Quantcast Initial Fault Isolation Procedure

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MIL-HDBK-1023/4
(6) If the short circuit current is out of tolerance and is approximately the same as
the load current, then the fault is in the input voltage, control circuits, or regulator.
(7) If the short circuit current is normal but the load current is too high or the load
is affecting the regulator output; then too much reactance is in the circuit likely to be the
problem. Check for the following routine maintenance faults at any lights that are not operating,
and replace or repair them as required:
(a) Burned-out lamps.
(b) Opens in the secondary circuit of isolating transformers.
(c) Faulty isolating transformers.
(d) If the maximum brightness current if still too high when lamps are back in
operation, perform par. 6.4 checks first; then check for adapter units newly connected into the
circuit. If these adapter units cannot be moved to another circuit, reset the incoming voltage tap
so that the load current is correct. On regulators with output current adjustment controls,
carefully follow manufacturer's instructions and adjust output current to proper levels. Use
extreme care to assure that accurate true RMS ammeters are used to measure output current
levels.
(8) If the short-circuit current is normal, but the load current is too low, then the
regulator is probably overloaded due to a series fault or a new load added to the circuit, or the
voltage protective device is malfunctioning.
(9) If the short-circuit current is normal but the load current is zero, then there is an
open fault in the field circuit, or the regulator is greatly overloaded, or the runway selector
cabinet wiring is faulty.
d. If the load current is normal with the circuit energized, visually check the operation
of the lights in this circuit.
(1) If some, or all, of the lights are dim or out, de-energize the regulator and
proceed as follows:
(a) Beginning with the first unlighted or dim unit from each end of the faulty
section of the circuit, progressively check each faulty light along the circuit for each of the
following routine maintenance faults. If the faulty lights at each end of the faulty section are
found without these faults, the remainder of the units in this section need not be checked. Make
the required repairs as each fault is located.
1. Burned-out lamps.
2. Wrong type of lamps.
3. Blown or omitted film cutouts (where used).
4. Shorts or grounds in the isolating transformer or in the wiring of the
unit.
(b) If some of the lights are still dim or out, there are grounds or shorts in the
circuit between the lights of satisfactory intensity and the adjacent lights of unsatisfactory
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