36
Subject to change without notice
wave signal of 10-100kHz is applied to the amplifier input.
When the
Y-POS.
control is then turned fully in both directions
from stop to stop with a display height of approximately 8div,
the upper and lower positions of the trace that are visible
should be approximately of the same height. Differences of up
to 1div are permissible (input coupling should be set to AC).
Checking the drift is relatively simple. 20minutes after switching
on the instrument, set the baseline exactly on the horizontal
center line of the graticule. The beam position must not
change by more than 0.5div during the following hour.
Calibration of the Vertical Amplifier
A square-wave voltage of 0.2Vpp ±1% is present at the output
socket of the calibrator (CAL.) If a direct connection is made
between the 0.2V output and the 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 (1%) is connected between the 0.2V output and Y input,
the deflection coefficient should be set to 5mV/div. Then the
maximum deviation is 0.16div.
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 in the attenuator sector fully counter-
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. 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
40Vpp 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 is also necessary, and this must be matched to the
input impedance of the oscilloscope. This attenuator can be
made up locally. It is important that this attenuator is shielded.
For local manufacture, the electrical components required are
a 1M
Ω
±1% resistor and, in parallel with it, a trimmer 3-15pF in
parallel with approx. 10pF. 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
In DUAL mode two traces must appear immediately. On
actuation of the Y-POS. controls, the trace positions should
have minimal 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 coefficient to 0.5ms/div,
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)! Check for negli-
gible trace widening and periodic shadowing when
switching between 0.5ms/div and 0.2ms/div.
It is important to note that in the I+II add mode or the I-II
difference mode 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, 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. The check of the mono channel
display is unnecessary; it is contained indirectly in the tests
above stated.
Triggering Checks
The internal trigger threshold is important as it determines the
display height from which a signal will be stably displayed. It
should be approx. 0.3-0.5div for the instrument. An increased
trigger sensitivity creates the risk of response to the noise
level in the trigger circuit. This can produce double-triggering
with two out-of-phase traces.
Alteration of the trigger threshold is not required. Checks can
be made with any sine-wave voltage between 50Hz and
1MHz. The instrument should be in automatic peak (value)
triggering (NM LED dark) and the
LEVEL
knob in electrical
midrange position. It should be ascertained whether the same
trigger sensitivity is also present with Normal Triggering (
NM
LED
lights). In this trigger mode, LEVEL adjustment is absolutely
necessary.
Test Instructions
