Hameg HM 203, Руководство пользователя

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tains the power fuse, which is interchangeable for the dif­
ferent mains/line voltages. The fuse holder with its
square top plate can be pulled out, and
changing of the
mains/line voltage is possible by turning this plate 90
degrees for each of the four voltages marked on the plate
(see triangle on the rear panel below the fuse holder).
The fuse holder should then be plugged in again in the
desired position, which should be the
closest value of
the measured mains/line voltage in your area The set
value is always readable on the lower edge of the fuse
holder. The power fuse must correspond to the voltage
selected and when necessary should be replaced. The
type and rated current are given on the rear panel and in
the Service Instructions.
Before applying power to the oscilloscope, it is recom­
mended that the following simple procedures are per­
formed:
— Check that all pushbuttons are in the out position, i.e.
released.
— Rotate the three variable controls with arrows, i.e.
TIMEBASE variable control, CH.I and CH.II at­
tenuator variable controls, fully counterclockwise in
their calibrated detent.
— Set the control knobs with marker lines to their mid­
range position (marker lines pointing vertically).
— The slide switch in the X-Section should be set to its
uppermost AC position.
— Both input coupling slide switches for CH. I and CH. II
in the Y-Section should be set to the GD position.
Switch on the oscilloscope by depressing the red
POWER pushbutton. An LED will illuminate to indicate
the working order. The trace, displaying one baseline,
should be visible after a short warm-up period of 10
seconds. Adjust
Y-POS.I and X-POS. controls to center
the baseline. Adjust INTENS, (intensity) and FOCUS
controls for medium brightness and optimum sharpness
of the trace. The oscilloscope is now ready for use.
If only a spot appears (CAUTION! CRT phosphor can be
damaged.), reduce the intensity immediately and check
that the
HOR. EXT. pushbutton is in the released (out)
position. If the trace is not visible, check the correct posi­
tions of all knobs, buttons, and switches (particularly
AT/NORM. button in out position).
To obtain the maximum life from the cathode-ray tube,
the minimum intensity setting necessary for the measure­
ment in hand and the ambient light conditions should be
used
Particular care is required when a single spot is
displayed, as a very high intensity setting may cause
damage to the fluorescent screen of the CRT. Switching
the oscilloscope off and on at short intervals stresses the
cathode of the CRT and should therefore be avoided.
In spite of Mumetal-shielding o f the CRT, effects o f the
earth's magnetic field on the horizontal trace position
cannot be completely avoided. This is dependent upon
the orientation o f the oscilloscope on the place of
work. A centred trace may not align exactly with the
horizontal center line o f the graticule. A few degrees of
misalignment can be corrected by a potentiometer
accessible through an opening on the front panel
marked TR.
DC Balance Adjustment
The vertical preamplifiers for CH.I and CH.II contain in­
put source followers with matched dual FETs. After long
periods of use the FET characteristics may change which
can alter the DC balance of the vertical amplifier.
A quick check can be made on each channel by rotating
the variable control knob on the attenuator switch to and
fro, clockwise and back to the calibrated detent
C. If the
trace moves from the vertical position (up or down) by
more than 1 mm, the DC balance will require readjust­
ment. This check should be made after a 20 minute
warm-up period.
Adjustment procedure
The following instructions should be performed to obtain
the correct DC balance adjustment of both channels.
— Remove all input cables and adjust oscilloscope con­
trols to display the baseline.
— Center the baseline using Y-POS. and X-POS. con­
trols.
— Set attenuator switches to 5mV/cm and input cou­
pling switches to GD.
— Release all pushbuttons in the Y-Section.
— Place the oscilloscope so that it rests firmly on its back
(upright position) and locate DC balance adjustment
potentiometer access holes — marked
CH.I DC-
BALANCE CH.II - which are found underneath the
instrument.
— Insert a screwdriver (blade approx. 3 mm, length min.
20mm) in CH.I hole. Behind the hole, a plastic funnel
with slotted bottom is located.
— Rotate AMPL. I variable control to and fro and adjust
balance pot so that the baseline no longer moves up or
down. When the trace remains steady, correction of
CH.I is completed.
— Depress CHI/II button. Repeat adjustment procedure
for CH.II
Probe Adjustment
To achieve the undistorted display of signals when using
an X I 0 or X I 00 attenuator probe, the probe must be
M3 20 3-4