24
Subject to change without notice
T 2
made up locally. It is important that this attenuator is
shielded. For local manufacture, the electrical compo-
nents required are a 1M
Ω
±1% resistor and, in parallel
with it, a trimmer 3-15pF in parallel with approx. 12pF.
One side of this parallel circuit is connected directly to
the input connector of CH.I or CH.II and the other side
is connected to the generator, if possible via a low-
capacitance coaxial cable. The series attenuator must
be matched to the input impedance of the oscilloscope
in the
5mV/div.
position (variable control to
CAL.
,
DC
input coupling; square tops exactly horizontal; no ramp-
off is permitted). This is achieved by adjusting the
trimmer located in the 2:1 attenuator.
The shape of
the square-wave should then be the same in each
input attenuator position.
Operating Modes: CH.I/II, DUAL, ADD,
CHOP., INVERT and X-Y Operation
On depressing the
DUAL
pushbutton, two traces must
appear immediately. On actuation of the
Y-POS.
controls,
the trace positions should have no effect on each other.
Nevertheless, this cannot be entirely avoided, even in fully
serviceable instruments. When one trace is shifted
vertically across the entire screen, the position of the
other trace must not vary by more than 0.5mm.
A criterion in chopped operation is trace widening and
shadowing around and within the two traces in the upper
or lower region of the screen. Set
TIME/DIV.
switch to
2µs/div.
, depress the
DUAL
and
CHOP.
pushbutton, set
input coupling of both channels to
GD
and advance the
INTENS.
control fully clockwise. Adjust
FOCUS
for a
sharp display. With the
Y-POS.
controls shift one of the
traces to a +2div., the other to a
−
2div. vertical position
from the horizontal center line of the graticule. Do not try
to synchronize (with the time variable control) the chop
frequency (0.5MHz)! Then alternately release and depress
the
CHOP.
pushbutton. Check for negligible trace widening
and periodic shadowing in the chopped mode.
It is important to note that in the
I+II
add mode (only
ADD
depressed) or the
I–II
difference mode (
INVERT CHII
button depressed in addition) the vertical position of the
trace can be adjusted by using
both
the Channel I and
Channel II
Y-POS.
controls.
In X-Y Operation (
XY
pushbutton depressed), the sensitivity
in both deflection directions will be the same. When the
signal from the built-in square-wave generator is applied to
the input of Channel II, then, as with Channel I in the vertical
direction, there must be a horizontal deflection of
4div.
when
the deflection coefficient is set to
50mV/div.
position (varia-
ble control set to its
CAL.
position,
X-MAG. (x10)
button in
out position). The check of the mono channel display with the
CHI/II
button is unnecessary; it is contained indirectly in the
tests above stated.
input of the vertical amplifier (e.g. using a
x1 probe
), the
displayed signal in the
50mV/div.
position (variable control
to
CAL.
) should be
4div.
high (
DC
input coupling). Maximum
deviations of 0.12div. (3%) are permissible. If a
x10 probe
is
connected between the
2V
output and Y input, the same
display height should result. With higher tolerances it should
first be investigated whether the cause lies, within the
amplifier or in the amplitude of the square-wave signal. On
occasions it is possible that the probe is faulty or incorrectly
compensated. If necessary the measuring amplifier can be
calibrated with an accurately known DC voltage (
DC
input
coupling). The trace position should then vary in accordance
with the deflection coefficient set.
With variable control at the attenuator switch fully conter-
clockwise, the input sensitivity is decreased at least by
the factor 2.5 in each position. In the
50mV/div.
position,
the displayed calibrator signal height should vary from
4div. to at least 1.6div.
Transmission Performance of the
Vertical Amplifier
The transient response and the delay distortion correction
can only be checked with the aid of a square-wave
generator with a fast risetime (
max. 5ns
). The signal
coaxial cable (e.g. HZ34) must be terminated at the
vertical input of the oscilloscope with a resistor equal to
the characteristic impedance of the cable (e.g. with
HZ22). Checks should be made at 100Hz, 1kHz, 10kHz,
100kHz and 1MHz, the deflection coefficient should be
set at
5mV/div.
with
DC
input coupling (Y variable control
in
CAL.
position). In so doing, the square pulses must have
a flat top without ramp-off, spikes and glitches; no
overshoot is permitted, especially at 1MHz and a display
height of
4-5div.
. At the same time, the leading top corner
of the pulse must not be rounded. In general, no great
changes occur after the instrument has left the factory,
and it is left to the operators discretion whether this test
is undertaken or not. A suited generator for this test is
HZ60 from HAMEG.
Of course, the quality of the transmission performance is
not only dependent on the vertical amplifier.
The input
attenuators
, located in the front of the amplifier,
are
frequency-compensated in each position
. Even small
capacitive changes can reduce the transmission
performance. Faults of this kind are as a rule most easily
detected with a square-wave signal with a low repetition
rate (e.g. 1kHz). If a suitable generator with max. output
of 40V
pp
is available, it is advisable to check at regular
intervals the deflection coefficients on all positions of the
input attenuators and readjust them as necessary. A
compensated
2:1 series attenuator
(e.g. HZ23) is also
necessary, and this must be matched to the input
impedance of the oscilloscope. This attenuator can be
