Harris DX 25U, Техническое руководство

Страница: 20 / 274

WARNING
TURN OFF SINGLE PHASE AND THREE PHASE PRIMARY
POWER AT THE MAIN DISCONNECT BEFORE REMOVING ANY
REAR PANEL.
a. Remove the rear access panels from the RF Amp Compart-
ment and locate the two Fuse Boards (A24/A25).
b. Remove F20 located on High Voltage Transformer T1
terminal deck; F21 and all other fuses on T1 remain.
c. Remove F1 through F8 on the A25 Fuse Board. This will
minimize inrush current in case of a problem in the step
start sequence or control.
NOTE
Before replacing the rear access panels, make sure nothing is
shorting out the supply. With an ohmmeter, measure the resis-
tance of the +230 VDC supply between the heavy copper buss
bar on the fuse boards and ground. With the positive lead on the
supply, the resistance should be approximately 500 Ohms +/-
10%, which is the resistance of the PA Discharge circuit. Re-
member that S9, S10, and S12 short out the supply when any of
the interlocked RF Amp Compartments behind the front doors
are open.
d. Replace the rear access panels and apply SINGLE phase
AC power to the transmitter at the main disconnect. DO
NOT APPLY THREE PHASE POWER AT THIS TIME.
e. Turn the Low Voltage Power Supply circuit breakers CB1
and CB2 in the Center Control Compartment to the ON
position.
f. All transmitter front panel ColorStat™ panel indicators
should be either red or green (except for the Remote LED,
which will not be illuminated when in the LOCAL posi-
tion). Indicators are bi-color LED’s (except for Local and
Remote indicators, which are single color LED’s).
g. Switch the front panel MULTIMETER to the -8 VDC, +8
VDC, -22 VDC, and +22 VDC positions and check the
readings against the Factory Test Data. These readings
should be within 10% of the Factory Test Data readings.
The readings will be slightly lower when the +230 VDC
PA Power Supply is energized.
NOTE
If the readings are not within 10% of the Factory Test readings,
turn off CB1 and CB2, remove primary AC power at the main
disconnect and review the connections to Low Voltage Trans-
former T2.
2.15.2
Underdrive Overload Test
The following test simulates an Underdrive fault condition by
bringing the transmitter up with 3 phase primary AC OFF. The
importance of this test is to assure that the RF drive sensing
circuitry is functional. Proper drive level is critical to prevent
failures in any of the RF amplifiers, RF1 through RF64, in the
Power Amplifier stage. There are other fault conditions that will
be detected by the Underdrive Overload circuit that are not RF
related failures: i.e. a short across the PA Power Supply during
the step start sequence. Refer to Section IV, Overall System
Theory, and Section VI, Troubleshooting, for a more detailed
understanding of Underdrive overload.
a. Single phase AC power ON, three phase AC power OFF.
b. Depress the LOW power button. Observe the following:
1. K1 step start contactor should energize, quickly drop
out, energize, then drop out a second time.
2. The Underdrive LED on the ColorStat™ panel should
change to AMBER on the first drop out, RED on the
second drop out and remain RED until the display is
reset.
3. K2 in the Step Start Panel should not energize.
4. These events should all occur within two seconds.
2.15.3
PA Power Supply Check
This test will be the first application of three phase AC power to
T1 and will energize the +230 VDC, +115 VDC, and +60 VDC
supplies. It will also determine that the step start sequence is
operating properly.
a. Single phase AC power ON, three phase AC power ON.
b. Place the PA OFF switch, S2, located on the Controller, in
the OFF (up) position.
c. Rotate the front panel Multimeter switch to the PA SUP-
PLY +VDC position.
d. Depress the LOW power button and observe one of the
following:
1. Step start sequence completes, PA supply voltage
comes up to +255 VDC +/-5%.
or
2. Step start sequence drops out due to an Underdrive
fault. or
3. Step start sequence drops out due to an Overdrive
and/or Overvoltage fault.
e. If step d1. was observed, proceed to the Fan Rotation check
f. If step d2. was observed, temporarily disable the Under-
drive overload by placing a clip lead on the LED Board
between TP8 and GND (ground), and then repeat the test.
g. If step d3. was observed, retap T1 to lower the supply
voltage and then repeat the test.
h. Depress the OFF button and observe the PA SUPPLY
+VDC on the Multimeter. The voltage should drop to zero
very quickly. If the voltage bleeds off slowly, troubleshoot
the PA Supply Discharge Circuit (Crowbar). Refer to Sheet
1 of the DX-25U Overall Schematic, 839-7855-151, in the
Drawing Package for details of the PA Supply Discharge
circuit.
i. Repeat the procedure to verify the step start sequence is
functioning properly. The sound of K1 and K2 is propor-
tional to their size.
2.15.4
Fan Rotation Check
The fan motors are three phase and correct rotation must be
verified. If necessary, two of three AC input wires must be
interchanged at 2TB1 in the Output Network Cabinet. Use the
following procedure:
DX-25U
2-8 888-2297-002 Rev. AA: 8/9/2000
WARNING: Disconnect primary power prior to servicing.