Specifications
Section VIA
Emergency Operating Procedures
6.1 Introduction
The following section is intended to make the maintenance
personnel aware of some of the bypass modes of operation that
are possible in the transmitter. If certain failures occur, it is
possible to temporarily bypass the source of the problem and
remain operational at the highest possible power level until
proper maintenance can be performed.
6.2 RF System Bypassing
6.2.1 Synthesizer Interface Failure
6.2.1.1 Optional Synthesizer Interface Installed
If the transmitter is equipped with optional Synthesizer Interface
B A3, select B by moving S2 on the RF Interface to the B position
or providing the correct control input.
6.2.1.2 Optional Synthesizer Interface Not Installed
On the Synthesizer Interface board, it is possible to bypass the
Synthesizer.
6.2.1.2.1 External RF Input
If the Synthesizer fails, it is possible of feed in an External RF
Input. Two jumpers will have to be moved, before the BNC
connection is made:
a. Turn off the Main Breaker for the Low Voltage Power
Supplies.
b. Move JP2 from the Internal position of 1-2 to the External
position of 2-3.
c. Ensure that JP3 is in the correct position for the source
impedance used. JP3 2-3 for a 4.0-4.5 VP-P TTL level
input or JP3 2-1 for 0-50 dBm 50 Ohm input.
6.2.2
Buffer/Predriver Failure
The transmitter is equipped with two Buffer/Predriver Amplifi-
ers. Normally Buffer/Predriver A is selected for operation.
6.2.2.1 Select Buffer/Predriver B
To select Buffer/Predriver Amplifier B move S1 on the Driver
Encoder A7 to the B position or provide the correct control input.
6.2.3
Driver Amplifier Failure
6.2.3.1 Multiple Driver Failures
If the operation of the AGC circuit is not sufficient to maintain
the proper RF drive level, the transmitter will turn OFF due to a
Low Drive Fault. After using the Troubleshooting Section to
determine the location of the failed Drivers it is possible to:
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.
6.2.3.2 Change RF Amplifier/Driver Positions
They can be manually switched with the highest Big Step RF
Amplifiers. RF156 should be used first, RF155 second, and so on.
6.2.4
Big Step RF Amplifier Failure
FLEXPATCH
Flexpatch is a method of substituting a failed Big Step RF
Amplifier’s turn on/off control line with one of the Programma-
ble Big Steps. There are five Programmable Big Steps in the
transmitter, their locations are:
a. Left Compartment, the bottom left and right amplifier
slots. Normally programmed to be Big Steps RF 152(L)
by Modulation Encoder A29 andRF153(R) by Modulation
Encoder A28.
b. Center Compartment, the bottom left and right amplifier
slots. Normally programmed to be Big Steps RF 154(L)
by Modulation Encoder A27 andRF155(R) by Modulation
Encoder A26.
c. Right Compartment, the bottom right amplifier slot. Nor-
mally programmed to be Big Step RF156(R) by Modula-
tion Encoder A25.
These Programmable Steps are the five highest steps in the
transmitter. If they are substituted for lower steps, only a reduc-
tion in positive peak modulation will occur.
To substitute a failed step, the gold jumper for the step will have
to be removed and the switch positions on S7 and S8 will have
to be reset on the appropriate Modulation Encoder.
USING FLEXPATCH
a. Example 1 - Step 9 has failed.
The Modulation Encoder for this step is A29 (SEE VIEWS
14 & 21A for the following discussion).
1. The gold jumper for Step 9 is P3-7, as shown on the
right side of P3. Carefully remove this jumper.
2. Using the FLEXCODE chart, rotate S7 from 8 to 9 and
rotate S8 from 9 to 0.
3. Now the Step that was RF152 is effectively Step 9.
b. Example 2 - Step 133 has failed.
The Modulation Encoder for this step is A25 (SEE VIEWS
10 & 23 for the following discussion).
1. The gold jumper for Step 133 is P1B-8, as shown on the
right side of P1B. Carefully remove this jumper.
888-2339-002 6A-1
WARNING: Disconnect primary power prior to servicing.