What to check

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

900-VS4 video distributors have 4 outputs, if all outputs have failed, check the 20v + - input voltage and the incoming Coax.

Corrective Action

Beware of tucking excess unsheathed coax behind the 900-VS4 pcb as this cause shorts.

Replace 900-VS4

Links

https://www.entryphone.co.uk/shop/productdetail/900-VS4