Specifications

Section Q
Frequency Control Board
Q.1 Introduction
This section covers the Frequency Control board. Topics include
function, location, block diagram description, detailed circuit
description, troubleshooting, removal/replacement, and align-
ments.
NOTE: Parts List for this board is in Section VII.
Q.2 Function
The Frequency Control board is basically a control, metering,
and status panel for the three frequency transmitter. It provides
front panel control of the transmitter frequency, mode of opera-
tion, and other fine adjustments of transmitter tuning and load-
ing. Status indicators are used for reporting of frequency mode
and fault status, while multimeters indicate servo voltages re-
quired for tuning and loading.
Q.3 Location
The Frequency Control board is located behind the left front PA
compartment door. (SEE VIEW 24)
Q.4 Block Diagram Description
Refer to Sheet 1 of theschematic for the FrequencyControl board
839-7930-501 for the following discussion.
Q.4.1
Frequency Control Section
The Frequency Select Switches do not actually reside on the
board. Their BCD outputs are connected from the 3F Controller
to the board and passed as the Frequency Select Data for the
Synthesizer Interface board. The BCD frequency information is
encoded by the Frequency To Band Encoder PAL into Band
Select Data for use on the Frequency Control Interface board for
switching relays, and servo reference voltages.
Q.4.1.1 Normal Mode
The transmitter operates normally at the desired frequency with
all transmitter power modes available for operation.
Q.4.1.2 Frequency Change Mode
In this mode the transmitter is interlocked off and all frequency
adjustments are activated such as the frequency adjustment and
servo controls.
Q.4.2
Indicator Logic
The mode control information and Frequency Control Fault
inputs are connected to the LED Indicator Logic, which controls
the Tune Mode Indicator LED Drivers and the Enables for the
Fault Status Indicator LED Drivers.
The Tune Mode Indicator LED Drivers are used to illuminate the
proper mode LEDs.
The Frequency Control Fault inputs are applied to the Fault
Status Indicator LED Drivers and in conjunction with the En-
ables, allow these faults to be displayed when applicable.
Q.4.3
Meter Circuits
Two identical Multimeters are used for indicating the TUNE and
LOAD servo parameters simultaneously during the tuning proc-
ess. The two parameters measured are the servo Reference volt-
age and the servo Position Feedback voltage.
The Multimeter Switch Logic uses the mode information to
Enable the LED Displays and to control the Multimeter Auto
Switch that switches between the two servo samples. An addi-
tional function of the circuit is to switch the servo multimeters
to the servo reference samples at any time.
The TUNE Multimeter may also be used along with the Mul-
timeter Select Switch to measure Servo Supply Voltages and
Drive Chain Meter Samples.
Q.4.4
TUNE And LOAD Servo Control
The Raise/Lower fineadjustments of the servoson the Frequency
Control Interface board can be controlled by front panel center
off toggle switches on this board.
Q.4.5
Power Supplies
+22VDC, -8VDC, and +8VDC are regulated down to +15VDC,
-5VDC, and +5VDC respectively to power circuits on this board.
The +5VDC supply is monitored by the Power Supply Fault
Detector, which will generate a Supply Fault if the supply be-
comes defective.
Q.5 Detailed Circuit Description
Refer to the schematic diagram for the Frequency Control board
(839-7930-501) for all descriptions in this section.
Q.5.1
Mode Control Section
In order to provide a means to change frequency both quickly
and in as foolproof a manner as possible, modes of operation are
switch selectable in order to provide the proper transmitter
operation for the different phases of frequency change.
NOTE
The following is a description of what functions are active during
the different modes of operation.
Q.5.2 Normal Mode
The transmitter operates normally at the desired frequency with
all transmitter power modes available for operation.
Q.5.2.1 Frequency Control
No servo adjustments are active and the frequency and band
information cannot be changed even if the front panel Frequency
888-2339-002 Q-1
WARNING: Disconnect primary power prior to servicing.