Assembly Instructions Chapter 4

4-6 kW UHF Translator Chapter 4, Circuit Descriptions
837B, Rev. 0 4-23
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 translator 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 switch
S2 in Auto, a low is applied to U5A, pin
2, and to U5D, pin 13. When U5A, pins
1 and 2, is low, its output at pin 3 goes
high. When pin 12 of U5D is high, the
output of U5D at pin 11 goes low.
When U5A, pin 3, is high, it biases on
Q20 and applies a pull-down enable to
the Operate switch. A low at U5D, pin
11, biases off Q19 and removes any
pull down to the Standby switch. As a
result of these actions, the translator is
switched to Operate.
4.2.7.4 Faults
There are four possible faults, video
loss fault, VSWR cutback fault,
overtemperature fault, and ALC fault,
which may occur in the translator and
are applied to the transmitter control
board. During normal operation, no
faults are sent to the board. The
overtemperature fault is connected to
the (A8-A1) thermal switch on the (A8)
2500W reject load for the translator.
Video Loss Fault
If a video loss occurs while the
translator is in Auto, the system will
change to the Standby mode until the
video is returned; at that point, it will
immediately revert to Operate. A video
loss fault applies a low from the ALC
board to the video fault input at J7-5
on the board.
With jumper W1 in place on J10, the
video fault is connected to LED DS9
and to Q16. The red Video Loss Fault
LED DS9 on the front panel will light.
Q16 is biased off and causes its drain
to go high. The high is wired to U5B,
pin 5, whose output at U5B, pin 4, goes
low. The low is wired to Q18, which is
biased off, and causes the drain to go
high. The high is connected to U3D, pin
12, which causes its output at U3D, pin
14, to go high. The high connects to
U5A, pin 1, and, if the translator is in
Auto, pin 2 of U5A is low. When pin 1 is
high and pin 2 is low, the output of U5A
goes low and reverse biases Q20,
shutting it off. The high at U5C, pins 8
and 9, causes its output at pin 10 to go
low. This low is connected to U5D, pin
12, and, if the translator is in Auto, pin
13 of U5D is also low. The lows on pins
12 and 13 cause the output to go high
and forward bias Q19. The drain of Q19
goes low and connects the coil in relay
K1, causing it to switch to Standby.
When the video returns, the video loss
fault is removed from the video fault
input at J7-5. With jumper W1 in place