tion of the trace can be adjusted by using
both
the Chan
nel I and Channel II
Y-POS.
controls.
In X-Y Operation
(HOR. EXT.
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
4cm
when the deflection coeffi
cient is set to
50mV/cm
position (variable control set to
its
C
position,
X-MAGN. X5
button in out position). The
check of the mono channel display with the
C H I/II
but
ton is unnecessary; it is contained indirectly in the tests
above stated.
Triggering Checks
The internal trigger threshold is important as it deter
mines the display height from which a signal will be
stably displayed.
It should
be approx.
3-5m m
(frequency-dependent) for the HM203. An increased
trigger sensitivity creates the risk of response to the noise
level in the trigger circuit, especially when the sensitivity
of the vertical input is increased by turning the variable
control fully clockwise. This can produce double
triggering with two out-of-phase traces. Alteration of the
trigger threshold is only possible internally. Checks can
be made with any
sine-wave voltage
between 5 0 Hz and
1 MHz. The
AT/NORM.
button should be in out position
(Automatic Triggering). Following this it should be ascer
tained whether the same trigger sensitivity is also present
with Normal Triggering
(AT/NORM.
button depressed).
In this trigger mode, a
LEVEL
adjustment is necessary.
The checks should show the same trigger threshold with
the same frequency. On depressing the + / — slope but
ton, the start of the sweep changes from the positive
going to the negative-going edge of the trigger signal. As
described in the Operating Instructions, the trigger fre
quency range is dependent on the trigger coupling
selected. For higher frequencies, the
HF
coupling mode
must be selected. In this mode, triggering up to at least
40MHz (sine-wave) is possible. Internally the HM203
should trigger perfectly at a display height of approx.
5 mm, when the appropriate trigger coupling mode is set.
For external triggering
(TRIG. EXT.
button depressed),
the
TRIG. EXT.
input connector requires a signal voltage
of at least 0.6Vpp, which is in synchronism with the Y in
put signal. The voltage value is dependent on the fre
quency and the trigger coupling mode
(AC-DC-HF-LF).
Checking of the internal TV triggering is possible with a
video signal of any given polarity. In the
LF
position only,
reliable triggering on
frame
frequency is possible.
However, triggering on
line
(horizontal-scanning) fre
quency requires
AC
(possibly
DC)
trigger coupling. If no
video signal is available, the function of the
LF
position
(low-pass filter) can be checked using mains/line fre
quency or the built-in calibrator signal. With a mains/line
frequency signal (50-60Hz), switching from
AC
to
LF
trigger coupling should have no effect. In contrast, the
minimum signal voltage required for reliable triggering
should be at least double, when the 1 kHz calibration
signal is applied.
The display should not shift horizontally during a change
of the trigger coupling from
AC
to
DC
with a sine-wave
signal without DC offset. The basic requirement for this is
a correct
DC Balance Adjustment
on the input of the
vertical amplifier (see Operating Instructions, page M3).
If both vertical inputs are
AC
coupled to the same signal
and both traces are brought to coincide exactly on the
screen, when working in the
alternate dual channel
mode,
then no change in display should be noticeable,
when the
CHI/II
button is depressed or released.
Checking
of the
line/mains
frequency triggering
(50-60Hz) is possible, when the input signal is time-
related (multiple or submultiple) to the power line fre
quency
(TRIGGER SELECTOR
switch to
LINE).
In this
trigger mode, there is no trigger threshold. Even very
small input signals are triggered stably (e.g. ripple-
voltage). For the check, use an input of approx. 1 V from
a (separate) power transformer. The displayed signal
height can then be varied by turning the respective input
attenuator switch and its variable control.
Timebase
Before checking the timebase it should be ascertained
that the
trace length is precisely 10cm.
If not, it can be
corrected with the potentiometer for sweep amplitude
(see Adjusting Plan). This adjustment should be made
with the
TIMEBASE
switch in a mid-position (i.e.
50^s/cm).
Prior to the commencement of any check set
the time variable control to
C.
The
X-MAGN. X5
button
should be in out position. This condition should be main
tained until the variation ranges of these controls are
checked.
Check that the
sweep runs from the left to the right
side o f the screen
(TIMEBASE
switch to
200ms/cm;
X-POS.
control in mid-range). This check is only
necessary after changing the cathode-ray tube.
If a precise marker signal is not available for checking the
Timebase
time coefficients, then an accurate sine-wave
generator may be used. Its frequency tolerance should
not be greater than +1 %. The timebase accuracy of the
T3 20 3-4
