Broadcast Electronics FX-50, Инструкция по эксплуатации

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©2011 Broadcast Electronics
Test point TP2 is employed to determine the condition of the LCD display. When +5 volts is applied to TP2, U7
will activate all segment control lines which illuminates all DS12 display segments.
Meter calibration control R56 is provided to adjust the multimeter for an accurate indication in the test meter
mode of operation.
PAV METER OPERATION. When the PA voltage function is selected, input switch U6B will operate and route a
sample voltage to the input of A/D converter/display driver U7.
PAI METER OPERATION. The PAI meter circuit utilizes two voltage-to-current converter circuits. The first consists
of integrated circuit U5B, current amplifier Q2, resistors R6, R7, and meter shunt R62/R63 (located on the
power/supply control circuit board).
When PA current flows, a voltage is developed across R62/R63 and routed to the input of U5B through R6. The
output of U5B is routed to amplifier Q2 which applies feedback to the inverting input of U5B to maintain circuit
stabilization. The amplified current through Q2 will develop a voltage across R7 in proportion to the collector
current for application to a second converter.
The second converter consists of integrated circuit U5A, current amplifier Q3, resistors R8, R47, and input
switch U6C. The operation of this circuit is similar to the previous circuit with the following exception. The
voltage developed across Q3 collector resistor R47 is routed to the A/D converter/display driver through input
switch U6C.
AFC METER OPERATION. When the AFC voltage meter function is selected, input switch U6D will operate and
route a sample voltage to the input of A/D converter/display driver U7.
TEST METER OPERATION. When the test meter function is selected, input switch U3C will operate and route
test probe potentials to the input of U7 through buffer U4B.
METER FUNCTION PRESET CIRCUIT. A meter function preset circuit consisting of resistor R61, capacitor C32,
transistor switch Q4, and one shot U8B automatically selects the forward power meter function when exciter
primary power is applied. Q4 will output a LOW to U8B as C32 charges through R61. U8B outputs a
momentary HIGH to forward power meter function switch S1 and the input of meter function encoder U9.
7.4.4 MODULATION DISPLAY CIRCUIT.
The modulation display circuit and moving bar LED display provides a visual indication of the modulation
percentage. A sample of the audio signal is input to gain switch amplifier U1B and automatic ranging amplifier
U1C. Gain switch Q7 is normally closed for high levels of audio signal.
With Q7 closed, U1C operates as an inverting unity gain amplifier. The output of U1C is applied to a precision
rectifier and meter ballistics circuit. This circuit consists of interated circuit U2, diodes D3 and D4, and transistor
Q1 and associated components.
The positive excursions of the signal at the output of U2A are applied to buffer U2B through diode D3. The
negative excursions are applied to buffer U2C through diode D4. The output of U2B and U2C are routed to
U2D which differentially amplifies the full-wave rectified signal.
The output of U2D is applied to current amplifier Q1 which transfers the positive charge on capacitor C12 to
C13 through resistor R36 and diode D24. The rate at which the charge is transferred is determined by R36. C13
discharges through R37 at a slower rate to provide the display with a gradual decay time and a rapid rise time.
The signal at capacitor C13 is routed to display drivers U19, U20, and U21 through buffer U1D and 100%
calibration control R41. Each display driver contains a resistive ladder network and comparator circuits which
sequentially activate output lines in direct proportion to the input voltage. Integrated circuit U17, resistors R91,
R93, and R95 provide a reference voltage for the display drivers.
The output lines of the display drivers are connected to LED displays DS9, DS10, and DS11 which illuminate
when the lines are activated. An output line from U20 is routed to one shot U18 which generates a one second
pulse to illuminate the 100% LED.