Fig. 4-7. Honeycomb assembly and wire color code to the pin
connector.
3. Turn the Type 491 on its side (see Fig. 4-11). Remove
the nylon rocker arm from the DISPERSION RANGE switch
SW365.
4. Unlock the IF control assembly and swing the circuit
board assembly up to its fully extended position. Now
gently remove the honeycomb assembly by slipping the
assembly towards the rear to free the mounting screw head
and pulling the assembly out and to the rear.
5. Turn the honeycomb assembly over and place it upside
down on a block or box as shown in Fig. 4-11. CAUTION-
Do not bend or damage the pin connectors.
6. Remove the screws that fasten the bottom plate to
the assembly and remove the bottom plate.
7. If power is to be applied, make certain all connections
are correct to the square pin connector and the connectors
are free of short circuit conditions. The DISPERSION RANGE
switch must be manually switched on the honeycomb assem-
bly when changing DISPERSION RANGE positions. Fig.
4-11 shows the circuit sections in each cell of the honey-
comb assembly.
Cathode-Ray Tube Replacement
Protective clothing and safety glasses should be worn when
handling the CRT. Avoid striking the tube on any object which
might cause the tube to crack or implode. The CRT may be
stored by placing the tube face down on a smooth surface
with a protective cover or soft mat under the faceplace to
prevent scratches.
The removal and replacement procedure for the CRT tube
and shield assembly is as follows:
1. Unsolder the trace rotation leads.
4-8
Fig. 4-8. Connector assembly board for the RF oscillator assembly
and wiring color code to the pin connector.
2. Disconnect the deflection plate pin connectors, Pull
out on the connectors so the pins will not be bent.
3. Remove the CRT base socket,
4. Remove the two (2) nuts and graticule light holders
which secure the front of the CRT shield to the subpanel.
Remove the graticule lights from the studs and position them
out of the way.
5. Remove the two phillips-head screws that hold the two
right angle mounting brackets at the base of the CRT shield.
See Fig. 4-12.
6. Slide the CRT assembly to the rear of the instrument
until the faceplate clears the mounting studs; twist the
assembly clockwise to clear the right angle brackets, then
lift the assembly up and out of the instrument.
7. Loosen the slot screw at the base of the CRT clamp
inside the CRT shield.
8. Place the left hand on the CRT faceplate and push
forward on the tube base with the right hand to slip it out
of the base clamp. As the CRT starts out of the shield, grasp
it firmly with the left hand. When the tube is free of the
clamp, slide the shield completely off the CRT.
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