Agilent Technologies 8453 Operator's Manual page 233

Maintenance and Repair
Exchanging the Fan Assembly
4 Replace the plastic and sheet metal rear cover. Push the plastic rear cover
down so that it locates on both sides, see "Removing and Replacing Covers"
on page 109.
5 Reconnect line power and turn on the instrument. Check that the
spectrophotometer passes its self-test, this means that the green light on the
front panel comes on and that you can do a blank measurement from your
software.
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