Some transformers in the power supplies provide a little humming noise and that is normal. If the humming in Von Duprin PS873 power supply is loud follow these steps. Remove the load from the outp...
Battery backup can be added to the PS900 series power supplies. Order the 900-BBK to get the battery backup board and batteries for field installation.
See Board Differences Battery Backup Circuitry for a picture of the visual differences between a F-Series biometric handreader with a main board that has the battery backup ci...