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Test Instructions
General
These Test Instructions are intended as an aid for checking
the most important characteristics of the HM 203-7 at regu¬
lar intervals without the need for expensive test equipment.
Resulting corrections and readjustments inside the instru¬
ment, indicated by the following tests, are described in the
Service Instructions or on the Adjusting Plan. They should
only be undertaken by qualified personnel.
As with the First Time Operation instructions, care should
be taken that all knobs with arrows are set to their calibrated
positions. None of the pushbuttons should be depressed.
TRIG, selector switch to AC, TV SEP. switch to OFF. It is
recommended to switch on the instrument for about 15
minutes prior to the commencement of any check.
Cathode-Ray Tube: Brightness and Focus,
Linearity, Raster Distortions
Normally, the CRT of the HM 203-7 has very good bright¬
ness. Any reduction of this brightness can only be judged
visually. However, decreased brightness may be the result
of wrong setting or reduced high voltage. The latter is easily
recognized by the greatly increased sensitivity of the verti¬
cal amplifier. Right setting means, that the HOLDOFF con¬
trol should be turned to the left stop; the X-MAG. xlO but¬
ton should be released; a medium time coefficient should
be selected; line triggering (~ position) should be used only
with a suitable TIME/DIV. switch setting (e.g. 2ms/div.).
The control range for maximum and minimum brightness
(intensity) must be such that the beam just disappears
before reaching the left hand stop of the INTENS. control
(particularly when the X-Y button is depressed), while with
the control at the right hand stop the focus and the line
width are just acceptable.
With maximum intensity the timebase fiy-back must
on no account be visibie.
Visible trace fault without input
signal: bright dot on the left side
— or -
decreasing bright¬
ness from left to right or shortening of the baseline. (Cause;
Incorrect Unblanking Pulse.) It should be noted that with
wide variations in brightness, refocusing is always neces¬
sary. Moreover, with maximum brightness, no "pumping"
of the display must occur. If pumping does occur, it is nor¬
mally due to a fault in the regulation circuitry for the high
voltage supply. The presetting pots for the high voltage cir¬
cuit, minimum and maximum intensity, are only accessible
inside the instrument (see Adjusting Plan and Service
Instructions).
A certain out-of-focus condition in the edge zone of the
screen must be accepted. It is limited by standards of the
CRT manufacturer. The same is valid for tolerances of the
orthogonality, the undeflected spot position, the non-linear¬
ity and the raster distortion in the marginal zone of the
screen in accordance with international standards (see CRT
data book). These limit values are strictly supervised by
HAM EG. The selection of a cathode-ray tube without any
tolerances is practically impossible.
Astigmatism Check
Check whether the horizontal and vertical sharpness of the
display are equal. This is best seen by displaying a square-
wave signal with the repetition rate of approximately
1 MHz. Focus the horizontal tops of the square-wave signal
at normal intensity, then check the sharpness of the vertical
edges. If it is possible to improve this vertical sharpness by
turning the FOCUS control, then an adjustment of the astig¬
matism control is necessary. A potentiometer of 47 kQ is
provided inside the instrument for the correction of astig¬
matism (see Service Instructions). A certain loss of marginal
sharpness of the CRT is unavoidable; this is due to the man¬
ufacturing process of the CRT.
Symmetry and Drift of the Vertical Amplifier
Both of these characteristics are substantially determined
by the input stages of the amplifiers.
The symmetry of both channels and the vertical final
amplifier can be checked by inverting Channel I and II (de¬
press the corresponding INVERT pushbutton). The vertical
position of the trace should not change by more than 0.5div.
However, a change of 1 div. is just permissible. Larger
deviations indicate that changes have occurred in the
amplifier.
A further check of the vertical amplifier symmetry is possi¬
ble by checking the control range of the Y-POS. controls. A
sine-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 approx¬
imately
8div.,
the upper and lower positions of the trace
that are visible should be approximately of the same height.
Differences of up to 1 div. are permissible (input coupling
should be set to AC).
Checking the drift is relatively simple. 15 minutes 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
O.Sdiv.
during the following
hour.
Calibration of the Vertical Amplifier
Two square-wave voltages of
0.2 Vpp
and
2Vpp
±1 % are pre¬
sent at the output eyelets of the calibrator (CAL.) If a direct
Subject to change without notice
T1 203-7
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