AR 10044005, Operating And Service Manual

Page: 58 / 72

Model 5000A225A
44 Rev B
3.4.3 Automatic Level Control Circuits
This section describes the operation of the Automatic Level Control (ALC) circuit board. Refer to schematic
diagram number 10023927,
Schematic, Digital ALC Board .
The ALC board performs the following general functions:
•
It limits the RF drive level to the amplifier stages and sounds an audible alarm when the amplifier’s
Forward or Reflected power levels try to exceed preset levels.
•
It sends a fault signal to the Digital Control Panel (DCP) if the limiting previously described fails to
control the amplifier’s Forward or Reflected power levels. This fault signal ultimately inhibits the
amplifier.
•
Allows the user the means to level at a set output power level.
3.5 FAULT DETECTION CIRCUITS
This section describes the function and theory of the Model 5000A225A’s fault detection circuits.
The driver power module A10 is monitored for over-temp fault using a thermal switch. In the event of an
over-temp, the PS2 power supply will be shut down so no DC is supplied to the A10 module.
The driver power module is also monitored for current faults. In the event of an over-current (OC) or under-
current (UC), the gain inhibit line to the module will be inhibited but the PS2 power supply will be active so
troubleshooting is possible.
Faults from the MPA’s are transmitted to the DCP by the Switch Breakout Board (SBB), A6 in the MPA. The
SBB assembly processes fault information from all four RF amplifier modules within the MPA. The faulty
module location is displayed, and a red LED indicator lights on the module at fault. There are four LED
indicators on each bias board, one for each power transistor.
Note that after a fault condition has been invoked, the circuit breaker and DCU circuit breakers must be left
on to keep the temporary memory active, until all faults can be manually recorded for diagnostic purposes.
Faults may be recorded by the host system if the host software is written to respond to fault conditions. Fault
conditions may be queried at any time during normal operation of the 5000A225A.
Detected fault signals are recorded in temporary (volatile) memory before the amplifier control circuits act to
protect the amplifier, sometimes resulting in RF inhibit or shut down. In some cases, inputs are read multiple
times to prevent a transient signal from causing an unwarranted action. Note that after a fault condition has
been invoked, the circuit breaker CB1 must be left on to keep the temporary memory active, so that all faults
can be manually recorded for diagnostic purposes. Faults may be recorded by the host system if the host
software is written to respond to fault conditions. Fault conditions may be queried at any time during normal
operation of the amplifier.
3.5.1 Thermal Faults
Each of the 500 watt modules in the MPA contains thermal sensor switches. In the case of a thermal fault, the
line will go high. The control panel displays the module designator and
TH , and the main power supplies
will be inhibited to allow the modules to cool down.