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Service Instructions
General
The following instructions are intended as an aid for the
electronic technician, who is carrying out readjustments on
the HM 604, if the nominal values do not meet the specifica-
tions. These instructions primarily refer to those faults,
which were found after using the Test Instructions. How-
ever, this work should only be carried out by properly qual-
ified personnel. For any further technical information call or
write to HAMEG. Addresses are provided at the back of the
manual. It is recommended to use only the original packing
material, should the instrument be shipped to HAMEG for
service or repair (see also Warranty, page M2).
Instrument Case Removal
The rear cover can be taken off after unplugging the power
cord's triple-contact connector and after two cross reces-
sed pan head screws (M4x30mm) with two washers on it
have been removed. While the instrument case is firmly
held, the entire chassis with its front panel can withdrawn
forward. When the chassis is inserted into the case later on,
it should be noticed that the case has to fit under the flange
of the front panel. The same applies for the rear of the case,
on which the rear cover is put.
Caution
During opening or closing of the case, the instrument
must be disconnected from all power sources for
maintenance work or a change of parts or components.
If a measurement, trouble-shooting, or an adjustment
is unavoidable, this work must be done by a specialist,
who is familiar with the risk involved.
When the instrument is set into operation after the case
has been removed, attention must be paid to the accel-
eration voltage for the CRT - 12.5kV - and to the
operating voltages for both final amplifier stages -
together 14OV. Potentials of these voltages are on the
CRT socket, on the upper and the lower horizontal
neck. High voltages of max. 2000 V are at the INTENS.
and FOCUS potentiometers. They are highly dangerous
and therefore precautions must be taken. It should be
noted furthermore that shorts occuring on different
points of the CRT high voltage and unblanking circuitry
will definitely damage some semiconductors. For the
same reason it is very risky to connect capacitors to
these points while the instrument is on.
Capacitors in the instrument
when the instrument is disconnected from all voltage
sources. Normally, the capacitors are discharged 6 sec-
onds after switching ofi. However, with a defective
instrument an interruption of the load is possible.
Subject to change without notice
Therefore, atter switching off, it is recommended to con-
nect one by one all terminals of the check strip across
1 kQ to ground (chassis) for a period of 1 second.
Handling of the CRT needs utmost caution. The glass
bulb must not be allowed - under any circumstances -
to come into contact with hardened tools, nor should it
undergo local superheating (e.g. by soldering iron) or
local undercooling (e.g. by cryogenic-spray). We recom-
mend the wearing of safety goggles (implosion danger).
Operating Voltages
Besides the two AC voltages for the CRT heating (6.3V) and
graticule illumination, Component Tester and line triggering
v o l t a g e s g e n e r a t e d (+12V, +5V, -5V, -12V. +68V,
+ 14OV. - 18OOV, and + 10.4 kV). These different operating
voltages are fixed voltages, except the + 12V, which can be
adjusted. The variation of the fixed voltages greater than
is measured on the checkpoint strip (located on XY Board)
with reference to ground. Measurements of the high volt-
age may only be accomplished by the use of a sufficient
highly resistive voltmeter (>lOMQ). You must make abso-
lutely sure that the electric strength of the voltmeter is suf-
ficiently high.
Minimum Brightness
The variable resistor VR601, located on the Z-PCB, is used
for this adjustment procedure. It may only be touched by a
properly insulating screwdriver (Caution! High voltage!).
Correct adjustment is achieved, when the trace can be
blanked while X-Y pushbutton is depressed and, in addi-
tion, when the requirement described in the Test Instruc-
tions are met.
Astigmatism control
The ratio of vertical and horizontal sharpness can be
adjusted by the variable resistor VR603, located on the Z-
PCB (see Adjusting Plan). As a precaution however, the
voltage for the vertical deflecting plates (approx. +41.5V)
should firstly be checked, because this voltage will affect
the astigmastism correction. Use the 1 MHz square-wave
signal from the built-in calibrator via 10: 1 probe for this cor-
rection. Firstly adjust the sharpness of the horizontal
square-wave lines using the FOCUS control. The sharpness
of the verticallines should then be corrected with the aid of
be charged, even
the Astigm. pot VR626. Repeat the correction several
times in this sequence. Adjustment has been correctly car-
ried out when, on using FOCUS control only, the sharpness
is not improved in eitherdirection.
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