Hameg HM303-6 User manual

Release: December, 2007
35 MHz
Analog Oscilloscope
HM303-6
Servicemanual
English

2Subject to change without notice
General information regarding the CE marking
HAMEG instruments fulfill the regulations of the EMC directive. The
conformity test made by HAMEG is based on the actual generic- and
product standards. In cases where different limit values are applicable,
HAMEG applies the severer standard. For emission the limits for
residential, commercial and light industry are applied. Regarding the
immunity (susceptibility) the limits for industrial environment have
been used.
The measuring- and data lines of the instrument have much influence
on emission and immunity and therefore on meeting the acceptance
limits. For different applications the lines and/or cables used may
be different. For measurement operation the following hints and
conditions regarding emission and immunity should be observed:
1. Data cables
For the connection between instrument interfaces and external devices,
(computer, printer etc.) sufficiently screened cables must be used.
Without a special instruction in the manual for a reduced cable length,
the maximum cable length of a dataline must be less than 3 meters and
not be used outside buildings. If an interface has several connectors
only one connector must have a connection to a cable.
Basically interconnections must have a double screening. For IEEE-bus
purposes the double screened cables HZ73 and HZ72L from HAMEG
are suitable.
2. Signal cables
Basically test leads for signal interconnection between test point and
instrument should be as short as possible. Without instruction in the
manual for a shorter length, signal lines must be less than 3 meters
and not be used outside buildings.
Signal lines must screened (coaxial cable - RG58/U). A proper ground
connection is required. In combination with signal generators double
screened cables (RG223/U, RG214/U) must be used.
3. Influence on measuring instruments
Under the presence of strong high frequency electric or magnetic
fields, even with careful setup of the measuring equipment, influence
of such signals is unavoidable.
Die HAMEG Instruments GmbH bescheinigt die Konformität für das Produkt
The HAMEG Instruments GmbH herewith declares conformity of the product
HAMEG Instruments GmbH déclare la conformite du produit
Bezeichnung / Product name / Designation:
Oszilloskop
Oscilloscope
Oscilloscope
Typ / Type / Type: HM303-6
mit / with / avec: –
Optionen / Options / Options: –
mit den folgenden Bestimmungen / with applicable regulations / avec les
directives suivantes
EMV Richtlinie 89/336/EWG ergänzt durch 91/263/EWG, 92/31/EWG
EMC Directive 89/336/EEC amended by 91/263/EWG, 92/31/EEC
Directive EMC 89/336/CEE amendée par 91/263/EWG, 92/31/CEE
Niederspannungsrichtlinie 73/23/EWG ergänzt durch 93/68/EWG
Low-Voltage Equipment Directive 73/23/EEC amended by 93/68/EEC
Directive des equipements basse tension 73/23/CEE amendée par 93/68/CEE
Angewendete harmonisierte Normen / Harmonized standards applied / Normes
harmonisées utilisées:
Sicherheit / Safety / Sécurité: EN 61010-1:2001 (IEC 61010-1:2001)
Überspannungskategorie / Overvoltage category / Catégorie de surtension: II
Verschmutzungsgrad / Degree of pollution / Degré de pollution: 2
Elektromagnetische Verträglichkeit / Electromagnetic compatibility /
Compatibilité électromagnétique
EN 61326-1/A1 Störaussendung / Radiation / Emission:
Tabelle / table / tableau 4; Klasse / Class / Classe B.
Störfestigkeit / Immunity / Imunitée:Tabelle / table / tableau A1.
EN 61000-3-2/A14 Oberschwingungsströme / Harmonic current emissions /
Émissions de courant harmonique:
Klasse / Class / Classe D.
EN 61000-3-3 Spannungsschwankungen u. Flicker / Voltage fluctuations and flicker /
Fluctuations de tension et du flicker.
Datum /Date /Date
01. 04. 2007
Unterschrift / Signature / Signatur
Holger Asmussen
Manager
This will not cause damage or put the instrument out of operation. Small
deviations of the measuring value (reading) exceeding the instruments
specifications may result from such conditions in individual cases.
