P.5.5
PA Turn-off (U53-3, U52-6, and S2)
The PA Turn-off circuit generates a logic LOW output at U53-3.
This is one input to the Modulation Encoders through the LED
Board that turns the PA Modules OFF by clearing all latches.
Refer to SECTION Q, LED Board, and SECTION L, Modula-
tion Encoder, for descriptions of PA turn-off circuits on those
boards.
Refer to the bottom of sheet 1 of the Controller Schematic, 843-5400-
091, in the Drawing Package for the following discussion.
P.5.5.1
Gate U53-3
If either input pin 1 or 2 to gate U53-3 is logic LOW, the output
will be a “PA OFF-L” signal. If BOTH inputs to gate U53-3 are
logic HIGH, the output will be HIGH. Inputs to Gate U53-3 are:
a. At pin 1: EXTERNAL PA TURN-OFF (active LOW),
from the External Interface, and PA OFF (active LOW)
from PA OFF switch S2.
b. At pin 2: PA OFF (active LOW) signal from gate U52-6.
P.5.5.2
“PA Off” Gate, U52-6
If any one or more inputs to U52-6 are HIGH, the output will
be LOW, and a “PA OFF-L” signal will always appear at U53-3.
If all three inputs to U52-6 are LOW, output U52-6 will be HIGH
to generate a “PA OFF” signal.
P.6
Power Control Logic: Circuit
Description
Refer to the Controller Schematic, 843-5400-091, in the Draw-
ing Package. The Power Control Logic generates a “Turn On
Command” to the Turn-0n/Turn-Off control logic and selects
the correct BCD data for the selected power level.
P.6.1
Command Inputs
Command (Control) Inputs are shown in the upper left part of
Sheet 1 of the Controller Schematic Diagram. Figure P-4 is a
simplified diagram of a Command Input circuit.
When a Command Input is active it generates a logic LOW input
to the Switch Debounce integrated circuit, U9.
P.6.1.1
Local Control Inputs
Each Local Control input is from the front panel switch on the
Switch Board/Meter Panel assembly. On the Controller, the six
local control inputs go to the four sections of transistor array
Q7, and to Q6B and Q6-2/6.
Each local control input drives the transistor through a 10K Ohm
series resistor and a pull-down resistor to ground. When the
front panel switch is open, the pull-down resistor holds the
transistor OFF. When the switch is depressed, +15 Vdc is
applied from the switch to turn the transistor ON and the
collector goes LOW.
P.6.1.2
Extended Control Inputs
Each extended control input comes from an opto-isolator on the
External Interface. A REMOTE input turns the opto-isolator ON
and pulls the collector line to ground (unless the LOCAL/RE-
MOTE switch is in the LOCAL position). The opto-isolator
output is paralleled with the corresponding Local Control input
transistor. When it turns on it pulls the input to the switch
de-bounce IC or the corresponding input to OR gate U58 LOW.
P.6.1.3
Fault-induced Inputs
Three transmitter “Fault” conditions provide power level “Com-
mand” inputs. Each “Fault” condition turns on a transistor in
parallel with the Local Control input and Extended Control
input transistors, so that a “Fault” induced command will also
pull the corresponding switch de-bounce IC input LOW. Fault-
induced commands include:
a. VSWR/TEMP INDUCED LOWER COMMAND. A
Logic HIGH input from the VSWR/TEMP Fault circuits
turns on Q5-1.
b. TYPE 1 FAULT INDUCED OFF COMMAND. Either a
“TYPE 1 FAULT-H” signal from the LED Board or an
Interlock Fault will cause the output of OR gate U51-8 to
go HIGH and turn transistor Q5-7 on.
P.6.2
Switch De-bounce (U45)
The Switch De-Bounce IC includes six independent “contact
bounce eliminator” sections and an internal “clock” oscillator.
Each input is pulled “HIGH” by an internal pull-up resistor to
the +5 Vdc supply. A command pulls the input LOW to activate
the input. The de-bounce IC is used to ensure a stable logic
output from the input circuits.
P.6.2.1
Internal “Clock” Oscillator
The oscillator frequency is approximately 200 Hz and is set by
the 0.01 uf capacitor connected between U45-7 and U45-9. The
clock output is also available at pin 9, and is buffered by U54-3
for use in other sections of the power control circuits.
P.6.2.2
“Contact Bounce Eliminator” Operation
Each section of the MC14490 requires a “clean” input (contact
“bounce” has stopped) for 3 to 4 clock cycles before the output
can change state. Any “Command” input must therefore be held
LOW for at least 20 milliseconds before the contact bounce
eliminator provides a command (logic LOW) to the rest of the
circuit.
P.6.3
Priority Encode/Decode
The Priority Encode/Decode circuit ensures that if two com-
mand inputs occur at the same time, only the one with the higher
priority will be executed. An “OFF” command has the highest
priority, and a “LOW” command has the lowest. Command
priorities, from highest to lowest, are as follows:
a. OFF ...... Highest priority
b. LOWER
c. RAISE
d. HIGH
e. MEDIUM
f. LOW ..... Lowest priority
An “OFF” command will override any other command.
Section P - Controller (A38)
Rev. S: 05-02-97
888-2297-002
P-7
WARNING: Disconnect primary power prior to servicing.
