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