IBM 3277 Troubleshooting Manual page 77

7. Raise the edge of the all-keys assembly nearest the
key module to be replaced about 1/4 inch. Press
down on the shoulder of the key module until it
snaps out of the retaining plate (Diagram 5-11).
8. Select either removal method, a or b, below, that
is most conven ient.
a. Lift the all-keys assembly, leaving behind the
defective key module. Place the all-keys
assembly rightside up in the clean area.
b. Lift the all-keys assembly, leaving behind the
defective module. Place the all-keys assembly
upside down, either on the existing system
keyboard mounting hardware and brackets or
on prepared supports (such as blocks of wood
or standoffs).
B.
Module Replacement:
1. Observe orientation of the new key module.
Ensure that the alignment lug and keystem are
in the same position as the rest of the modules
in the all-keys assembly.
2. Install new module (PN 1772948) by lowering
the all-keys assembly over the new module (if
step Sa was used for removal) or by snapping
the key module in the retaining plate by hand
from the bottom (if step 8b was used for
removal).
3. Clean the printed circuit board (Diagram 5-12)
and key module flyplates by carefully wiping
each with a lint-free cloth dampened with
isopropyl alcohol. 8e careful not to dislodge or
remove flyplates from key modules.
4. Align the holding screw holes through base
plate, PC board, insulator, and top insulator (if
present). Diagram 7-18 shows the correct
locations of these components. Lower the
all-keys assembly into place.
5. Carefully slide one corner of the keyboard
assembly off the work area edge, and install
one holding screw finger tight. Rotate key-
board assembly carefully, and install remaining
screws finger tight.
6. Turn keyboard assembly upside down, and
tighten all holding screws with a screwdriver.
7. Turn keyboard assembly rightside up, and
reinstall keybuttons in proper locations.
8. Manually check operation of each key module.
9. With an ohmmeter, check for continuity
between the base plate and KB 1 connector
pin 008. The two base plate grounding studs
(Diagram 5-13) must contact the PC board
ground circuit.
10. Install the keyboard assembly on the bottom
pa n, replace keyboard top cover, and
reconnect keyboard to the display station.
Diagram 5-11. Module Removal (Type B)
Diagram 5-12. Circuit Board and Electronics Assembly (Type B)
Ground Stud (2)
Diagram 5-13. Base Plate G rou nd Studs (Type B)
Checks, Adjustments, and Removals 5-19