-Aug-2020, 4:45 PM   #3
Retired A/V Tech
Join Date: Aug 2012
Location: S.E. VA
Posts: 2,708
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

CM-7777, CM-7778 Titan 2 & CM-7778HD detailed troubleshooting. (CM7777 CM7778)

Amplifier Support
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If you can not measure it, you can not improve it.
Lord Kelvin, 1883

Last edited by rabbit73; 27-Aug-2020 at 5:03 PM.
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