4. RF immunity of oscilloscopes.
4.1 Electromagnetic RF field
The influence of electric and magnetic RF fields may become visible
(e.g. RF superimposed), if the field intensity is high. In most cases
the coupling into the oscilloscope takes place via the device under
test, mains/line supply, test leads, control cables and/or radiation.
The device under test as well as the oscilloscope may be effected by
such fields.
Although the interior of the oscilloscope is screened by the cabinet,
direct radiation can occur via the CRT gap. As the bandwidth of
each amplifier stage is higher than the total –3dB bandwidth of the
oscilloscope, the influence of RF fields of even higher frequencies
may be noticeable.
4.2 Electrical fast transients / electrostatic discharge
Electrical fast transient signals (burst) may be coupled into the
oscilloscope directly via the mains/line supply, or indirectly via test
leads and/or control cables. Due to the high trigger and input sensitivity
of the oscilloscopes, such normally high signals may effect the trigger
unit and/or may become visible on the CRT, which is unavoidable.
These effects can also be caused by direct or indirect electrostatic
discharge.
HAMEG Instruments GmbH
Hersteller HAMEG Instruments GmbH KONFORMITÄTSERKLÄRUNG
Manufacturer Industriestraße 6 DECLARATION OF CONFORMITY
Fabricant D-63533 Mainhausen DECLARATION DE CONFORMITE

3
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Contents
Analog Oscilloscope HM303-6 4
Specifications 5
Front Panel Elements – Brief Description 6
Short Description of HM303-6 Boards 9
1 YP Board 9
2 XY Board 9
3 TB Board 10
4 CR Board 10
5 CC Board 10
6 FC Board 11
7 PS Board 11
PCB Interconnections 12
Board Replacement 14
1 PS Board 14
2 FC Board 15
3 CC Board 17
4 YP Board 17
5 XY Board 18
6 TB Board 19
7 CR Board 20
HM303-6 Troubleshooting 21
Security advice! 21
1 Opening the Oscilloscope 21
2 Preliminary Tests 22
3 Error Diagnostics! 25
Performance Check HM303-6 31
A Test Instruments required 31
B Basic Settings 31
C Checks 31
Spare-Part List HM303-6 38
Adjustment Procedere HM303-6 39

4Subject to change without notice
HM303-6
35 MHz Analog Oscilloscope
HM303-6
2 Channels with deflection coefficients of 1 mV/cm – 20 V/cm
Time Base: 0.2 s/cm – 100 ns/cm,
with X Magnification to 10 ns/cm
Low Noise Measuring Amplifiers with high pulse fidelity
and minimum overshoot
Triggering from 0 to 50 MHz from 5 mm signal level
(up to 100 MHz from 8 mm)
Up to 500,000 signal displays per second
in optimum analog quality
Yt, XY and component-test modes
Line triggered composite
video signal
No signal distortion
resulting from overshoot
Full screen display of
35 MHz sine wave signal

5
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HM303-6 Specifications
35 MHz Analog Oscilloscope HM303-6
Valid at 23 °C after a 30 minute warm-up period
Vertical Deflection
Operating Modes: Channel I or II only
Channels I and II (alternate or chopped)
Sum or Difference of CH I and CH II
Invert: CH II
XY Mode: via CH I (X) and CH II (Y)
Bandwidth: 2 x 0 to 35 MHz (-3 dB)
Rise Time: ‹10ns
Overshoot: max. 1%
Deflection Coefficients: 1-2-5 Sequence
1 mV/div. – 2 mV/div.: ± 5 % (Bandwidth 0 – 10 MHz (-3 dB))
5 mV/div. – 20 V/div.: ± 3% (Bandwidth 0 – 35 MHz (-3 dB))
Variable (uncalibrated): › 2.5 : 1 to › 50 V/div.
