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 TM 55-1905-219-14-9
4-47. ALARM SWITCHBOARD-MAINTENANCE INSTRUCTIONS (Continued).
(3) Trouble Alarm Operation.
(a) It the trouble buzzer, Z, operates, examination of the unit panels will show one or more yellow
targets showing. This is an indication that the circuit on which the target is displayed is open and out of order.
(b) The circuit in trouble should be disconnected by throwing the switch to "Off" for the same reason
that it would be disconnected for an alarm condition. When the circuit has been repaired, it can be switched
back into operation by simply returning the associated line switch to the normal position.
(4) Operation in Case of Grounds. Positive and negative ground detector lights are provided on the
alarm panel at the top section on of the alarm switchboard. Under normal conditions both ground lamps are
darkened. If either the positive or negative ground detector lamp glows, this is an indication of a ground in the
+ or - side of the power supply. For removal of these grounds, see paragraph e "Grounds". ANY
REPLACEMENT LAMPS MUST BE AGED. To age lamps, operate, 24 hours at 180 volts A.C.
c.
Description of Operating Circuits
(1) The electrical operation of the supervisory alarm system may be understood by a study of the wiring
diagrams (Foldout 1). These diagrams show the complete wiring of the alarm switchboard and the wiring for a
two line alarm unit. Other line alarm units are wired in exactly the same manner. The number of contact
makers may be varied as required.
(2) Supervisory circuit.
(a) Referring to the wiring diagrams (Foldout 6) the supervisory circuit may be traced from the positive
(red) terminal of the full wave selenium rectifier, through the winding of the alarm target relay, through the line
unit test switch to the " L"side of the line circuit. The circuit enters one side of the contact maker, through the
F
supervisory resistor to the other side of the contact maker to the "FFL" side of the line. The circuit continues
through the line unit test switch, through the supervisory target relay coil to the negative terminal of the rectifier
(b) With the current flowing in this circuit as outlined, the supervisory relay is energized sufficiently to
operate its armature, the alarm relay is also energized but not sufficiently to operate its armature, and the
supervisory resistor is in the circuit holding the current down to a point where the alarm target relay will not
operates. This current is approximately .012 amperes.
4-1201
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