Troubleshooting CM-7777 CM-7778 CM-7778HD Preamp Connections and Voltages

Preamp Connections and Voltages CM-7777 CM-7778 CM-7778HD

The following is the sequence to connect the CM7777, CM7778 or CM7778HD into your system.

Your Antenna>Short coax cable to the CM777X “Input” Port>”Output/Power” Port from CM777X connects to the long coax cable going into the house/structure>That long coax cable enters the house/structure and connects to the Power Inserter "To AMP" port>Power inserter "TO TV" port, is connected to a coax cable that goes to a TV or to a splitter. See the attached diagrams for reference. 

The 3rd coax port on the CM-7777, CM-7778 and CM-7778HD ‘Power Inserter’ labeled "DC IN", is connected to a coax cable that is in turn connected to the power supply adaptor that plugs into the wall power.

Voltage readings are taken while the CM7777, CM7778 or CM7778HD are not connected to the long coax cable that goes down into the house. (The short coax cable from the antenna can remain connected to the Preamp Input.) CM-7777 CM-7778 and CM-7778HD use the same ‘12VDC Output’ power supply; You should read about 13.2VDC at the end of any cable that connects to the output of the power inserter, "TO AMP" port. The 12VDC Power Supply has a green power light on it.

CM-7777 CM-7778; ‘15VDC Output’ power supply; You should read about 21VDC at the end of any cable that connects to the output of the power inserter, "TO AMP" port. The 15VDC Power Supply does not have a green power light on it.

Note; *Earlier CM-7777 and CM-7778 were shipped with 15VDC power supplies. Currently they are shipped with 12VDC power supplies. Both are equally correct.

Additional power supply troubleshooting; The 12VDC supply for the CM-7777, CM-7778, and CM-7778HD, has a constant green power light when connected to the wall outlet and operating normally. The green light will flash if the preamp is drawing too much current, or if the cabling between the power inserter "TO AMP" port and the Preamp "Output/Power" port has a short.

If you experience a flashing green light;

1. Disconnect the cable from the preamps "Output/Power" port. If the green light on the power supply returns to solid green, then the preamp has a problem.

2. If after step 1 the green light continues to flash, then the cable, or any other component that is connected between the Power inserter and the Preamp, must have a short from the center conductor to the shield/ground.

Note; If your antenna has a built-in preamp that requires power over the coax cable, installing the CM-7777, CM-7778 or CM-7778HD preamp and its power inserter will block the voltage from getting to your antenna's built in preamp and you'd likely get little or no signal to your system. This scenario can cause damage.

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