indicating normal drive in a PA module. If the sample goes above
the reference set by R101, U6 pin 1 will go low, indicating an
overdrive fault.
* Monitors output reflected power, and protects the module from
elevated load VSWR. Output reflected samples from the output
directional coupler assembly are received at J1-22. The VSWR
fault threshold is established by R8. If the voltage at U6 pin 5,
determined by the reflected power, is greater than the voltage at
pin 4, then pin 2 will go low, indicating a VSWR fault.
* Monitors the DC power supply voltage, and protects the
module from high and low voltage extremes. The DC supply is
sampled at J1-23, and is scaled down by R48, R47, and R42. A
maximum voltage reference is established by the +15 Volt regu-
lated supply, R43, and R44. If the sample exceeds the reference,
U7 pin 1 will go high, indicating an overvoltage fault.
Likewise, a minimum voltage reference is established by R45
and R46. If the reference exceeds the DC supply sample, U7 pin
2 is driven high, indicating an undervoltage fault.
* Monitors ISO voltage samples of the quarter modules, protect-
ing the amplifier from damage due to imbalances between the
two halves of a quarter module. The ISO voltage samples are
combined by a OR circuit and collected at J1-3, 4, 16 and 17 on
the controller board.
A reference is established by R38 and R81. If the ISO voltage
sample exceeds the reference, U6 pin 13 is driven low, indicating
a fault.
* Monitors the temperature of the quarter modules, turning off
the amplifier if excessive temperatures are encountered. A volt-
age is developed on each module by the thermistor circuitry that
is proportional to the heat sink temperature. These voltages are
routed to the module controller board, J1-5, 6, 7 and 8. The
voltages are compared to a reference by comparator U13. If any
quarter module temperature voltage is lower than the reference,
the comparator output will go low. This switches the output of
the Schmitt trigger high.
*Enables the 50 Volts DC to the quarter modules by controlling
a pair of high-power switching FETs (“pass FETs”) located on
the module rear panel. If no faults are present, PAL U1 pin 12
sends a signal to U7 pin 8, which controls a circuit that turns on
the pass FETs, a pair of n-channel switching FETs. If a fault
condition occurs, the switching FETs are turned off.
The switched 50 Volts dc is reduced to 15 Volts by R39 and U10.
This 15 Volts is routed to each quarter module for bias circuitry
power.
The incoming 50 Volt DC power is switched on and off by the
pass FET assembly, controlling the application of 50 Volts to the
Quarter Modules. This switched 50 Volts is reduced to 15 Volts
by regulator U10. The +15 is supplied to each module to be used
for temperature sensing and FET biasing.
The logic will not allow the module to enable if a fault condition
exists, to protect the module from damage.
A.2.9
Module Status LEDs
Each module uses two front panel LEDs to display its current
operating status. The LEDs are driven by signals from the PALs
and U8 and U9, which are NAND gates configured as buffers.
The status can be interpreted from the LEDs as follows:
a. Steady Red - 50 Volts applied to the module, but the
module is not enabled. This will normally occur if a
module is removed and then reinserted in the slot.
The red LEDs will illuminate then fade out as the supply
capacitors discharge each time the transmitter is turned off.
b. 1/2 Green LED Illuminated - Module is enabled but little
or no RF drive is supplied to the module.
Driver modules, because of their low input drive level, do not
have a drive level indication. Thus, when a driver module is
enabled, both halves of the green LED are illuminated regardless
of drive level. This is the only difference between the PCM
systems on drivers and PAs.
a. Full Green LED Illuminated - A full green LED illumi-
nated indicates normal module operation. - Module is
enabled. Additionally, in PA modules, the presence of RF
drive is indicated.
b. No LEDs Illuminated - The 50 Volt DC power is not
reaching the module, or the module has been turned off by
pulling on the front handle (“mechanical disable”).
In some cases this could be the symptom of a module control
fault. If you have not disabled the module turn off the transmitter
momentarily while removing the module. This will prevent
possible arcing of the input connector pins if the module was in
fact on but not lighting any LEDs.
A.2.9.1
Red LED Fault Blink Codes
If a module fault occurs, the red light will “blink” on and off. The
number of blinks between pauses is the “blink code,” and is used to
determine the type of fault. The blink code is as follows:
a. 1 Blink - High VSWR condition at the module output.
b. 2 Blinks - RF input overdriven
c. 3 Blinks - An elevated ISO voltage resulted from an
imbalance between halves of a quarter module.
d. 4 Blinks - The power supply voltage applied to the module
is too high or too low.
e. 5 Blinks - The quarter module temperature is too high.
f. 6 Blinks - The pass FET transistors that switch the 50 Volts
to the quarter modules have failed.
A.3
Module Troubleshooting
CAUTION
Use extreme care when repairing or testing RF amplifier modules. Be-
cause they are capable of producing over 1000 Watts of output power,
serious RF burns can result from coming in contact with any high power
points inside the module while it is operating.
A-6
(888-2365-001) (888-2377-001) (888-2378-001)
10-16-95
WARNING: Disconnect primary power prior to servcing.
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