Input Impedance: 1 MΩ II 20 pF
Input Coupling: DC, AC, GND (ground)
Max. Input Voltage: 400 V (DC + peak AC)
Triggering
Automatic (Peak to Peak): 20 Hz – 50 MHz (≥5 mm)
50 MHz - 100 MHz (≥8 mm)
Normal with Level Control: 0 - 50 MHz (≥5 mm)
50 MHz – 100 MHz (≥8 mm)
Trigger Indicator: LED
Slope: positive or negative
Sources: Channel I or II, CH I / CH II alternate
(≥8 mm), Line and External
Coupling: AC: 10 Hz – 100 MHz
DC: 0 – 100 MHz
LF: 0 – 1.5 kHz
Trigger Indicator: LED
External Trigger Signal: ≥0.3 Vpp (30 Hz – 50 MHz)
Active TV sync. separator: pos. and neg.
Horizontal Deflection
Time Base: 0.2 s/div. – 0.1 μs/div. (1-2-5 Sequence)
Accuracy: ±3%
Variabel (uncalibrated): › 2.5:1 to › 0.5 s/div.
X Magnification x 10: up to 10ns/div.
Accuracy: ± 5 %
Hold-Off Time: variable to approx. 10 : 1
XY
Bandwidth X Amplifier: 0 – 2.5 MHz (-3 dB)
XY Phase shift ‹ 3°: ‹ 120 kHz
Component Tester
Test Voltage: approx. 7 Vrms (open circuit)
Test Current: max. 7 mArms (short-circuit)
Test Frequency: approx. 50 Hz
Test Connection: 2 banana jacks 4 mm Ø
One test circuit lead is grounded via protective earth (PE)
Miscellaneous
CRT: D14-363GY, 8 x 10 cm with internal graticule
Acceleration Voltage: approx. 2 kV
Trace Rotation: adjustable on front panel
Calibrator Signal (Square Wave): 0.2 V ± 1 %, ≈ 1 kHz/1 MHz (tr ‹ 4 ns)
Power Supply (Mains): 105 – 253 V, 50/60 Hz ± 10 %, CAT II
Power Consumption: approx. 36 Watt at 230 V/50 Hz
Ambient temperature: 0° C...+ 40° C
Safety class: Safety class I (EN61010-1)
Weight: approx. 5.4 kg
Dimensions (W x H x D): 285 x 125 x 380 mm
Accessories supplied: Line Cord, operator’s manual, 2 Probes 1:1 / 10:1 (HZ154)
HM303-6E/140907/ce · Subject to alterations · © HAMEG Instruments GmbH · ® Registered Trademark · DQS-certified in accordance with DIN EN ISO 9001:2000, Reg.-No.: DE-071040 QM
HAMEG Instruments GmbH · Industriestr. 6 · D-63533 Mainhausen · Tel [phone] · Fax [phone] · www.hameg.com · [e-mail]
A Rohde & Schwarz Company
www.hameg.com

6Subject to change without notice
Front Panel Elements – Brief Description
Specifications
Element Function
POWER Turns scope on and off.
(pushbutton + LED) LED indicates operating
condition.
INTENS Intensity control
(knob) for trace brightness
TRACE ROTATION To align trace with horizontal
(potentiometer; graticule line. Compensates
adjustment with influence of earth’s magnetic
screwdriver) field.
FOCUS Focus control for
(knob) trace sharpness.
Y-POS. I Controls vertical position
(knob) of channel I display.
Inoperative in X-Y mode.
Y MAG. x5 When depressed, increasing of
(pushbutton switch) Y-sensitivity CH I 5 fold (max.
1mV/div.)
Y MAG. x5 When depressed, increasing of
(pushbutton switch) Y-sensitivity CH II 5 fold (max.
1mV/div.)
Y-POS. II Controls vertical position
(knob) of channel II display.
SLOPE Selects the slope of the trigger
signal.
Element Function
SLOPE / = rising edge;
(pushbutton switch) \ = falling edge.
TR LED lights, if sweep is triggered.
