connected between the Inverter/Driver input and P9-1 or 2, the
“Momentary Test” button can be depressed to turn that module
ON.
L.5 Troubleshooting
NOTE
Place P1 on the DC Regulator in the TEST position to enable the
B+ and B- supplies for the Modulation Encoder when the PA
Power Supply is not energized. Return P1 to NORMAL position
after troubleshooting.
L.5.1 Symptom: Suspected Faulty Modulation Encoding
L.5.1.1 Troubleshooting Suggestions
Faulty latches and other digital IC’s can be identified using a
voltmeter to check inputs and outputs. Typically, PA Modules
RF33 through RF55 are turned ON for 25 kW carrier. This can
be verified by the green LED indicators on the modules. For
100% positive peak modulation with a continuous sine wave, PA
Modules RF33 through RF79 should be turned ON.
L.5.2
Symptom: Red “PA O ff” Indicator Illuminated
L.5.2.1 Troubleshooting Suggestions
Check the ColorStat™ panel for other indications. Most causes
for a “PA OFF” indication will also cause a RED Fault indication
on the ColorStat™ panel. If there are no other indications, you
can check the logic inputs to PA Turn-Off gates to isolate the
source of the incorrect logic signal, then trace back to its cause
(which may be on another board). (Refer to the simplified
diagram of PA Turn-Off logic, Figure L-3, and to the Schematic
Diagram for PA Turn-Off logic).
Most causes of “PA Off” indications on the Modulation Encoder
will be traced back to “PA Off” signals from other printed circuit
boards. Failure of logic gates, inverters, or drivers can also cause
a “PA O ff” indication, and a logic probe or a voltmeter can be
used to check inputs and outputs of gates, inverters,or drivers for
HIGH and LOW logic level signals.
Additional causes fora“PA OFF” indicationinclude theExternal
PA OFF input from an interlocked component or from the PA
OFFswitchS5ontheController.
L.5.3
Symptom: Cable Interlock Indication
NOTE
A Cable Interlock condition will prevent an ON command from
being generated. Because the regulated voltages to the Modula-
tion Encoders are muted on the DC Regulator until an ON com-
mand is generated, the DS1 Cable Interlock LED indicators will
not be active. To activate the regulated voltages to the Modula-
tion Encoders, place P1 on the DC Regulator in the TEST posi-
tion. Return P1 to the NORMAL position after troubleshooting.
L.5.3.1 Possible Cause: PA Module Removed or Not Prop-
erly Inserted in Socket
Check PA Modules to make certain that all are installed and fully
inserted in their sockets.
L.5.3.2 Possible Cause: Defective component on PA Module
Once the Cable Interlock fault is isolated to a group of eight
modules by using thechart on Sheet 4 ofthe Modulation Encoder
Schematic, 839-7855-174, swap each module out one at a time
to identify the defective module.
Figure L-1. Modulation Encoder,
Simplified Output Circuit
Section L - Modulation Encoder (A37)
Rev. T2: 06-27-97 888-2297-002 L-5
WARNING: Disconnect primary power prior to servicing.
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