Protective Membrane/Shield; Ground Check; Ground Loop Isolation; Crooked Or Loose Key Tops - IBM 3277 Troubleshooting Manual

5.4.5 Protective Membrane/Shield
When removing a key module from a keyboard with the
protective shield, care must be taken not to puncture the
shield when snapping out the defective module.
5.4.6 Ground Check
There should be continuity between the two base plate
grounding studs (Diagram
5-13)
and the dc ground circuit
on the PC board. Grounding can be checked with an
ohmmeter connected between the base plate and the
ground pin, 008, at the interface signal connector, KB 1.
5.4.7 Ground Loop Isolation
Nonconductive inserts have been added to the base plate
holding screws on some keyboard assemblies to isolate the
base plate and PC board dc ground from the all-keys
assembly. With the keyboard assembly disconnected from
the 3277, check to ensure that the base plate and all-keys
assembly are not electrically shorted.
5.4.8 Crooked or Loose Key tops
Key module stems can be formed left or right to align a
crooked looking key top. The keystem ears can
be
widened
to tighten loose key tops.
5-22