12/20/11
888-2595-001
4-5
WARNING: Disconnect primary power prior to servicing.
Section 4 Theory of Operation
ZX Series
The output of the line filters is supplied to the inputs or a series of power supply (PS)
modules plugged into the 8x PS interface board (see also 801-0203-531). The PS
modules convert AC mains power in the 190V - 264V range into DC power in the 43V
- 53V range up to 1250W (nominally 25A at 50V). The PS modules also produce 5V @
500 mA (output) to power the logic circuits for the amplifier chassis.
The +50V DC voltage from the PS interface board is distributed to DC cooling fans and
to one or more PA backplanes. The PA backplane acts as an interface to the PA module,
receiving DC power from the power supplies and communicating logic signals to the
transmitter controller board.
The transmitter controller also receives power readings from detectors on the RF output
assembly to drive the transmitter power control (APC) circuits and front panel power
meter.
The transmitter controller communicates to the outside world via the I/O filter PCB.
The I/O filter PCB contains RF filtering devices to prevent externally generated
interference and voltage spikes from damaging the transmitter.
4.5
PA Backplane
Consult drawing 801-0203-381
The PA backplane provides all of the necessary support functions to properly operate
the RF amplifiers contained on the PA module. These functions include a socket
connection with DC inputs and RF outputs and alarm detection with latched shutdown
for four different conditions:
a.
excessive reverse power at the PA output (>25W),
b.
excessive temperature at sensor at MOSFET mounting flange (>99C),
c.
excessive DC current into the PA module (>22A), or
d.
the PA module is physically removed from the socket.
The presence of a fault condition is indicated by a series of three red LEDs located just
behind the upper right-hand corner of the PA module when installed in its position.
4.5.1
PA Reverse Power Alarm
A reverse power RF sample derived by frequency compensated diode CR2-C24 (CR1-
C2) is amplified by temperature compensated amplifier U1A (U1B). A diode-or circuit
formed by CR4E and CR4F passes along the higher of the two reading to fault
Summary of Contents for ZX2500
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Page 6: ...MRH 2 888 2595 001 12 20 11 WARNING Disconnect primary power prior to servicing...
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