(LED)
LEVEL Adjustment of trigger level.
(knob)
X-POS. Controls horizontal
(knob) position of trace.
X-MAG. x10 10:1 expansion in the X direction.
(pushbutton switch) Max. resolution 10ns/div.
(inoperative in XY-mode).
VOLTS/DIV. Channel I input attenuator.
(12 position Selects Y input sensitivity
rotary switch) in mV/div. or V/div.
in 1-2-5 sequence.
VAR. GAIN Fine adjustment of Y amplitude
(knob) CH I. Increases attenuation factor
min. by 2.5 (left hand stop).
For amplitude measurement
must be in CAL. position
(right hand stop).
CH I/II-TRIG. I/II No button depressed: CH I only
(pushbutton switch) and triggering from channel I.
When depressed, channel II only
and triggering from channel II.
(Trigger selection in DUAL
mode).

7
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Front Panel Elements – Brief Description
Element Function
DUAL Button released:
one channel only.
(pushbutton Button depressed: channel I
switch) and channel II in alternating
mode.
CHOP. DUALandADDbuttonsdepressed:
CH I and CH II in chopped mode.
ADD ADD depressed only:
(pushbutton switch) algebr. addition.
In combination with INV.:
difference.
VOLTS/DIV. Channel II input attenuator.
(12 position Selects Y input sensitivity
rotary switch) in mV/div. or V/div.
in 1-2-5 sequence.
VAR. GAIN Fine adjustment of Y amplitude
(knob) CH II. Increases attenuation
factor min. by 2.5 (left hand stop).
For amplitude measurement
must be in CAL. position (right
hand stop).
TRIG. MODE Trigger selector:
(switch) AC: 10Hz-100MHz.
AC-DC-LF-TV DC: DC-100MHz.
LF: DC-1.5kHz.
TV: Triggering for frame and line.
AT/NM Button released = autom. trig.
(pushbutton trace visible without input signal.
switch) Button depressed = normal trig.
with LEVEL adjustment.
~AT/NM and ALT pushbuttons
depressed:
Internal line triggering in combi-
nation with normal triggering.
ALT Triggering alternates between
(pushbutton switch) CH I and CH II in alternating
DUAL Channel mode only.
HOLD OFF Controls holdoff-time
(knob) between sweeps.
Normal position = full ccw.
TIME/DIV. Selects time coefficients
(rotary switch) (speeds) of time base,
from 0.2s/div. to 0.1µs/div.
Variable Variable adjustment of time base.
time base control Decreases time deflection speed
(center knob) at least 2.5 fold.
For time measurements
turn to right hand stop.
Element Function
XY Selects X-Y operation,
(pushbutton switch) stops sweep.
X signal via CH I.
Attention!
Phosphor burn-in without signal.
TRIG. EXT. Button released = internal trig.
(pushbutton switch) Button depressed = external
triggering, trigger signal via TRIG.
EXT. BNC socket.
INPUT CH I Channel I signal input and input
(BNC socket) for horizontal deflection in X-Y
mode.
Input impedance 1MΩ II 20pF.
AC-DC Selects input coupling of CH I
(pushbutton switch) vertical amplifier.
DC = direct coupling
AC = coupling via capacitor.
GD GD = signal disconnected
(pushbutton switch) from input, Y amplifier grounded.
Connector for reference potential
(4mm socket) (galvanically connected to earth).
INPUT CH II CH II signal input.
(BNC socket) Input impedance 1MΩ II 20pF.
AC-DC Selects input coupling of the CH II
(pushbutton switch) vertical amplifier. Specs see (29).
GD GD = signal disconnected
(pushbutton switch) from input, Y amplifier grounded.
INV. Inversion of CH II display.
(pushbutton switch) In combination with ADD button
= difference CH I, CH II.
TRIG. EXT. Input for external trigger signal.
(BNC socket)
(Pushbutton TRIG. EXT. depressed.)
COMP. TESTER Switch to convert oscilloscope
(pushbutton switch) to component tester mode.
