AT&T System 25 - Manual (Page 308)

APPENDIX C: System Additions or Changes
Replace Circuit Pack
Replace a CP if it fails or becomes damaged.
1.
2.
3.
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5.
6.
Make sure that your hands are clean and dry. Put on a wrist
grounding strap, and clip it to the grounding block at the back of the
cabinet.
With your thumb, pull up on the latch pin.
When the latch is up, pull down on the latch lever until the lever
stops at an angle of about 30 degrees to the floor.
Pull the CP out of the slot, and set it aside.
Insert the replacement of the same type CP in the same slot,
following the instructions above for adding a CP.
Package the defective CP in protective material, and return it per
local instructions.
C-7