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61
3.2
DISMANTLING THE INSTRUMENT
3.2.1
General information
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This section provides the dismantling procedures required for the removal of components during repair and
routine maintenance operations. All circuit boards removed from the oscilloscope should be adequately
protected against damage, and all normal precautions regarding the use of tools must be observed.
During dismantling procedures, a careful note of all leads disconnected must be made so that they may be
reconnected to their correct terminals during assembly.
Always ensure that the mains supply is disconnected before removing any instrument cover plates.
Damage may result if the instrument is switched on when a circuit board has been removed, or if a circuit
board is removed within one minute of switching off the instrument.
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3.2.2
Removing the instrument covers
The instrument is protected by three covers: a front panel protection cover, awrap-around cover with carrying
handle, and a rear panel.
To facilitate removal of the wrap-around cover and the rear panel, first ensure that the front cover is in position.
Then proceed as follows:
— hinge the carrying handle clear of the front cover; to this end, push both pivot centre buttons (Fig. 3.2.).
r.
—stand the instrument on its protective front cover on a flat surface
— slacken the two coin-slot screws located on the rear panel
— lift the rear panel and unplug the connector on the power supply board
— lift off the wrap-around cover
— for access to the front-panel, stand the instrument horizontally and snap off the front cover.
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3.2.3
Removing the carrying handle
—Prise off the centre knobs from each pivot, using a screwdriver (Fig. 3.3) in one of the small slots at the
sides of the knobs
— Remove the cross-slotted screws that are now accessible
—Bend both arms of the handle slightly outwards and take it off the cabinet
— Grip and arms of the carrying handle must be ordered separately (see list of mechanical parts). A complete
carrying handle can easily be constructed by pressing the arms into the grip.
3.2.4
Removing the bezel and the contrast plate
— Take hold of the bezel's bottom corners and gently pull it from the front panel.
— The contrast filter can be removed by pressing it gently out of the bezel.
3.2.5
Removing the knobs and the text plate
— The channel B POSITION, the X POSITION, the DTB LEVEL and the MTB LEVEL knobs can be removed
after prising off the knob caps and unscrewing the slotted nuts that are then accessible.
— The remaining small knobs can be pulled off the shafts.
— The AMPL/DIV and TIME/DIV switch knobs can be removed after prising off the knob caps and unscrewing
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the hexagonal nuts that are then accessible.
— The delay -time multiplier knob (Fig. 3.4) can be removed in the following way:
— Slacken screw A using a hexagonal key and pull the knob from the spindle
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— Remove the nut B and withdraw the ring from the spindle
lNhen fitting the vernier control, turn the spindle of the potentiometer fully anticlockwise. Place the ring on
the spindle so that the reference line corresponds to the zero mark on the calibrated scale. Then lock it with
nut B. Fit the inner knob so that its cam is engaged with the slot in the ring. Rotate the inner knob until its
zero mark coincides with the reference line on the ring. Secure the assembly by tightening screw A.
— When the knobs have been removed, the text plate can be taken off after removing the hexagonal nuts of
the AMPL/DIV and the TIME/DIV switches.
3.2.6
Removing the front assembly
In order to gain access to parts on the AMPL/DIV switches, to replace trimmer capacitors or other components
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on the attenuator board, it is best to remove the front panel assembly as a whole in accordance with the
following procedure:
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