Release X-MAG. X10 pushbutton.
COMP. TESTER Connectors for test leads
(4mm sockets) of the Component tester.
0.2Vpp Calibrator square wave output
(test socket) 0,2Vpp.
CALIBRATOR
1kHz/1MHz Selects calibrator frequency.
(pushbutton switch) Button released: approx. 1kHz,
Button depressed: approx. 1MHz.

8Subject to change without notice
Blockdiagram
MB Board
CR Board
PS Board
XY Board
YP Board
HM303-6 Block diagram
FC Board
TB Board
CC Board
CH 1 CH 2
Ext.Trig.
/2
/2
/2
/2/2
/2/2
Impedance
Converter
(FET)
Buffer
Pre-
Amplifier
*1 / *5
Attenuator
4 : 1 2 : 1 1 : 1
Attenuator
100 : 1
10 : 1
1 : 1
Instrument
Control
Calibrator
Impedance
Converter
(FET)
Buffer
Input
Coupling
AC / DC
GND
Var.
Gain
Intermediate
Trigger
CH1
Amplifier
Intermediate
Trigger
CH2
Amplifier
Symmetry
&
Trigger
Pick Off
Trigger
Channel
Switch
CH1
Trigger
Channel
Switch
CH2
Trigger
Amplifier
(Sync. Amp.)
Intermediate
Amplifier
Y-Pos
Control
LF
Filter
Impedance
Converter
(FET)
Buffer
Pre-
Amplifier
*1 / *2
Attenuator
4 : 1 2 : 1 1 : 1
Attenuator
100 : 1
10 : 1
1 : 1
Input
Coupling
AC / DC
GND
Var.
Gain
Symetrie
&
Trigger
Pick Off
Inverting
Switch
Intermediate
Amplifier
Y-Pos
Control
Trigger
Comparator
Channel
Mode
Control
Trigge r
Buffer
Channel
Switch
CT
Switch
Y Final
Amplifier
X Final
Amplifier
& X-Pos.
Control
Focus
Control
Blanking
Switch
&
Amplifier
Astigmatism
Adjust
TB
XY CT
Switch
Trigger
Channel
Switch
External
AC / DC
Select
& Line
P–P
Trigger
&
Level Control
Component
Tester
Blanking
Amplifier
&
Intens
Hold Off
Generator
&
Comperator
TV Sync.
Separator
&
TV Slope
Selection
Time Base
Control
AT/NM
Trigger
Sawtooth
Generator
(TB) &
Comperator
Power
Supply
HV
Generator
/2/2/2/2
/2
/2
Line / Mains
/2
/2/2/2
/2

9
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Short Description of HM303-6 Boards
Short Description of HM303-6 Boards
Preliminary note:
This short description refers to the HM303-6 block diagram. It
contains the most important functions, but not all.
1 YP Board
1.1 CH1 and CH2
1.1.1 Input, High Impedance Attenuator and FET impedance
converter
The measuring signal at the input is connected to the AC/DC
coupling switch. Opposite to DC coupling, in AC coupling mode
the DC signal content is blocked.
With GND not activated, the signal bypasses the GND (ground
switch) into a switchable high impedance (1 MΩ) attenuator
and enters a FET (impedance converter). If GND is selected,
the signal path is interrupted and attenuator or FET input are
grounded.
1.1.2 Pre-Amplifier
The next stage is the Pre-Amplifier where an additional
amplification by 5 is made to enable 1 mV/cm and 2 mV/cm
sensitivity.
1.1.3 Low Impedance Attenuator
The following selectable low impedance attenuators (1:1, 2:1
and 4:1); the high impedance attenuator and the Pre-Amplifier
enable the selection of all Y deflection coefficients from 1
mV/cm to 20 V/cm.
