Harris DX 25U, Техническое руководство

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WARNING
ENSURE ALL POWER IS REMOVED FROM TRANSMITTER AND
THAT THE GROUNDING STICK HAS BEEN USED TO DIS-
CHARGE ANY RESIDUAL VOLTAGE WHERE POWER HAS
BEEN APPLIED BEFORE THE TAPS ON THE HIGH VOLTAGE
AND/OR LOW VOLTAGE TRANSFORMERS ARE CHANGED.
For example if the supply voltage reading is too high, remove
all AC power to the transmitter and retap the PA Power Supply
transformer T1 to the next highest primary number. If the
transformer is presently tapped to 430/0, change the tapping to
430/+4% to reduce the supply voltage.
6.13
ColorStat™ panel Supply Fault
The PA Power Supply Fault circuit will not allow the transmitter
to operate if an imbalance exists in the 3-phase AC input. This
will cause excessive heating of the PA Power Supply trans-
former. If the overload occurs only intermittently, the power
supply balance is marginal and is probably faulting on low
frequency modulation peaks. If the fault occurs consistently,
even without modulation, the problem is more serious and
should be attended to immediately.
6.13.1
Possible Causes
6.13.1.1
Input AC 3 Phase Line Imbalance
Measure the 3 phase line voltages. They should be within 5%
of each other. If the line voltages are not in balance, the utility
company should be contacted to rectify the problem. Note that
line imbalance not only affects the transformer heating, but will
also degrade the transmitter AM signal-to-noise performance.
WARNING
ENSURE ALL POWER IS REMOVED FROM THE TRANSMITTER
AND THAT THE GROUNDING STICK HAS BEEN USED TO DIS-
CHARGE ANY RESIDUAL VOLTAGE WHERE POWER HAS
BEEN APPLIED BEFORE PERFORMING THE FOLLOWING
STEPS.
6.13.1.2 Open +115 VDC Supply Rectifier Fuse
Remove the rear panel of the Driver Compartment and check
F13, F14, and F15. If an open fuse is detected, check the
asso115 VDC supply rectifier.
6.13.1.3
Failed PA Power Supply Transformer T1
If the rectifiers check good and the AC line voltage balance is
within specifications, the PA Power Supply transformer may
have failed windings in one of the sections. It is sometimes
possible to compare resistance readings for each primary wind-
ing to locate a failed winding
6.13.1.4
Low Frequency, High Level Modulation
The sensing circuit for the Supply overload fault detects the
amount of full wave power supply ripple on the +115 VDC
supply. This 100Hz/120Hz component will be the greatest when
the transmitter is modulated at this audio frequency range. High
modulation levels with frequencies from 90-140Hz could be
sensed as a fault. This condition should normally not occur if
the three phase line voltages are well balanced. If the balance is
marginal, then Supply fault overloads could occur.
6.13.1.5 Overload Settings
Refer to SECTION V, Maintenance, for the Power Supply
Protection overload adjustment procedure.
CAUTION
DO NOT MAKE ANY ADJUSTMENTS TO THE POWER SUPPLY
PROTECTION OVERLOAD SETTINGS UNTIL ALL OF THE PRE-
CEDING CHECKS LISTED ABOVE HAVE BEEN PERFORMED.
TRANSMITTER DAMAGE COULD OCCUR IF THE OVERLOADS
ARE IMPROPERLY SET.
6.14
ColorStat™ panel Underdrive Fault
NOTE
The transmitter may indicate an UNDERDRIVE overload if a
direct short exists in the PA Power Supply. This could be caused
by shorted MOSFET transistors in the PA Supply Discharge cir-
cuit (crowbar) or a defective shorting switch. The overload indi-
cated could be an UNDERDRIVE fault if the Driver Supplies do
not reach their proper voltage. An Underdrive condition could
be sensed before an OVERCURRENT overload is detected.
WARNING
ENSURE ALL POWER IS REMOVED FROM THE TRANSMITTER
AND THAT THE GROUNDING STICK HAS BEEN USED TO DIS-
CHARGE ANY RESIDUAL VOLTAGE WHERE POWER HAS
BEEN APPLIED BEFORE PERFORMING THE FOLLOWING
STEPS.
6.14.1
Possible Causes
6.14.1.1 High Voltage Supply Short
Remove AC power to the transmitter and remove the Driver
Compartment and RF Amp Compartment rear access panels.
Isolate the PA Power Supply from the RF amplifiers by
removing F1 through F9 on Fuse Board A24, F1 through F8
on A25, and F20 located on T1. Measure the resistance to
ground of the PA Power 230 VDC bus bar on the
Fuse Boards. The resistance should be approximately 500
Ohms. If it is not, troubleshoot the PA Power Supply Dis-
charge Circuit (crowbar). Refer to the DX-25U Overall Sche-
matic, 839-7855-151, in the Drawing Package for circuit
details.
6.14.1.2 Failed Driver Supply (+115 VDC)
Note the PA VDC reading on the front panel multime-
ter while pressing the LOW button. If the voltage deflects
upward, but the VDC indication on the RF MUL-
TIMETER does not, there is a problem in the driver supply
voltage circuit. Check F10 on the Fuse Board A24. Also check
F13, F14, F15, and C7, C8, C9. Refer to the DX-25U Overall
Schematic in the Drawing Package for circuit details.
6.14.1.3
Failed Predriver Supply (+60 VDC)
Observe the voltage rise in the PREVDC position
on the RF MULTIMETER. It should reach approximately 50
Volts within 1 second. If it does not deflect upscale, check F21,
DX-25U
6-10 888-2297-002 Rev. R: 11-11-96
WARNING: Disconnect primary power prior to servicing.