500W Power Amplifier Interface (A3J3)
Jack – Pin #
Function
2
6
32
J1 – 3
PS2 ENABLE: This output, sent to the Power Supply/Thermal Interface board
(A3PC2), is the control signal necessary to activate or deactivate 32V Power
Supply A3PS2. Control transistor Q1B provides an open (PS2 on) or short (PS2
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 PS2
ENABLE open/high provided by Q1B will be seen at the Power Supply/Thermal
Interface board input A3PC2J1-8 turning on power supply A3PS2 assuming an
overtemperature condition has not occurred as indicated by a high (open thermo-
stat) at A3PC2J1-8.
J1 – 1
GND: From J7-4
Video Detector Switch Interface (A9J1)
Jack – Pin #
Function
J8 – 1
VIDEO SENSE: A high or low indication for the presence or absence of video
programming is delivered to this input from the Video Detector Switch (VDS)
TALLY jack. With video present at INPUT A9-A of the VDS, an open is sent
from A9J1-NO to J8-1 and is looped to J3-5 placing a high on the Exciter’s
Control/Interface gate A2PC4U2C-10. If a loss of video occurs, a ground
appears at A9J1-NO forcing A2PC4U2C low at pins 10 & 8. This low appears at
AMP BIAS CONTROL input J3-3 from A2PC4J4-3 deactivating power supplies
A3PS1/PS2 in the 500W UHF Power Amplifier drawer A3.
J8 – 4
GND: From A9J1-COM
Exciter Interface (A2J4)
Jack – Pin #
Function
J3 – 1
AMP STATUS: A power supply failure (U1B or U2B low), an overtemperature
condition (U1D low) or an output transistor failure (U1A or U2A low) occurring in
the 500W UHF Power Amplifier (A3) will result in a low at this pin. The resulting
lows at A2PC4U4A-3/U4D-11/U4C-8 are sent through A2PC4J8-10 to
IF/Converter switch A2PC1S2 which determines if the IF output AGC is active
(high) or fixed (low). With a low at A2PC1S2-6, pins 1 & 2, 3 are closed placing
a ground on A2PC1U18-3. This low forces PIN diodes PC1CR9/CR10 to
stabilize at the center of their attenuation range (
3dB). At the same time, the
low output of AND gate A2PC4U4C is passed to pin A2PC4J10-18 and on to
Exciter front panel AGC ACTIVE LED control transistor A2PC3Q6. Since the
low will not allow A2PC3Q6 to conduct, A2PC3DS6 will turn off indicating an
inactive output AGC. If the voltage was high, transistor A2PC3Q6 would forward
bias causing the LED to turn on, indicating the output AGC is active.