1.1.4 Variable Gain and Symmetry
In the next stage (VAR. GAIN) the fixed Y deflection coefficient
can also be set to uncalibrated intermediate values; unba-
lance can be compensated by variable balance adjustment
(VAR_BAL). Additionally the signal is converted in this stage
from an unsymmetrical signal into 2 symmetrical signals with
a phase difference of 180°. The following stages are designed
as two identical symmetrical amplifiers.
1.1.5 Trigger Pick Off, Intermediate Amplifier Driver and
Invert CH II
In this stage the trigger signal is picked off and feeds the In-
termediate Trigger Amplifier. The signal at the emitter drives
the Intermediate Amplifier (channel II via the Inverting Switch).
When activated, the Inverting Switch interchanges the 2 (180°
different) measuring signals to be amplified in the following
stages. The result is a 180° turned (inverted) signal display.
Unbalance in the channel II stage can be compensated by the
invert balance adjustment (INV_BAL2).
1.1.6 Intermediate Amplifier
This amplifier follows the inverting switch. Here the DC current
of both identical amplifiers is controlled in such a way, that if
the current in one amplifier is reduced it increases in the other
amplifier by the same amount. This causes a trace position shift
in (Y position). Time constants between both emitters are for
amplifier frequency response correction.
1.1.7 Channel Switch
Thereafter the measuring signals of CH1 and CH2 are input
in the Channel Switch (diode switch) of each channel. Both
channel switch outputs are connected with the Y-Final Ampli-
fier on XY Board.
1.1.8 Channel Switch Control
Depending on the current channel mode (CH I, CH II, alterna-
ting DUAL, chopped DUAL, XY and CT (Component Tester)) the
channel switches are controlled by the Channel Mode Control
stage (IC2007). This IC also controls the trigger channel swit-
ches CH I, CH II (internal triggering) and external triggering
(TRIG. EXT.) and generates the chopper signal as well as the
chopper blanking signal.
1.2 Trigger Section
1.2.1 Intermediate Trigger Amplifier CH I
The CH I measuring signal originating from the measuring
amplifier (trigger pick off) is amplified in this amplifier (named
TRIG.-PICK-OFF in the circuit diagram). The same IC (2004)
acts as the Trigger Channel Switch CH I.
Amplifier unbalance in this stage can be compensated by DC-
Triggering adjustment (P2006).
1.2.2 Intermediate Trigger Amplifier CH II
The CH II measuring signal originating from the measuring
amplifier (trigger pick off) is amplified in this amplifier (named
TRIG.-PICK-OFF in the circuit diagram). The same IC (2005)
acts as the Trigger Channel Switch CH II.
Amplifier unbalance in this stage can be compensated by DC-
Triggering adjustment (P2008).
1.2.3 External Triggering
The signal for external triggering, originating from the TRIG.
EXT. input, passes a 2:1 divider and controls a FET (impedance
converter). In the next stage (IC2002) the signal is converted
from an unsymmetrical signal into 2 symmetrical signals with
a phase difference of 180° and enters the External Trigger
Channel Switch.
1.2.4 Trigger Source Selection
The Trigger Channel Switches are controlled by the Channel
Mode Control stage (IC2007). The signal to be used for trigge-
ring is output at one of the trigger channel switches, connected
with the Trigger Amplifier (Sync. Amp.) on TB Board.
2 XY Board
2.1 CT Switch
If CT mode is selected the channel switches CH I and CH II are
closed and the Y component of the COMPONENT TESTER signal
is input via the CT Switch in the following Y-Final-Amplifier.
2.2 Y Final Amplifier
The measuring signal is amplified and controls the Y plates of
the cathode ray tube (CRT).
2.3 TB XY CT Switch
This switch is controlled by the mode settings and has inputs
for the time base sawtooth signal, the X signal component in
XY mode and the X signal in CT (COMPONENT TESTER) mode.
One of these signals controls the X Final Amplifier.
2.4 X Final Amplifier & X-Pos. Control
The signal for X deflection is amplified and controls the X plates
of the cathode ray tube (CRT). The gain can be switched between
x1 and x10 X deflection.
