Manual Chapter 3

500-Watt UHF Transmitter Chapter 3, Circuit Descriptions
425A, Rev. 0 3-18
3.1.8.2 Automatic/Manual Switch S2
K2 is a magnetic latching relay that
switches the operation of the transmitter
to Automatic or Manual using Auto/
Manual switch S2 on the front panel of
the tray.
When S2 is set to the Auto position, the
operation of the transmitter is controlled
by the fault circuits and will stay in
Operate even if Operate/Standby switch
S1 is moved to Standby. With S2 in Auto,
a low is applied to one coil in the relay
and this energizes and closes the
contacts. The closed contacts apply a low
to the green Automatic LED DS3; as a
result, DS3 is illuminated. The low from
the relay connects to U5A, pin 2; U5D,
pin 13; Q21; and Q23. When Q21 and
Q23 are biased off, this causes their
outputs to go high. The high from Q21
connects to the amber Manual LED DS4,
on the front panel, biasing it off, and to
Q22, biasing it on. The drain of Q22 goes
low and is applied to J8-7; this enables
any remote auto indicator connected to
J8-7. The low to Q23 biases it off and
removes the enable to any remote
manual indicator connected to J8-6.
When S2 is set to the Manual position,
the operation of the transmitter is no
longer controlled by the fault circuits; it is
controlled by Operate/Standby switch S1.
With S2 in Manual, a low is applied to the
other coil in the relay and this energizes
and opens the contacts. The open
contacts remove the low from the green
Automatic LED DS3 on the front panel
and causes it to not light. The high
connects to U5A, pin 2; U5D, pin 13;
Q21; and Q23. Q21 and Q23 are biased
on; this causes their outputs to go low.
The low from Q21 connects to the amber
Manual LED DS4 on the front panel,
biasing it on, and to Q22, biasing it off.
The drain of Q22 goes high and is applied
to J8-7; this will disable any remote auto
indicators connected to it J8-7. Q23 is
biased on and applies a low enable to any
remote manual indicator connected to J8-
6.
3.1.8.3 Automatic Turning On and Off of
the Transmitter Using the Presence of
Video
The transmitter control board also allows
the transmitter to be turned on and off
by the presence of video at the
transmitter when the transmitter is in
Auto. When a video fault occurs due to
the loss of video, J7-5 goes low. The low
is applied through W1, on J10, to Q16,
which is biased off, and to the red Video
Loss Fault LED DS9, on the front panel,
which will light. The drain of Q16 goes
high and connects to U5B, pin 5, causing
the output at pin 4 to go low. The low
connects to Q18, which is biased off, and
causes the drain of Q18 to go high. The
high connects to U3D, pin 12, whose
output at pin 14 goes high. The high
connects to U5C, pins 8 and 9, causing
its output at pin 10 to go low, and to
U5A, pin 1, causing its output at pin 3 to
go low.
With S2 set to Automatic, a low is applied
to U5A, pin 2, and to U5D, pin 13. When
U5A, pin 1, is high and U5A, pin 2, is low,
it causes the output at pin 3 to go low.
When U5D, pin 12, is low and U5D, pin
13, is low, it causes its output to go high.
When U5A, pin 3, is low, it biases off Q20
and removes any pull down to the
Operate switch. A high at U5D, pin 11,
biases on Q19 and applies a low enable
to the Standby switch that places the
transmitter in the Standby mode.
When the video signal is returned, J7-5
goes high. The high is applied to Q16,
which is biased on, and to the red Video
Fault LED DS9, which is extinguished.
The output of Q16 goes low and connects
to U5B, pin 5. If there is no receiver ALC
fault, U5B, pin 6, is also low; this causes
the output at pin 4 to go high. The high
connects to Q18, which is biased on, and
causes the drain of Q18 to go low. The
low connects to U3D, pin 12, whose
output at pin 14 goes low. The low
connects to U5C, pins 8 and 9, which
causes its output at pin 10 to go high,
and to U5A, pin 1. With Auto/Manual