Section Q
LED Board (A32)
Q.1
Introduction
This section describes the LED Board, and includes circuit
functions and descriptions.
The LED Board includes fault and overload detection circuits,
logic and status indicator latches, and drivers for both front-panel
and remote status indicators. The transmitter ColorStat™ panel
indicators are mounted on the LED Board.
Q.2
Location
The LED Board is located on the back of the Center Control
Compartment door. The ColorStat™ panel LED indicators are
mounted on the back of the LED Board.
Q.3
Transmitter Fault Types
The fault and overload circuits in the transmitter can be grouped
into “FAULT TYPES,” depending on the action taken when a
fault is detected. The following paragraphs describe each fault
type, the corrective action taken when the fault occurs, and fault
indications. Refer to table Q-1 for a list of faults and overloads
by fault type.
Q.3.1
Type 1 Fault: Turns Transmitter Off
Type 1 faults generate an “OFF” command and remove the +230
VDC by de-energizing the PA Power Supply contactors. The trans-
mitter must be manually turned back “ON” after the fault is cleared.
The appropriate ColorStat™ panel LED will latch RED.
Q.3.2
Type 2 Fault: Recycles Transmitter Off/On
One Time
Type 2 Faults may be temporary. To determine if they can be
cleared, Type 2 Faults de-energize the PA Power Supply contac-
tors for approximately one second, then turn the transmitter back
“ON” by starting a normal step-start cycle. Type 2 Faults also
cause the transmitter ColorStat™ panel indicator to latch red.
Q.3.2.1
Repeated Type 2 Faults Become Type 1 Faults
If the same fault is detected as soon as the transmitter is cycled
back ON, it becomes a Type 1 Fault and turns the transmitter
“OFF.”
Q.3.3
Type 3 Fault: Lowers Transmitter Power
A Type 3 Fault will reduce transmitter power until the fault
condition is within limits.
Type 3 Faults occur when repeated VSWR “hits” occur in a short
period of time, indicating high reflected power, or if the PA module
temperature reaches dangerous levels. The temperature monitor
circuit on the Driver Encoder/Temp Sense Board will begin a
“Temperature Induced Lower” command to reduce power until the
temperature level is within limits. For a VSWR lower condition, the
appropriate indicator on the ColorStat™ panel will latch RED.
For Temperature Induced Lower” condition, the OVER TEMP
LED on the Driver Encoder/Temp Sense Board will latch RED
to indicate power reduction has occurred.
A single VSWR trip does not lower transmitter power, but
generates a Type 4 fault and turns the PA OFF for 14 to 19
milliseconds. If the VSWR fault is caused by an arc, lightning,
static discharge, or other transient condition, the cause of the
VSWR fault will clear. Single VSWR trips cause a 0.5 second
RED indication on the ColorStat™ panel or a 0.5 second remote
“VSWR” indication.
A REMOTE “Type 3 Fault” indication is also available to signal
the operator that transmitter power has been lowered.
Q.3.4
Type 4 Fault: Applies PA Turnoff
A Type 4 Fault will turn the RF OFF, zero output power, but the
PA Power Supply will remain energized. This fault sends a “PA
Off” logic signal to the Modulation Encoder and Analog Input
Board to clear all power control data and turn all RF Power
Amplifier modules OFF. A Type 4 Fault causes a RED indication
on the ColorStat™ panel until the fault is corrected.
Q.3.5
Type 5 Fault: Clears Modulator Data
A Conversion Error from the Analog to Digital Converter will
clear all Digital Data to the Modulation Encoders and result in a
PA OFF condition, similar to a Type 4 Fault. The “Conversion
Error” LED on the ColorStat™ panel will turn RED.
Q.3.6
Type 6 Fault: PA Module Blown Fuse Indication
A Blown Fuse indication is caused by any PA Module with a blown
fuse. The indication is present only when the PA Power Supply is
energized. The indication is not latched and resets when the module
is repaired or substituted by FlexPatch™ procedure.
Q.4
Block Diagram Description
The Block Diagram description of the LED Board refers to
Figure Q-1, “LED Board Block Diagram.”
The LED Board contains Fault and Overload circuits, which can
be divided into blocks or sections by “Fault Type.” For most
faults, there are FAULT DETECTION or FAULT SENSING
circuits, LOGIC circuits, STATUS INDICATOR circuits and an
EXTERNAL STATUS output.
Type 1, Type 2, Type 3, and Type 4 faults cause ACTION in other
sections of the transmitter. For each of these Fault Types there is
an OR function and one or more signal outputs to other parts of
the transmitter. Other faults provide only FAULT INDICA-
TIONS on the ColorStat™ panel.
Fault and Overload circuits are reliable and generally trouble-
free. Therefore, maintenance staff will have few opportunities to
become familiar with circuit operation by troubleshooting. If
Rev. R: 11-11-96
888-2297-002
Q-1
WARNING: Disconnect primary power prior to servicing.
