N.3.7.1
“PA TURN OFF”
The “PA TURN OFF” control input turns off all PA Modules
through the modulation section of the transmitter. It does NOT
turn off the +230 VDC PA Power Supply.
The “PA TURN OFF” control is intended to turn the RF carrier
OFF during antenna pattern changes, antenna selection, or other
times when transmitter RF output is switched. The “PA TURN
OFF” control is not intended to be used for failsafe or for
transmitter shut down.
As soon as the “PA TURN OFF” control input voltage is re-
moved, the transmitter RF output will return to the power level
determined by the HIGH, MEDIUM, and LOW switches and the
raise/lower controls.
N.3.7.2
“OFF CONTROL”
The “Off Control” control input operates in the same way as the
transmitter front panel “OFF” switch, by de-energizing the PA
Power Supply primary contactor and resetting turn-on/turn-off
control circuits.
The “OFF CONTROL” should be used any time the transmitter
is to be turned OFF for any reason other than a brief interruption
of RF output power during antenna switching or antenna pattern
change operations.
N.3.8
External Interface Power Supplies
N.3.8.1
DC Voltage Supplies to the Board
Four unregulated DC voltages are brought from low voltage
supply Power Distribution Board A39 to the External Interface.
The +8 VDC and -8 VDC supplies are used only for external
monitoring outputs. The +22 VDC and -22 VDC supplies are
used for external monitoring outputs and are regulated to +15
VDC and -15 VDC for circuits on the External Interface and to
supply voltages required for external interfacing.
N.3.8.2
Zener Diode Reg15 VDC and -15 VDC Sup-
plies
Zener-diode reg15 VDC and -15 VDC supplies provide
operating voltages for operational amplifiers U4, U5, U6 and U7.
N.3.8.3
Three-terminal Regulators
Three-terminal IC voltage regulators p15 VDC at up to
175 mA, and -15 VDC at up to 175 mA, for external use. These
voltages are brought out at TB1-11 and 12 (TB1-10, 13 and 14
are ground connections), and can be used as voltage sources for
control input circuits and for status output circuits.
These three-terminal IC voltage regulators are over-current pro-
tected, and their output voltages will decrease if excessive current
is drawn. If these supplies are used for Status outputs, total
current drain cannot exceed 175 mA from either supply.
N.4
Troubleshooting
N.4.1
Symptom: No Remote Control Inputs Operate
N.4.1.1
Possible Cause: Supply voltage for External Inputs
Missing
If the +15 VDC from TB1-11 or the -15 VDC from TB1-12 is
used, check for presence of this voltage. If the voltage is missing,
check voltage regulator U6 for +15 VDC at its output and U9 for
-15 VDC at its output. If there is no output, check the +22 VDC
or -22 VDC input. If a customer-supplied battery or power supply
is used, check its output voltage.
N.4.2
Symptom: Some Remote Control Inputs Do
Not Operate
N.4.2.1
Possible Cause: Faulty Opto-Isolator, Faulty Trans-
mitter Logic, or Faulty Remote Control Equipment
Monitor the dc voltage between the control input terminals on
TB1 or TB2 and activate the remote control equipment. If the
correct voltage appears between the terminals, the problem is in
the transmitter. If the voltage is incorrect, the problem is a shorted
opto-isolator input or the problem is outside the transmitter. To
determine whether the opto-isolator or transmitter logic is at
fault, monitor the voltage across the opto-isolator output termi-
nals while activating the remote control input again.
If the voltage across the opto-isolator output terminals drops to
less than 0.5 Volts, the opto-isolator is operating properly. Refer
to SECTION P, Controller, for information on troubleshooting
the Controller.
N.4.3
Symptom: Remote Status Outputs Do Not Op-
erate
N.4.3.1
Possible Cause: No Supply Voltage For Status Circuits
A positive voltage through circuits external to the transmitter
must be supplied to each status output used, at the proper terminal
on TB1 or TB2. For each remote Status output there should be
a positive voltage on the corresponding terminal on TB1 or TB2.
Determine where the supply voltage for external status circuits
comes from, then check that supply.
N.4.4
Symptom: Some Status Outputs Operate, But
One Or More Does Not (fault Indication On
Transmitter ColorStat™ panel But No Re-
mote Status Indication)
N.4.4.1
Possible Cause: Problem In Transmitter Fault And
Overload Logic
Use a voltmeter or logic probe to check the logic level (input
voltage) to the status interface circuit on the External Interface.
When a fault is present, the input at J6 should be logic HIGH and
the transistor base should be about +0.6 to +0.7 VDC. If the input
is not logic HIGH, the problem is in transmitter fault and over-
load logic. Most fault and overload logic is described in SEC-
TION P, Controller and SECTION Q, LED Board.
N.4.4.2
Possible Cause: Problem is Outside the Transmitter
Check for voltage at the corresponding terminal on TB1 or TB2.
When there is a “STATUS” indication (red LED or illuminated
DX-25U
N-4
888-2297-002
12-12-94
WARNING: Disconnect primary power prior to servicing.
