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 TM 55-1905-220-14-9
4-48. ALARM SWITCHBOARD - MAINTENANCE INSTRUCITONS (Continued).
(d) First, if the "Trouble Test" lamp, PL3, does not flash properly, the trouble may be due to the
supervisory target relay contacts not making good electrical contact. These contacts should be adjusted to
make good electrical contact when the supervisory relay armature is not operated. The supervisory target relay
is the top relay on the two line unit panel.
e) Second, if the supervisory relay contacts are not closing properly, the relay armature may be
binding due to dirt or foreign matter. Any such dirt or foreign matter should be removed and the armature
adjusted to close and open easily without bind.
(f) Third, if the relay contacts and armature are adjusted and operating properly, and the yellow
targets still fail to show when the circuit test switch is being thrown, the trouble may be due to residual
magnetism in the core of the relay coil. This must be corrected by replacing either the relay coil or the
complete relay.
(5)
Description of Silent Trouble Test Circuits.
(a) When the alarm panel test switch, S, is thrown from normal to the "Silent Trouble Test"
position, the swinger 9 (see wiring diagram (Foldout 1)), of the switch, transfers the circuit "T" from the buzzer,
Z, to the "Trouble Test" light, PL3; also, the swinger 5 applies negative voltage to energize the flashing circuit
of "Test Light", PL1.
(b) This operation of the switch opens the circuit to the trouble buzzer and prevents its operation
as long as the switch is maintained in this position. It also switches the "Trouble Test" lamp, PL3, into the
circuit in place of the buzzer, Z.
(c) The operation of the "make" spring completes the circuits to the "Test Light", PL1, and causes
it to operate the same as it does on the silent alarm test.
(d) With the silent alarm test switch, S, in the "Silent Trouble Test" position, the individual line
circuits are tested for trouble operation by moving the line circuit test switch SLOWLY from "Normal" to "Off"
position. As this switch is moved, the first part of its operation opens both sides to the line circuit, thus breaking
the supervisory current in that circuit. As the supervisory relay drops out, it completes a circuit to the "Trouble
Test" light, PL3, on the alarm panel.
(e) The circuit for the "Trouble Test" lamp, PL3, may be traced from the source of supply,
terminal "L1", through the "Trouble Test" lamp, PL3, to contacts 9 and 12 of the "Silent Trouble Test", switch, S,
through the contacts 1 and 4 of the two line unit test switch, through the contact of the supervisory target relay
to the
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