b. Inhibit circuit U21 pins 4, 6, and 8, U20-3, and U63-3.
The “Inhibit” input is the “Overdrive Inhibit” from the
Controller turn-on/turn-off logic. The “Inhibit” logic:
1. Inhibits Air Flow Fault sensing when the transmitter is
OFF, during turn-on, and for a few seconds after turn-
on to allow air flow to be established.
2. Turns the “AIR LED” OFF for approximately 20 seconds
after the PA turns on. This prevents a GREEN indication
from being displayed until air flow is established.
c. Status Indicator latch and indicator drive circuits U34-11,
U35-5, U62 pins 8 and 11, U54 pins 8 and 10.
d. Status indicator “Inhibit” gates U62 pins 8 and 11. These
gates turn off the ColorStat™ indicator for a short time
after initial turn-on.
Q.5.2.3.1
Reduced Air Flow
If reduced air flow is detected by circuits on the Driver En-
coder/Temp Sense Board, J5-6 will go to logic HIGH. This will
force the output of U60 HIGH and illuminate the RED segment
of DS22 through U62-11 and U54-8. The combination of the
RED and GREEN segments will produce an AMBER indication
on the ColorStat™ panel. This provides visual indication of a
developing air flow problem. The transmitter will operate nor-
mally under this condition, and no fault is triggered.
Q.5.2.3.2
Insufficient Air Flow
The output from the airflow switch U17 on the Driver En-
coder/Temp Sense Board is logic HIGH for a fault. U20-4 is the
output from the airflow switch and the other input is an “Inhibit-
L” input if the transmitter is OFF and for 20 seconds after
turn-on.
The Inhibit-L at U20-5 will force the output LOW even if a fault
occurs. When the Inhibit is removed and pin 5 goes HIGH, a
normal air flow logic LOW signal from U17 holds U20-4 LOW,
and an air flow FAULT-H causes U20-6 to go HIGH. The U20-6
FAULT-H output goes to Type 1 Fault gate U32 and to the status
indicator circuit.
Q.5.2.3.3
“Air Interlock” Status Indicator Circuit
The Status Indicator circuit consists of Reset Retrigger AND
gate U34-11, latch U35-5, inhibit gates U62-8 and U62-11,
indicator drivers U54-8 and U54-10, reduced air flow gate U37,
and AIR indicator LED DS22.
When a FAULT is latched, the Q output of U35 is HIGH and is fed
through U37 to U62-13. The output of U62-11 is LOW and is
inverted to a HIGH by U54-8, which illuminates the RED section
of indicator DS22. The LOW NOT-Q output turns off the green
section of DS22. The LOW NOT-Q output is inverted by U54-6
to provide an AIR FAULT-H logic signal to the External Inter-
face.
Q.5.2.3.4
Inhibit “Air Interlock” Status Indication (Gates U62
pins 8 and 11)
When the transmitter is first turned ON and the Overdrive Inhibit
is released, the “Inhibit” logic in the Air Flow circuit generates
a 20 second logic LOW pulse which goes to U62-12 and
U62-10. This logic LOW pulse holds both NAND outputs
HIGH, preventing any status indication (either green or red).
Q.5.2.3.5
Inhibit Logic
The inhibit logic prevents an air flow fault from being sensed
for 20 seconds after transmitter turn-on, to allow air flow to be
established, and also turns off the Air Interlock status indicator
during this time. Air flow fault circuit “inhibit” logic includes
delay circuit U21 pins 4 and 6, gate U20-3 to provide an “Inhibit
fault sensing” signal, invertor U21-11, and gate U63-3 to pro-
vide an “Inhibit indication” signal. The Inhibit Logic has one
input and two outputs:
a. INPUT: “Overdrive Inhibit-L,” from the turn-on/turn-off
logic on the Controller. If the transmitter is OFF this input
is logic LOW; approximately 1 second after the begin-
ning of the turn-on step-start cycle the OVERDRIVE
INHIBIT goes HIGH and releases the inhibit.
b. OUTPUT: “Inhibit Air Fault Sense-L,” which inhibits Air
Interlock Fault sensing. When the transmitter is OFF
U20-3, is LOW. Approximately 20 seconds after the
OVERDRIVE INHIBIT is released, the “Inhibit Air Fault
Sense” is released and goes HIGH.
c. OUTPUT: “Inhibit Indicate-L.” This output, from gate
U63-3, is LOW for 20 seconds after the OVERDRIVE
INHIBIT is released, then goes HIGH. The “Inhibit Indi-
cate” turns the AIR Interlock indicator OFF for 20 seconds
after the PA Power Supply is energized. Delay circuit
U21-4/8 provides a “delay on - fast off” function, and
operates as follows:
1. When the transmitter is OFF, the delay circuit input
(Overdrive Inhibit) is LOW, invertor U21-6 is HIGH,
capacitor C71 is charged, and inverting Schmitt trigger
U21-4 is LOW.
2. When the “OVERDRIVE INHIBIT” is released and
goes HIGH, U21-6 goes LOW and capacitor C71
begins discharging through R99. After approximately
20 seconds, the voltage across the capacitor drops
below the threshold, and U21-4 goes HIGH. As long
as the transmitter is ON, U21-4 remains HIGH.
3. Diode CR9 provides a “fast off” function. The OVER-
DRIVE INHIBIT goes LOW when the transmitter
turns OFF and U21-6 goes HIGH. The logic HIGH
charges capacitor C71 through CR9 and R96.
Q.5.2.3.6
Air Fault Sense Inhibit
Gate U20-3 generates the “Air Fault Sense Inhibit” logic signal.
When the transmitter is OFF, the OVERDRIVE INHIBIT and
Figure Q-3. Latched Fault Status
Indicators, Simplified Diagram
DX-25U
Q-8
888-2297-002
Rev. R: 11-11-96
WARNING: Disconnect primary power prior to servicing.
