What to check

The first video distributor is in the power supply and has 2 ports,

First check that you have incoming video from the door camera, about 6v DC between D1 & D2 to D4. Then check you have similar voltage on the outputs 1 & 2 to 4.

A symptom of the Video picture starting to Roll is a failing component

Corrective Action

Replace 500R PCB or if only one output is used, adapt connections to bypass video components.

Additional notes

Two types:

PCB-DA500-R with long Pins

PCB-500PSU-R with Red & Black leads.

Links

https://www.entryphone.co.uk/shop/productdetail/PCB-DA500-R

https://www.entryphone.co.uk/shop/productdetail/PCB-500PSU-R