To check the RCA, you have to make some voltage measurements.
First you check the voltage coming out of the power inserter without the preamp connected:
Next, you check the voltage at the upper end of the coax without the preamp connected:
Then you check the voltage to the preamp with the preamp connected. This is a little more difficult, because you need access to the coax center conductor when the preamp is connected. I use a T-adapter:
