888-2408-002
4-59
WARNING: Disconnect primary power prior to servicing.
Overall System Theory
4.7.6.2.2 Reflected Power
The reflected power sample enters the board at J3. It is detected by CR10 and
buffered by U1-1. The voltage at TP7 is directly proportional to the amount of
reflected power coming back to the transmitter from the antenna or transmission
line. This DC sample voltage is sent to the Master Controller, via J1-A19, for
VSWR protection and monitoring when the Master Controller is operational.
If the Master is not functioning (Life Support Mode), then the RFL PWR Overload
Adjust, R24 and comparator U3-2, will protect the transmitter from excessive
VSWR by shutting it off. R24 sets the reference voltage for U3-5, which is the
VSWR comparator for Life Support Mode. If the VSWR exceeds 150 watts
reflected in this mode the comparator will trip and U3-2 will go low. This is inverted
at U7-6 and becomes, LS_SYST_FAULT, which stands for Life Support System
Fault. This signal is sent to AND gate U6-1. U6-2 is connected to the
MASTER_NORMAL line. This line will be high only if the Master Controller has
failed, which is the case here for Life Support Mode. Therefore the
LS_SYST_FAULT will cause U6-3 to go high. Next, OR gates U33-3 and U33-6
will also go high, making U16-10 output high. This is connected to the RESET side
of latching relay, K4. When K4 resets, K4-14 will go low, which will send a low to
the Low Voltage Power Supply Board, via U16-12. The main AC contactor will
disengage and the transmitter will be shut off.
It is important to note that if the Master controller is working, then U6-3 would not
go high and therefore the LS_SYST_FAULT is not active. This is due to the fact
that the Master Controller has the primary responsibility for VSWR protection. This
circuit only has function when the Master Controller has failed and the transmitter is
running in the Life Support Mode.
4.7.6.2.3 IPA Current Fault
While in Life Support Mode, IPA Current overload protection is accomplished
using comparator U3-1 and IPA Current Fault Adjust, R23. R23 is set for a
conservative IPA current level. If the IPA current is too high, U3-1 will go low. This
is tied into the LS_SYST_FAULT circuit at U7-6 discussed earlier and will shut the
transmitter off.
Summary of Contents for Z5 CD
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Page 192: ...6 40 888 2408 002 WARNING Disconnect primary power prior to servicing Troubleshooting...
Page 194: ...7 2 888 2408 002 WARNING Disconnect primary power prior to servicing Parts List...
