alert transistor and J7-11 input will go LOW. A Type 4 Fault will
be generated by comparator U67-1.
Q.5.5.4
Analog to Digital Converter: +15V Supply
The Analog to Digital Con15 VDC supply “Fault Alert”
output enters the LED Board at J9-9. If the “Fault Alert” goes
LOW, a Type 4 Fault will be generated by comparator U67-2.
Q.5.5.5
Analog to Digital Converter: +5V Supply
The Analog to Digital Con5 VDC supply “Fault Alert”
output enters the LED Board at J9-3. If the “Fault Alert” goes
LOW, a Type 4 Fault will be generated by comparator U67-13.
Q.5.5.5.1
Analog Input Board: -15V Supply
The Analog Input Board -15 VDC supply “Fault Alert” output
enters the LED Board at J7-13. If the “Fault Alert” input goes
LOW, a Type 4 Fault will be generated by comparator U68-1.
Q.5.5.5.2
Analog to Digital Converter: -15V Supply
The Analog to Digital Converter -15 VDC supply “Fault Alert”
output enters the LED Board at J9-7. If the “Fault Alert” goes
LOW, a Type 4 Fault will be generated by comparator U68-2.
Q.5.5.5.3
Type 4 Faults, Status Indicator Circuits
When a comparator’s output is LOW (no fault), an invertor
provides a logic HIGH signal to illuminate the GREEN section
of the LED, and two invertors in series provide a logic LOW
(“no fault”) signal to the External Interface. When a compara-
tor’s output is HIGH (“FAULT”), a logic driver output goes
HIGH and illuminates the RED section of the LED and the two
invertors in series provide a logic HIGH (“FAULT”) signal to
the External Interface.
Q.5.6
Type 5 Faults Circuit
There is only one Type 5 Fault, a “Conversion Error.” A Con-
version Error fault clears all digital audio data latches in the
Modulator section, which turns all PA modules OFF. The only
Conversion Error circuit located on the LED Board is the status
indicator. All other Conversion Error fault circuits are located
on the Analog to Digital Converter. Refer to SECTION K,
Analog to Digital Converter, for a description of Conversion
Error detection and logic circuits.
The Conversion Error status indicator circuit is shown on sheet
5 of the LED Board schematic diagram. The circuit includes
AND gate U25-3, Buffer/Driver U56-15, and Invertor/Drivers
U41-6/8/10.
Gate U25-3 inhibits “Conversion Error” fault indications unless
the transmitter is ON and the PA OFF signal from the turn-
on/turn-off logic has been released. An “OVERDRIVE IN-
HIBIT-L” signal from the turn-on/turn-off logic on the
Controller inhibits red “Conversion Error Fault” indications
when the transmitter is OFF, when the PA is held OFF during
the step-start sequence, or when a Fault input to the turn-
on/turn-off logic turns the PA “OFF.”
There are two inputs to AND gate U25:
a. The “OVERDRIVE INHIBIT-L” at pin 2
b. A “Conversion Error” logic signal, from the Conversion
Error circuit on the Analog to Digital Converter, at U25
pin 1.
When the “OVERDRIVE INHIBIT-L” signal is present, the
output of the gate will be LOW no matter what the “Conversion
Error” logic signal state is and the Conversion Error indicator
will be green.
When the “OVERDRIVE INHIBIT-L” signal is released, U25
pin 2 goes HIGH and the output of the gate depends on the
Conversion Error logic signal. When a “Conversion Error-H”
signal is present, U25-3 goes HIGH.
EXTERNAL INDICATE: When U25-3 is HIGH (“Conversion
Error Fault”), invertor U41-10 output goes LOW and invertor
U41-8 output goes HIGH, providing a Fault-H output to the
External Interface.
Q.5.7
Type 6 Fault Circuit
The Blown Fuse indicator circuit is shown at the bottom of Sheet
4 of the LED Board schematic, 839-7855-184, in the Drawing
Package.
A logic HIGH from Blown Fuse Indicator circuits on the Modu-
lation Encoders will bring J2-5 input HIGH and illuminate DS4
on the ColorStat™ panel RED. The transmitter will operate
normally, and a power reduction may be noticed, depending on
which RF amplifier has failed.
Q.5.8
“RF Sense” Circuits on the LED Board
“RF SENSE” circuits provide GREEN indications for the Os-
cillator, Buffer, and Predriver status indicators on the Color-
Stat™ panel when RF output is present. If any section fails (has
no RF output), only the FIRST section where RF fails will
indicate RED, even though the following sections also have no
RF output. Example: If the Oscillator fails, the Buffer and
Predriver status indications will remain GREEN even though
they also have no RF output.
Because RF failure causes an UNDERDRIVE fault, the RF
sense circuits provide only indications to identify the section in
which the fault occurred. Figure Q-8 is a simplified diagram of
“RF Sense Circuits.”
RF sense circuits are shown on sheet 5 of the LED Board
schematic diagram. RF sense circuits include diode detectors in
the RF section, comparators on the LED Board, and invertors
and logic gates to inhibit “fault” indications for following “RF
Status” indicators.
Q.5.8.1
“Oscillator Fault” Sensing
With normal output, the Oscillator output is a square wave,
switching between zero to +5 VDC. The comparator (U5-14)
inverting input is the output of a peak detector and is normally
at approxi5 VDC. The non-inverting input will be
approximately 1 Volt or less. The inverting input is more positive
than the non-inverting input and the TTL level logic output will
be LOW.
If the Oscillator has no RF output, the input to the diodes on the
Oscillator will be a positive DC voltage. The comparator’s
inverting (-) input is pulled toward ground by a resistor and will
be LESS positive than the Oscillator DC output. The compara-
tor’s non-inverting (+) input is pulled to +5 VDC and will be
DX-25U
Q-18
888-2297-002
Rev. R: 11-11-96
WARNING: Disconnect primary power prior to servicing.
