What to check

The DC voltage between terminals 1 and 2 on the reader should be about 12v. 

Corrective Action

Check PinNet controller power voltage and reader L1-L6 connections

If the reader is a significant distance from the controller there may well be voltage drop and this can be solved by doubling up using spare conductors.

L1    +12v DC
L2    -12v DC
L3    TX data L2 --- L3 0.5v AC
L4    TX data L2 --- L4 8.7v AC
L5    RX data L2 --- L5 2.0v AC
L6    RX data L2 --- L6 5.8v AC

Links

https://www.entryphone.co.uk/pdf/PinNetManualV5.pdf