switches on top of and beneath both main-PCBs. Further
more, the soldering connections of the 9 transistors and
Fixed Three-Terminal Regulators resp. on the rear
chassis. This visual inspection can lead to success much
more quickly than a systematic fault location using
measuring instruments. Prior to any extensive trouble
shooting, also check the external power source.
If the instrument fails completely, the first and most
important step —
after checking the mains/line voltage
and power fuse
— will be to measure the deflecting plate
voltages of the CRT. In almost any case, the faulty sec
tion can be located. The sections represent:
cuits (including the FETs). If a selected semiconductor is
defective, all gate-diodes or both push-pull transistors of
a stage should be replaced by selected components,
because otherwise there are possibly deviations of the
specified data or functions. The HAMEG Service Depart
ment can give you advice for troubleshooting and
replaceable parts. Replacement parts can be ordered by
letter or telephone from the nearest HAMEG Service Of
fice. Please supply the following information: Instrument
type and serial number, description of the part (including
function and location in the instrument), quantity desired.
Replacement of the Power Transformer
1 . Vertical deflection.
2. Horizontal deflection.
3. CRT circuit.
4. Power supply.
While the measurement takes place, the position controls
of both deflection devices must be in mid-position. When
the deflection devices are operating properly, the
separate voltages of each plate pair are almost equal then
(Y = + 85V and X = + 140V ). If the separate voltages of
a plate pair are very different, the associated circuit must
be faulty. An absent trace in spite of correct plate
voltages means a fault in the CRT circuit. Missing deflec
ting plate voltages is probably caused by a defect in the
power supply.
- 1 5 0 0 ... -1 6 5 0 V
G3
approx. —1935 V
L T L Z -i
- 1 8 7 8 V
900V
D1
approx. + 140V
D4*
approx. + 8 5 V
D3-
approx. + 8 5 V
G2, G4
approx. + 140V
approx. + 8 5 V
Voltages at the CRT socket
Replacement of Components and Parts
For the replacement of parts and components use only
parts of the same or equivalent type. Resistors without
specific data in the diagrams have a power dissipation of
0.25 Watt and a tolerance of 2%. Resistors in the high
voltage circuit must have sufficient electric strength.
Capacitors without a voltage value must be rated for an
operating voltage of 63V. The capacitance tolerance
should not exceed 20% . Many semiconductors are
selected, especially the gate-diodes 1N4154, and all
amplifier transistors, which are contained in push-pull cir-
Should it be necessary to replace the mains/line
transformer, the correct terminal sequence (color iden
tification) for primary and secondary windings must be
followed (see diagram "Power Supply" and the figure
below). In addition, the relevant Safety Regulations must
be observed. Here, we refer only to those requirements
relative to parts conductively connected to the supply
mains:
— The construction of the instrument shall be such as to
prevent any short-circuiting or bridging of the insula
tion, clearances or creepage distances between those
parts connected to the supply mains and any accessi
ble conductive parts due to accidental loosening or
freeing of the wiring, screws, etc.
— The rigidity of the mains wiring connections, which
may be subject to mechanical stresses, shall not be
dependent upon the soldering alone. To meet this
requirement, the bare ends of the wires must be
pushed through the holes in the respective soldering
tab, bent over with a pair of pliers, and subsequently
fixed by soldering.
— The minimum cross section of the protective earth
connection between the instrument's power inlet and
the connecting soldering tab on the rear chassis must
be 0.81m m 2 in North America and 0.75m m 2 in
Western Europe. The connecting soldering tab on the
rear chassis has to be secured mechanically against
loosening (e.g. with lock washer).
After replacing the power transformer, all remaining bits
of wire, solder and other foreign matter must be removed
from the PCBs, the vicinity of the power transformer and
from within the insulating connecting box by shaking,
brushing and blowing. Finally, the top plate of the
insulating connecting box has to be replaced. Before
connecting the instrument to the power supply, replace
the possibly defective fuse, press the
POWER
button and
make sure that there is an adequate insulation state
between chassis (= safety earth conductor) on the one
hand, and the live/line pin as well as the neutral pin, on
the other. Only after proper insulation has been estab
lished may further function tests with open chassis
follow, but with appropriate precautionary measures.
Please note Change Information,
if any, on last page.
S3 20 3-4
