What to check

This version has a transformer for Speech and ringing and a Switch Mode unit for all video functions.

The Large Red LED (12v AC ringing) and Large Green LED (12v DC speech) should both be ON.

The video small Red LED (12v SW for camera) and small Green LED (20v SW for monitors) outputs are timed. The timer starts automatically when any phone is rung.

To start the timer momentarily link "SIG" to "-" the small Red & Green LED's should both come ON.

Check the fuses that are directly above the small LED's, both are 2 Amp 1.25" (32mm).

To check the Switch Mode PSU output, measure for 20v DC on the Red & Black wires.

Corrective Action

If you do not have 20v DC on the Red and Black wires, replace the Switch Mode unit.

If you do have 20v DC on the wires and the timer does not start, replace the 900C-PSU pcb.

There is a engineer's jumper between the terminal blocks, "timer lock" ON or OFF, you can move temporally to ON to start the timer.

Additional Notes

The S-100F-24 version of Switch Mode has a fuse inside.

These units can fail on mains surges or nearby lightning strikes.

Links

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