9/15/06
888-2586-001
4-43
WARNING: Disconnect primary power prior to servicing.
Section 4 Overall System Theory
Platinum Z16HD+
NOTE:
This controller number can be checked by pressing [HOME, MORE, CONFIGU-
RATION, C, B]. The actual DAC_APC_REF output voltage APC_REF can be
metered at TP8 or in the Diagnostics Display by pressing [METERING, C, B].
The output at U5-7 is the difference between the forward power sample and the
APC_REF voltage. This difference can be measured at TP3 on the Master Controller
and is called the APC voltage. R13 and R102 divide this voltage down for display on
the Transmitter LCD Display on the right side of the controller. The APC voltage is not
the same as the APC_REF voltage. The dipswitch, S1-10, is present to allow the APC
loop to be opened for troubleshooting. This APC voltage is now sent back to the Life
Support Board (Schematic, sheet [3,B8]) and is called APC.
If the Master Controller is operational, then the APC signal will pass through to U5-4
which will in turn pass the signal if there are no System Mutes present. Due to the low
impedance of the circuit, the Manual PWR REF pot R25 has little or no effect on the
circuit. The gate bias on the RF PA/IPA amplifiers is -18V for OFF and -0.6V for ON.
Changing the RF source output will increase or decrease the IPA output which will then
proportionately increase or decrease the output of the PAs.
EXAMPLE:
The following is an example of how the entire loop would work. For our example the
power output of the transmitter goes down due to a failed PA. This would decrease the
output of the forward power directional coupler and the voltage at the input to the
difference amp at U5-6 on the Master Controller Board. Since U5 has almost infinite
gain, the loop will try to force the forward power sample input to U5 to be the same as
the APC_REF input. This will increase the APC voltage at TP3 and on the front panel
APC reading. The increased APC voltage will pass through the U5 analog switches (on
the Life Support Board), then is sent to the RF Source, increasing its output. This RF
drive to the IPA then increases the IPA output. More drive to the PAs will increase the
transmitter RF output to compensate for the failed PA. Conversely, if the RF power
output were to increase, the APC loop voltage would be reduced, lowering the IPA and
PA output.
4.8.1.2.1 Manual Power Control
It is possible to shut off the APC by opening dip-switch S1-10 (Open = OFF) on the
Master Controller Board. When S1-10 is opened, MANUAL PWR REF R25 on the
Life Support board controls the transmitter power output. R25 also serves as the power
control for Life Support Mode which means the Master Controller Board has failed. If
the Master Controller fails, U5 pins 1-2 are opened, removing the increased APC drive
from the IPAs, breaking the APC loop. In Life Support Mode, R25 is set to operate the
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