Dell 2135cn Service Manual page 751

Chapter 3 Removal and Replacement Procedures (RRPs)
4) Slide the COVER ASSY ESS frontward
obliquely, and then close the COVER
ASSY ESS until it locks into place.
5) Shift the COVER ASSY ESS to front
side, secure the SCREW KNURLING.
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Version 
2008.03.31