M.2.8
+5 VDC Supply
The DC Regulator fault sense circuitry is operated from a regu-
lated +5 VDC supply consisting of regulator U11. Unregulated
+22 VDC passes through the DC Regulator to the Modulation
Encoder (A37) for the cable interlock protection circuits. Zener
diodes CR26 and CR36 reduce the +22 VDC supply to approxi-
15 VDC at TP23. Diodes CR31 and CR37 ensure that
the fault detection circuitry will be active if either F1 or F4 opens.
Transient protection and clamping is provided by CR25.
M.2.9
-5 VDC Supply
A -5 VDC supply is used for the B- Reference Modulator circuit
and to power U10. Two separate -8 VDC unregulated inputs are
diode gated through CR12 and CR11 to regulator U12. This
allows for continued operation of the B- Fault Detector if either
F3 or F6 were to open. CR27 provides transient protection and
clamping should U12 fail.
M.2.10
Fault Detection Circuits
A problem on the DC Regulator will output either a B+ fault or
B- fault to the Controller (A38) and will illuminate the B- or B+
fault LED on the ColorStat™ panel. Either fault will inhibit a
transmitter ON command and prevent the PA Power Supply from
energizing.
The fault indicator LED’s on the DC Regulator are inhibited until
a “TXONEN” command is generated during turn-on. A
“TXONEN” command will cause U8-6 to go HIGH enabling the
B+ and B- fault gates and will also enable LED driver tri-state
inverter U7. To enable the fault gates and LED’s for troubleshoot-
ing purposes, P1 should be moved to the “TEST” position.
CAUTION
DO NOT LEAVE P1 IN THE TEST POSITION FOR EXTENDED
PERIODS OF TIME DUE TO LACK OF COOLING FOR THE REGU-
LATOR PASS TRANSISTORS.
M.2.11
B+ Fault Circuit
The B+ fault gate consists of U9 and U8. Any logic HIGH signal
on the input of U9 will cause the output at pin 1 to go HIGH. The
output of U8-11 will then go LOW. Any of seven individual fault
circuits gated together by U9 will trigger the B+ fault circuit.
These are:
a. Ambient Temp. Sensor
b. B+ Fault Detector “A”
c. +5V Detector “A”
d. +22V Detector “A”
e. B+ Fault Detector “B”
f. +5V Detector “B”
g. +22V Detector “B”
As the “A” and “B” circuits are identical, only the “A” circuits
will be described.
M.2.11.1
Ambient Temp. Sensor
The ambient temperature detector is an Airpax model 66F070
which trips at 70 Degrees C, +/-5 degrees. An ambient tempera-
ture fault will light DS5 and trigger B+ Fault gate U9.
M.2.11.2
B+ Fault Detector
IC U4 will produce a B+ Fault output if the B+ voltage drops
below 15% or rises above 10% of normal. Pin 7 (TP13) of U4
establishes the over-voltage threshold at approxi3.7
VDC and Pin 4 (TP16) of U4 establishes the under-voltage
threshold at approxi3.0 VDC.
M.2.11.3
+5V Detector
The +5 VDC detector monitors the supply used for the Modula-
tion Encoder (A37) logic circuits. This +5 VDC supply is derived
by placing a diode in series with the 5.75 VDC B+ supply on the
Modulation Encoder. A sample is then fed back to the DC
Regulator for the fault detection circuit. If the voltage at pin 10
of U5 falls below the reference at pin 11, pin 13 will go to logic
HIGH state and trigger the B+ fault gate.
M.2.11.4
+22V Detector
Unreg22 VDC is used on the Modulation Encoder (A37)
for cable interlock circuitry. The Modulation Encoder receives
it’s supply through F1 and F4 on the DC Regulator. The +22V
fault detector monitors this line and will output a logic HIGH on
U5-14 if the voltage at pin 8 of U5 falls below the reference at
U5-9.
M.2.12
B- Fault Circuit
The B- Fault Circuit consists of the B- Fault gate, B- Fault
Detector and B- Reference Modulator. The circuit will produce
a B- Fault if the modulated B- voltage drops below 10% of
normal or exceeds -6 VDC.
A sample of the B- output is brought into pins 4 and 7 of U5. A
reference voltage of approximately 1.7 VDC on U5-6 corre-
sponds to an over-voltage of -6 VDC. Pin 1 of U5 will go to logic
LOW under a B- over-voltage condition.
Because the B- voltage is a modulated supply, the under-voltage
reference at U5 pin 5 is also modulated with the same B-
pre-distortion signal seen at TP14. This -(Audio + DC) pre-dis-
torted signal is placed on a positive bias by U10. If the B- falls
below 10% of normal, U5 pin 2 will go to a logic LOW condition.
M.2.13
Interlock Status Circuit
The DC Regulator includes only resistors and interconnections
for the circuit. Interlocks are shown on the Overall Schematic,
and Interlock Status logic is located on the LED Board.
Drive signals for contactors K1 and K2, and their auxiliary
contact status return signals pass through the DC Regulator as
part of the overall interlock system. No components are involved.
Three other interlock status circuits pass through the DC Regu-
lator: “Door Interlocks”, “External Interlocks”, and “Interlock
String DC”. Door Interlock status and External Interlock status
are indicated on the ColorStat™ panel, and are also available for
remote readout.
M.2.14
LCD Multimeter
The LCD Multimeter allows for metering of the various supplies
on the DC Regulator. When using an external meter to measure
supplies at the Test Points, the LCD meter switch should be in
the OFF (number 1) position.
DX-25U
M-4
888-2297-002
WARNING: Disconnect primary power prior to servicing.
