If your hps5, 10, 40 does not react to an entrance signal, but all functions work normally, try the following:
In first: open cover, cover of enclosure has 4 screws (fourth -in battery holder left angle, under yellow label QC/OK)
in second: examine BNC input connector, your hps can has infringement of connection from the central contact BNC- (input connector) to printed board.
At more connections PROBE, BNC connector has turns right-left, the tightening of a nut BNC weakens, BNC turn and wire from central contact BNC has broken.
You should fix nut BNC with by a Grower or glue, next solder wire.
But keep in mind that when you open the unit, you void the warranty.
If there is a problem during the warranty period, return the unit to your distributor.