Broadcast Electronics AM-2.5E, User Manual

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1-91.
FAULT CIRCUIT.
Exciter, power supply, RF power module, reflected power high, reflected
power emergency, over-temperature, lightning, or a 1.2 : 1 VSWR conditions are
monitored for faults by individual status circuits. In the event of a fault, the appropriate
circuit will latch the fault for display by the controller circuit board indicators. If a circuit
detects a fault condition, a HIGH signal will be applied to NOR gate U55. U55 will output
a LOW to inverter U54F. U54F will output a HIGH to bias alarm driver transistors Q34
and Q35 on to illuminate the alarm indicator.
1-92. When a fault condition is removed, the fault circuit latch must be manually reset using
the reset switch. When the reset switch is depressed, a HIGH reset command is applied
to OR gate U12C. U12C will output a HIGH reset command to latches U48A, U48B,
U48C, U48D, U49A, U49B, and U49C. The Q output of each latch will go LOW. The
LOWs are applied to NOR gate U55. U55 will output a HIGH to inverter U54F. U54F
will output a LOW to bias driver transistors Q34 and Q35 off to extinguish the alarm
indicator.
1-93.
OSCILLATOR CIRCUIT.
Reference frequencies for controller circuit operation are
provided by an oscillator circuit. The oscillator circuit consists of: 1) comparators U40C
and U44B, 2) resistors R24, R28, R27, R29, R30 and R31, 3) capacitor C38, and 4) inverter
U46A. The oscillator is designed to output a 1 kHz square wave signal. Oscillator
symmetry control is provided by resistors R24 and R27. The oscillator frequency is
controlled by resistor R29 and capacitor C38.
1-94. Integrated circuit U40C compares a 1 kHz signal to a reference voltage. As a result,
U40C will output a ramp signal to comparator U44A. U44A uses the signal to generate
the power control PWM signal. The ramp symmetry is controlled by R30 and R31.
1-95.
OVER-CYCLE OFF CIRCUIT.
The controller circuit board is equipped with an over-cycle
circuit. The circuit is designed to prevent damage to the crowbar resistors on the power
supply circuit board during 7 transmitter on/off cycles within 15 seconds. Conditions
causing the transmitter to over-cycle off include ac failure and manual on/off control
operation. The circuit consists of AND gate U22A, inverter U25F, pulse generator U59B,
capacitor C132, and comparator U44D.
1-96. The circuit monitors the transmitter off, power supply mute, and ac fail conditions. AND
gate U22B provides off signals during manual off operations. NOR gate U23A provides
an off signal during power supply mute conditions. AC fail provides an off signal during
ac fail conditions. During a transmitter off operation, a LOW from AND gate U22B, NOR
gate U23A, or AC fail is applied to AND gate U22A. U22A will output a LOW to inverter
U25F. U25F will output a HIGH: 1) to pulse generator U59B and 2) power inhibit signal.
U59B will output a HIGH to capacitor C132. If the transmitter is operated to off 7 times
within 15 seconds, capacitor C132 will charge and provide a HIGH to comparator U44D.
When the voltage increases above the reference, U44D will output a HIGH over-cycle off
command to OR gate U37B. U37B will output a HIGH emergency off command to operate
the transmitter to off if one of the following conditions occur: 1) open cabinet or external
interlock, 2) power supply emergency, 3) over-cycle off, or 4) the ac line is above 260 Volts.
The emergency off signal is routed to the remote panel by transistor Q56.
1-97.
POWER SUPPLY CIRCUIT.
The controller circuit board operates from ± 15 volt dc
supplies. The +15 volt supply is equipped with a battery backup system. A nine volt
battery provides a dc supply to maintain the controller logic during an ac power failure.
Switch S5 allows the battery to be tested. When switch S5 is depressed, the battery
voltage is applied to comparator U44C. If the battery voltage is above the reference, the
output of U44C will go LOW to illuminate battery ok indicator DS1.