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4.1 Maintenance of Electron Optical Column
4 - 10
(11) Securely insert the advancing mechanism for the objective lens movable aperture. Fasten
the W-point screw with a hexagon wrench to secure the advancing mechanism.
Fig. 4.1-22 Installing the Objective Lens Movable Aperture
(12) Press either the EVAC switch on the Evacuation Control Panel or the EVAC control button
on the Observation Screen Control Panel; wait until the evacuation process finishes.
EVAC Panel Control Panel
Fig. 4.1-23 Evacuation Control Panel
4.1.3 Maintenance for the Orifice Unit
The orifice unit in the S-3400N rarely becomes dirty due to the presence of an objective lens
movable aperture in the upper part of the column and because the space between them is
evacuated. The orifice unit, however, requires maintenance services in the following cases:
• Image stigma is substantial with a declining resolution. Although the objective lens
movable aperture was serviced according to Section 4.1.2, the stigma could not be
removed and the problem has not been resolved.
• Stigma was still significant when the objective lens movable aperture position was set to
"0" during the observation.
• Some dust fell into the orifice unit.
• It has been more than one year since last servicing under normal usage conditions.
NOTICE: Procedure for servicing the orifice unit are given below. However, this operation,
which involves the handling of tiny components, should be delegated to service
personnel.