500W Power Amplifier Interface (A3J3)
Jack – Pin #
Function
2
6
31
J1 – 7
+5V: From PS1J2-2
J1 – 6
POWER SUPPLY OK: This input is the status monitor line for the two 32V
Power Supplies (A3PS1/A3PS2) contained in amplifier drawer A3. This line
originates from the Amplifier Status Interface board at A3PC1J1-3 and is low
when both power supplies are operating normally, forward biasing transistor Q3
which supplies a high collector to U1B-4 & 5. The high output on U1B-6 will
make control transistor Q6 conduct turning on AMPLIFIER POWER SUPPLY
light DS2. If one of the power supply outputs drops below 28 volts, this line will
shift high shutting off power supply indicator DS2. Concurrently, a low will be
sent via U1C-8, U2D-11, U1D-11 and J3-1 to the Exciter’s Control/Interface
board at A2PC4J4-1. From here the signal finds the IF/Converter Output AGC
Control at PC1J6-10 from A2PC4J8-10, disabling the AGC so that the transmitter
can continue to operate at a lower power.
J1 – 4
THERMAL STATUS: This control signal is generated on the Power Supply/
Thermal Interface board (A3PC2) which monitors the thermostats fastened to
each 300W Amplifier heat sink (A3A1/A3A2) located in the 500W Power
Amplifier drawer. The circuit provides an open/high under normal amplifier
operating temperatures while supplying a short/low during overtemperature situ-
ations. With an open connected to base resistor R44, transistor Q9 is cutoff
extinguishing AMPLIFIER TEMPERATURE LED DS10. If one of the 300W heat
sinks becomes too hot (
175
(
F), opening its associated thermostat, the Thermal
Interface board will develop a short at R44 turning on Q9 and indicator DS10 as
notification that an overtemperature situation has occurred. Aside from the
appropriate power supply being deactivated, the low at R44 will shift the output
of gate U1D presenting a low at J3-1, the AMP STATUS output. As stated
previously, this signal is sent to the IF/Converter Output AGC Control via
A2PC4J4-1, A2PC4J8-10 and A2PC1J6-10 to disable the AGC circuit so that the
transmitter operates at a reduced power commensurate with an inactive
300 Watt Power Amplifier.
J1 – 2
PS1 ENABLE: This output, sent to the Power Supply/Thermal Interface board
(A3PC2), is the control signal necessary to activate or deactivate 32V Power
Supply A3PS1. Control transistor Q1A provides an open (PS1 on) or short (PS1
off) as dictated by op-amp U3 which receives its instructions directly from the
Exciter’s AMP BIAS CONTROL appearing at J3-3 from A2J4-3. Power supply
activation requires a high at U3-2 which will appear when the Exciter’s UHF
Synthesizer A2A2 is locked (A2PC4U1A high), when the OPERATE/STANDBY
switch is in OPERATE (A2PC4U1D-11 high) and when the VIDEO SENSE line
is high (A2PC4U2C high) indicating video present at the modulator. The PS1
ENABLE open/high provided by Q1A will be seen at the Power Supply/Thermal
Interface board input A3PC2J1-4 turning on power supply A3PS1 assuming an
overtemperature condition has not occurred as indicated by a high (open
thermostat) at A3PC2J1-5.