Specifications

WARNING
ENSURE THAT THE TRANSMITTER IS TURNED OFF AND ALL
PRIMARY POWER IS TURNED OFF AT THE WALL DISCONNECT
SWITCH BEFORE OPENING ANY DOOR OR PANEL. BEFORE
REMOVING PANELS OR OPENING DOORS, VERIFY THAT THE
RF AMP POWER SUPPLY IS DISCHARGED BY CHECKING
“PA+VDC” ON THE FRONT PANEL MULTIMETER. USE A VOLT-
METER TO VERIFY THE POWER SUPPLIES HAVE BEEN DIS-
CHARGED PRIOR TO TOUCHING ANY COMPONENTS.
b. Check for open fuses on the Buffer Amplifier. If open
fuses are found, replace and troubleshoot the Buffer Am-
plifier.
6.4.2.3 No Buffer Amplifier Power Supply
a. Use the Driver Multimeter to measure the Buffer Voltage
during the step-start sequence. During step-start there
should be a +20-45VDC signal.
1. If the supply is not present, troubleshoot the +60VDC
power supply.
6.4.2.4 No Buffer Amplifier RF Input
a. With an oscilloscope, determine that the waveform on
TP5 of the RF Interface board is present and at the correct
frequency.
b. With an oscilloscope, look at the input to the Buffer
Amplifier on the ungrounded end of R16.
1. The level should measure 4-4.5Vpp.
2. If not refer to the overall diagram to troubleshoot the
circuit back to the RF Interface board.
6.4.3
Predriver/Low Drive
If these Control front panel LEDs are illuminated RED,it would
indicate that the RF drive level to the Driver stage is low.
6.4.3.1 Select Predriver B
The transmitter is equipped with two Predrivers. To select B:
a. Move S1, Predriver Select Switch, on the Driver Encoder
to the B position or provide the correct control input.
(Note that the Buffer and Predriver switch together).
b. Turn the transmitter on again, and observe the Control
front panel.
6.4.3.2 Defective Predriver A
a. If the transmitter returns with no fault, refer to the Trou-
bleshooting section for the RF Amplifier.
NOTE
The transmitter can be operated normally with Predriver B, until
time can be scheduled to continue troubleshooting Predriver A.
WARNING
ENSURE THAT THE TRANSMITTER IS TURNED OFF AND ALL
PRIMARY POWER IS TURNED OFF AT THE WALL DISCONNECT
SWITCH BEFORE OPENING ANY DOOR OR PANEL. BEFORE
REMOVING PANELS OR OPENING DOORS, VERIFY THAT THE
RF AMP POWER SUPPLY IS DISCHARGED BY CHECKING
“PA+VDC” ON THE FRONT PANEL MULTIMETER. USE A VOLT-
METER TO VERIFY THE POWER SUPPLIES HAVE BEEN DIS-
CHARGED PRIOR TO TOUCHING ANY COMPONENTS.
NOTE
The power supply for the Predrivers is fused on the Buffer Am-
plifier. F1 supplies Predriver A and F2 supplies Predriver B.
b. Check for open Predriver supply fuses on the Buffer
Amplifier. If open fuses are found, replace the fuses and
troubleshoot the Predriver.
6.4.3.3 No Predriver Power Supply
a. Use the Driver Multimeter to measure the Predriver Volt-
age during the step-start sequence. During step-start there
should be a +90-115VDC signal.
b. If the supply is not present, troubleshoot the +115VDC
power supply.
6.4.3.4 Observe DS3
a. If DS3 on the Predriver is not illuminated GREEN during
the step-start sequence:
6.4.3.5 No Predriver RF Input
NOTE
Refer to “Measuring RF Drive” at the end of this section for the
following discussion.
a. With an oscilloscope, determine that the RF drive wave-
form on the Predriver is present and at the correct fre-
quency.
1. If there is little or no RF drive, refer to the overall
diagram to troubleshoot the circuit back to the Buffer
Amplifier.
6.4.3.6 Loss of Turn-On Command
a. Measure J1-5 on the Driver Encoder, this point should be
at least -2VDC.
1. If it is not, refer to the Troubleshooting portion for the
Driver Encoder.
b. If the voltage is correct, use the overall wiring diagram
and the Driver Combiner schematic to check continuity
up to the Predriver input.
6.4.3.7 Failed Predriver Tuning Components
It is possible for one of the components on the Predriver Tuning
board to have failed and therefore de-tune the output. Failed
components like capacitors and inductors can sometimes be
identified by checking for abnormal heating after operating for
a short time. Refer to the Predriver Tuning board to test the relay
switching circuits and to the Frequency Control Interface board
to determine if the correct bandswitched outputs exist. If the
setting of the Predriver Tuning coil L1 has been adjusted, it can
be retuned for maximum Predriver Current on the Drive mul-
timeter when operating at 1600 kHz.
6.4.4
Low Drive
Low Drive Control front panel LED is illuminated RED.
This would alert you that the RF drive to the RF Amplifiers is
not sufficient.
The transmitter is equipped with AGC circuits on the Driver
Encoder, such that if Driver Amplifiers fail others will take their
place and RF drive level will be maintained. However, if too
many Drivers have failed it may not be possible for the Driver
Encoder to keep the RF drive level within the lower limit.
888-2339-002 6-3
WARNING: Disconnect primary power prior to servicing.