What to check

The power supply once started only provides 20v for typically 1 minute before timing out.

Start the PSU timer by shorting "SIG" to "-" wires, (you will need to check at phone or PSU for the wires colours).

Check the 20v + - input voltage and then the >video distributors incoming Coax will only have about 1v while the power supply is running.

Corrective Action

Check other end of feed Coax, reconnect.

Beware of tucking excess unsheathed coax behind the pcb as this cause shorts.