c. No ColorStat™ panel indicators are illuminated RED.
Check the Over Temp LED DS2 on the Driver En-
coder/Temp Sense Board. If it is RED, the circuitry has
initiated a Temperature Induced Lower command to the
Controller. Possible causes include transmitter tuning or
RF combiner problems resulting in excessive heat sink
temperature on PA Modules RF33 and RF34 or defective
temperature monitoring circuitry. Refer to SECTION S,
Driver Encoder/Temp Sense Board and the transmitter
tuning instructions in the initial turn-on paragraphs in
SECTION II, INSTALLATION.
6.8 Symptom: Unable to raise power
past a certain point. ColorStat™
panel ANT and/or FILTER LED in-
dicate RED.
6.8.1 Possible cause
If the ANT and/or FILTER ColorStat™ panel indicators are
Illuminated RED. The VSWR sensor(s) trip and power reduc-
tion circuitry is activated. There are two possible causes:
a. The phase angle detector(s)on theOutput Monitor are not
nulled yet on a new installation or recent antenna system
work. Refer to SECTION II, Installation/Initial Turn On,
for the phase angle detector null procedure.
b. If detectors are nulled and transmitter has been operating
normally for some time, troubleshoot the cause of VSWR
problems.
6.9 Symptom: Unable to raise power
past a certain point. No ColorStat™
panel indicators Illuminated RED.
6.9.1 Possible cause
6.9.1.1 Analog Input Board maximum power adjustment
R27 misadjusted or defective.
Check associated circuitry and monitor at test points TP3, TP1,
and TP4. Refer to SECTION J, Analog Input Board, for more
detailed information.
6.9.1.2 Analog Input Board, half power step up circuit may
have failed.
Check Q7 and Q8 circuitry. Refer to SECTION J, Analog Input
Board, for more detailed information.
6.9.1.3 PA Turn on/Turn Off control signals on Modulation
Encoder A37 may be incorrect.
If this type of failure is of such magnitude to limit full power
output, severe audio distortion should also be noted. Check for
the correctnumber of steps to be turned on by viewingthe green
LED’s on each of the PA Modules. If LED’s are not illuminated,
i.e. steps 1-48, check to see if the control signal is at the
appropriate Encoder output. Refer to SECTION L, Modulation
Encoders, for additional information.
6.9.1.4 Open fuses on Fuse Boards A24 or A25.
If a fuse has opened, there will be no voltage to a group of eight
amplifiers.
6.10 Symptom: Transmitter turns ON
(Low, Medium, or High Indicators
Illuminate) but will not modulate.
6.10.1 Possible Causes
Because audio is added to a DC voltage relative to the power
output level, any problem that would affect the (Audio + DC)
signal would also affect the power level. The DC is added to the
audio earlyin the analog input circuitry. If the transmitter power
output control functions normally but there is no modulation,
the problem is either before the transmitter or is occurring in the
first few stages of the Analog Input Board.
6.10.1.1 Modulation not reaching transmitter
Verify that audio is reaching the audio input terminals on the
External Interface.
6.10.1.2 Analog Input Board
Only the circuitry associated with Analog Input Board compo-
nentsU6,U9,and U7 wouldaffectmodulationbutnot the power
control. Refer to SECTION J, Analog Input Board, for addi-
tional information.
6.11 ColorStat™ panel Overcurrent
Fault Indication
TheOvercurrentFaultmonitorsthesupplycurrentofthePAPower
Supply and will generate a TYPE 1 Fault any time the PA current
reaches a preset overload level. Both average and peak current are
monitored and combined for the Overcurrent Fault.
6.11.1
Random Faults With Program Audio. Possi-
ble Causes:
a. OVERMODULATION: Random faults with modulation
often indicates that the peak overload current is being
exceeded by overmodulation of the transmitter. Check the
modulation levelwith an oscilloscope if the calibration of
the modulation monitor is in question.
b. LOW FREQUENCY SIGNALS: If the modulation level
is correct, there may be sub-audible signals feeding into
thetransmitter. Take noteof when theoverloadsoccur and
try to relate the overloads to a particular source.Turntable
rumble, especially during start-up, can be of such level to
cause Overcurrent overloads. A switchable high-pass fil-
ter in the program line, some audio processors have
switchable low frequency cut-off filters, will filter out the
DX-25U
6-8 888-2297-002 Rev. R: 11-11-96
WARNING: Disconnect primary power prior to servicing.
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