Driver Amplifier modules D5, D9 and D10 can be selected
during factory test to be ON or OFF by JP1, JP2 and JP3. Some
frequencies do not require all 13 Driver Amplifier modules.
Line driver U1-11 controls the SPARE DRIVER D6 and line
driver U2-6 controls the AUTO DRIVER D7. The SPARE
DRIVER switch S1 is normally in the OFF position. The AUTO
DRIVER switch S2 is normally in the ON position.
S.2.1.1
Auto Spare Control Circuitry
The RF drive level to the 64 PA amplifiers is sampled and
converted into a “CVDC” signal. The “CVDC”
signal is used as the RF drive reference for the Driver Supply
Regulator and for the Auto Spare Control circuitry. The Control
+VDC voltage can be monitored on the RF MULTIMETER on
the inside of the Driver Compartment door.
The AUTO DRIVER D7 is used as a “coarse” drive adjustment.
If the RF drive level to the PA amplifiers decreases, due to the
failure of a Driver Amplifier or a decrease in AC line voltage, the
CVDC signal will decrease. The Driver Supply Regula-
tor will increase the drive by raising the B+ voltage to D8A and
then to D8B. If the Driver Supply Regulator increases the B+
voltage to both D8A and D8B to maximum (+115 VDC), and the
RF drive is still not at the proper level, the Auto Spare Control
circuit will turn D7 ON.
When D7 turns ON, the Driver Supply Regulator will reduce the
B+ voltage to D8A and D8B to keep the RF drive within the
correct range. The Driver Supply Regulator will then continue to
regulate the RF drive level by adjusting the voltage to D8. The
D8A and D8B voltage can be monitored on the RF MULTIME-
TER on the inside of the Driver Compartment door.
Comparators U3-8 and U3-10 form a threshold window to deter-
mine when D7 is ON or OFF. Driver Threshold adjustment R19
sets the ON threshold and Driver Threshold Reset R17 sets the
OFF threshold. When the Q output of U4 is HIGH, “set”, D7 is
ON. When the Q output of U4 is LOW, “reset”, D7 is OFF. The
AUTO DRIVER LED DS1 will illuminate then the Auto Driver
is operating.
During normal operation, the “CVDC” signal is above
the Driver Threshold ON level at TP-2 and below the Driver
Threshold Reset (OFF) signal at TP-1. Therefore, U3-13 is LOW,
U3-14 is HIGH, and U8-6 is LOW. This will “reset” U4-5 Q
output (LOW) and cause U2-6 to go HIGH. This will turn D7
OFF.
If the “CVDC” signal falls below the Driver Threshold
ON reference at TP-2, U3-13 goes HIGH and U8-6 goes HIGH.
This will “set” U4-5 Q output HIGH and cause U2-6 to go LOW.
This will turn D7 ON.
If the “CVDC” signal rises above the Driver Threshold
Reset (OFF) reference at TP-1, U3-14 goes LOW and U8-6 goes
LOW. This will “reset” U4-5 Q output LOW and cause U2-6 to
go HIGH. This will turn D7 OFF.
Figure S-1. Driver Encoder Block Diagram
Buffer Amplifier Control Functions
DX-25U
S-2
888-2297-002
WARNING: Disconnect primary power prior to servicing.
