An apparatus for indicating detection of an onset of a high-voltage condition at an output locus of a signal converter device, the signal converter device including a switching network for switchingly controlling a potential at a circuit node coupled with the output locus in response to a control signal received from a control signal source, includes: (a) a first sensing unit coupled for sensing a parameter at the circuit node; (b) a second sensing unit coupled for sensing the control signal; and (c) a comparing device coupled with the first sensing unit and with the second sensing unit; the comparing device effecting comparison of a first signal from the first sensing unit with a second signal from the second sensing unit. The comparing device effects the detection when the first and second signals have a predetermined relationship, then the apparatus effects the indicating.