IBM 3279 2A Maintenance Information page 57

3279 MIM
II. Observing normal CRT safety precautions (see
"CRT Safety" at the front of this manual),
move the CRT from the display unit and put it
face down on the bezel.
12. Remove the wrap tie that secures the degauss
coil.
13. Remove the degauss coil, ground braid and
securing clips from the CRT.
14. Prepare a surface for the CRT and move the
CRT to that surface.
4.8.3.2 Replacement
I.
Ensure that the case that contains the new CRT
is the correct way up.
2. Remove the new CRT from its case and set it
on the bezel with the EHT connector to the
front.
3. If you do not have a new piece of plastic foam
(acoustic shield) to fit around the deflection
coils, transfer the plastic foam from the old
CRT.
4. Pack the old CRT in the case provided with the
neW CRT.
5. Install the degauss coil, ground braid and
securing clips on the new CRT. Keep the
ground braid between the tube and the degauss
coil.
6. Secure the degauss coil in position with the
wrap.
7. Observing normal CRT safety precautions,
install the CRT in the display unit, taking care
to avoid trapping or fouling any cables.
8. Insert the washers and nuts but do not tighten
the nuts.
9. Check that all cables and connectors within the
display unit are free and accessible,
10. Connect the degauss coil (P27).
11. Center the CRT in the display and tighten the
nuts.
12. Check that the CRT is centered by replacing
the bezel and repeat Step ,11 as necessary.
13. Remove the pin protector from the CRT and
insert
it
on the failed CRT.
Chapler 4. Removal and Replacement Procedures 4-8
14. Slide the convergence coil assembly onto the
CRT neck and position the assembly over the
interelectrode gap
as
shown in Figure 4-8.
Adjust the angular alignment to the stated
tolerance. Use the machine base as a reference.
Note: If the angular alignment is incorrect, the
convergence pattem will
be distorted.
15. Secure the convergence coil assembly by the
clamp but do not over-tighten the screw.
Note: If the coil assembly is too far forward
there will be too little sensitivity, if it
is
too far
to the rear. there will be too much sensitivity.
16. Check that the jumper on the analog card
matches the CRT type (see Figure 4-7).
17. Reconnect the ground braid clamp (see Figure
6-9) and replace the jumper link,
18. Install:
The EHT bleed assembly (see section
4.8.4.2. steps 2 through 4)
The amplifier card (see section 4.8.1)
The video card (see section 4.8.2)
• The analog card (see section 4.5.4)
• The power supply (see section 4.5.2)
19. Reconnect ail plugs that were disconnected
during the removal procedure.
20. Ensure that all ground connections are
reconnected securely. including the two on the
analog card heatsink.
21. Check that all cards and connectors are
correctly seated.
22. Replace the rubber clamp on the internal
power cable near the ON/OFF switch.
23. Secure the bezel to the front of the display
unit (see section 4.4).
24. Carry out Display Setup as detailed in
Chapter 5.
25, On completion of the initial checks and the
setting up procedures, replace all the safety
covers and close the logic gate.