888-2408-002 4-29
WARNING: Disconnect primary power prior to servicing.
Overall System Theory
Rectifier Boards on the PA power supply transformers. All three voltages pass
through the rectifier boards and are sent to the Backplane Board to power all of the
controller PC boards.
4.5.4.1 Relays
There are three mechanical relays on the Low Voltage Power Supply Board
assembly A19. They are A19K1, A19K2 and A19K3. The relays are powered by
+12Vdc from the Life Support Board in the controller.
• A19K1 is activated when the transmitter is turned on and the
“CONTACTOR_ON” signal from the Life Support Board goes low. When acti-
vated, A19K1 supplies Phase A (or Neutral) to the coil of the AC mains contactor
K1 (and K3 in the Auxiliary cabinet for the single phase), which then supplies
AC to the PA power supply transformers.
• A19K2 is activated by the same “CONTACTOR_ON” signal and supplies Phase
B to the exciter(s). Note that this means the exciter(s) will not have power until
the transmitter is turned on.
• A19K3 is activated by the active low “FAN_SPEED_SELECT” signal from the
Life Support Board. A19K3 activates the fan speed select relay K2 mounted next
to the AC mains contactor on the cabinet wall. K2 is shown on the Overall Sys-
tem Block Diagram in the HIGH fan speed position. When A19K3 pulls in so
does K2 (not A19K2).
4.6 Cooling System Description
The transmitter is cooled by the single, two speed fan in the lower rear of the
transmitter. It uses a high volume, low velocity, air system. Air ducting for inlet air
should be well filtered and, if possible, at a slightly positive pressure. The exhaust
air ducting should cause very little or no back pressure due to the low velocity air
system. Air handling recommendations are shown on the Cabinet Outline Drawings
in the schematic package.
Upon transmitter turn on, the fan will run at high speed for one minute, then will
normally run at the low speed until a fault occurs or there is a significant increase in
temperature detected by the controller. The blower motor is a 2 speed, single phase
motor. Contactor K2 selects the fan speed and is controlled by the Master
Controller. The fan speed can also be manually set to HIGH speed or AUTO in the
Configuration Menus of the Diagnostics Display.
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