d. Use standard practices to repair poor solder connections
with a low-wattage soldering iron.
e. Clean cases and bodies of all capacitors.
f. Inspect bleeder resistors when inspecting electrolytic ca-
pacitors.
5.2.3.3
Fixed Resistors
Preventive maintenance of fixed resistors is accomplished by
performing the following steps:
a. When inspecting a chassis, printed-circuit board, or dis-
crete component assembly, examine resistors for dirt or
signs of overheating. Discolored, cracked, or chipped com-
ponents indicate a possible overload.
b. When replacing a resistor, ensure that the replacement
value agrees with the schematic diagram and parts list.
c. Clean dirty resistors with a small brush.
5.2.3.4
Variable Resistors
Preventive maintenance of variable resistors is accomplished by
performing the following steps:
a. Inspect the variable resistors and tighten all loose mountings,
connections, and control knob set-screws (do not disturb
knob alignment). Sliding taps on adjustable resistors should
be snug, but not excessively tight. Overtightening can damage
the resistor.
b. Clean dirty resistors with a small brush.
c. When dirt is difficult to remove, clean with a lint-free cloth
moistened with an approved cleaning solvent.
5.2.3.5
Fuses
Preventive maintenance is accomplished by performing the fol-
lowing steps:
CAUTION
USE ONLY AN EXACT REPLACEMENT FUSE. FUSES OF THE
SAME SIZE AND/OR RATING FROM A DIFFERENT MANUFAC-
TURER MAY NOT FULFILL THE REQUIREMENT FOR EXACT
REPLACEMENT.
a. When a fuse blows, determine the cause before installing
a replacement.
b. Inspect fuse caps and mounts for charring and corrosion.
c. Remove dirt with a small brush.
d. If necessary, tighten fuse clips and connections to the clips.
Fuse clip tension may be increased by pressing the clip
sides closer together.
5.2.3.6
Switches
Preventive maintenance of switches is accomplished by perform-
ing the following steps:
a. Inspect switch for defective mechanical action or loose-
ness of mounting and connections.
b. Examine cases for chips or cracks. Do not disassemble
switches.
c. Check contacts for pitting, corrosion, or wear.
d. Operate the switches to determine if they move freely and
are positive in action.
e. Be sure to include an inspection of the power supply
discharge switches S9, S10 and S12 located in the inter-
locked RF Amplifier and Driver Compartments.
5.2.3.7
Indicators and Front Panel Switches
Preventive maintenance of indicator lamps and control switches
is accomplished by performing the following steps:
a. To remove an indicator bulb (LOW, MED, HIGH,
RAISE or LOWER) pull out on the indicator button. The
indicator lamp may then be removed. When re-installing
the button, care must be taken to avoid disrupting nor-
mal operation.
b. Replacement of a front panel switch requires removal of
the Switch Board behind the meter panel.
5.2.3.8
Printed Circuit Boards
Preventive maintenance of printed circuit boards is accomplished
by performing the following steps:
a. Inspect the printed circuit boards for cracks or breaks.
b. Inspect the wiring for open circuits or raised foil.
c. Check components for breakage or discoloration due to
overheating.
d. Clean off dust and dirt with a clean, dry lint-free cloth.
e. Use standard practices to repair poor solder connections
with a 40 Watt soldering iron.
5.2.3.9
Air System
a. The air filters should be routinely washed with soap and
water. Intervals between cleaning will depend on the envi-
ronment.
b. Replace filter when it shows signs of deterioration.
5.2.3.9.1
Fan Motor B1 Through B4 Replacement
It is very probable that the fan blade will be locked or “frozen”
to the shaft of the motor after years of operation. Because of this
it will be necessary to remove the fan frame and blower assembly
to service the motor.
WARNING
ENSURE ALL PRIMARY AC VOLTAGE HAS BEEN REMOVED
FROM TRANSMITTER AND A GROUNDING STICK IS USED TO
GROUND ALL POINTS WHERE AC OR RF POWER HAS BEEN
APPLIED BEFORE PROCEEDING WITH THE FOLLOWING PRO-
CEDURE.
a. Remove the rear panels of the Output Network Compart-
ment.
b. Disconnect the three wires from the failed motor to the fuse
block.
c. Remove the inner fan cage panel which will allow any of
the four fans to be pulled straight back.
d. Remove the 4 screws fastening the fan frame to the cabinet
and remove the fan assembly.
Strap the replacement motor in the High Voltage configuration
(460 VAC) shown in Figure 5-1. Wire the motor as shown on the
Overall Schematic, 839-7855-151, to ensure the motor will rotate
in the same direction as the other three.
DX-25U
5-2
888-2297-002
Rev. Z1: 06-02-00 Additional info to ECN 46105
WARNING: Disconnect primary power prior to servicing.