A DC voltage originating from X-POS. control is also input. It
enables X position shift of the trace.

10 Subject to change without notice
Input signals are the trigger comparator signal, the tv sync.
pulses, the logic signals from sawtooth and hold off comparator
and the chopper blanking signal.
These signals and functions are controlled by the state of dif-
ferent modes such as trigger slope, automatic/normal trigger,
CT mode, XY mode and TV trigger settings.
3.9 Sawtooth Generator (TB) & Comparator
If the trigger conditions are met, the sawtooth generator is
activated so that a sawtooth is generated for X deflection -
deflecting the beam from left to right; additionally the beam
blanking is switched off so that the beam (trace) becomes
visible. The sawtooth speed depends on the time base switch
setting, which selects a capacitor to be charged by a selectable
constant current source and the time base variable control.
A voltage comparator output is connected with the time base
control circuit via a Flip-Flop (also connected with the hold
off comparator output). When the sawtooth maximum height
is reached, the sawtooth capacitor is discharged so that
the beam returns to the start position on the left side of the
screen. Additionally the blanking is switched on to make the
beam invisible during flyback and hold off time until the hold
off time has elapsed and the trigger circuit starts the sawtooth
generator again.
3.10 Hold Off Generator & Comparator
At the same time as the sawtooth is discharged, the hold off
generator is activated, and a capacitor is charged (time base
setting dependent). The purpose is to generate a waiting time
for beam flyback followed by a time in which triggering is
disabled. As the duration of the hold of f time is time base setting
dependent, it allows constant trace intensity at all time base
settings in automatic triggering condition, without signal.
A voltage comparator generates a signal when the hold off ca-
pacitor is charged to a certain value. The comparator output is
connected with the time base control circuit via a Flip-Flop (also
connected with the sawtooth comparator output). It generates
the signal for hold off capacitor discharge and prepares for the
next signal display which can only be caused by a trigger signal
in normal trigger mode. In automatic mode it can be caused
by a trigger signal but also by the automatic generator if no
trigger signal is present.
The hold off time can be increased by the HOLD OFF control
for pulse train triggering etc.
3.11 Blanking Amplifier & Intens
Blanking signal and the intensity control DC voltage are com-
bined in this stage and control the Blanking Switch & Amplifier
stage on CR Board.
4 CR Board
The CR board contains the Blanking Final Amplifier, the Blan-
king Switch & Amplifier, the Focus Control and the Astigmatism
Adjust. stage.
5 CC Board
5.1 CALIBRATOR Signal
The 0.2 Vpp calibrator signal is generated for probe adjustment
purposes. It is a square wave signal that can be switched from
1 kHz (probe adaptation to the oscilloscope input capacity) to
1 MHz (probe high frequency adaptation to the oscilloscope
frequency response).
3 TB Board
3.1 Sync. Amp.
The signal originating from the trigger channel switches enters
this stage for additional amplification and to be changed from
a symmetrical to an unsymmetrical signal.
In XY mode the output signal – originating from CH I – is used
for X-Amplifier control.
3.2 LF Filter
If LF Trigger is selected a capacitor is connected between Sync.
Amp. output and ground to short the higher frequencies of the
trigger signal.
3.3 AC/DC Select & Line
The Sync. Amp. output signal can pass this stage via a capa-
citor (AC coupling) if the AC switch is on or DC coupled if the
DC switch is on. In line/mains trigger mode both switches are
set to off and the line/mains trigger signal is introduced at the
output.
3.4 TV Sync. Separator & TV Slope Selection
The trigger signal originating from the Sync. Amp. output
passes a switch if TV triggering is selected and controls one of
two TV sync. pulse separator circuits; one designed for positive
and the other for negative polarity sync. pulses. With correct
slope selection, the relevant circuit separates the sync. pulses
from the picture content. At the output a capacitor is switched
to ground if time base settings suitable for frame triggering are
selected. The capacitor shorts the high frequency line trigger
pulses so that only the low frequency frame pulses appear at
the output. If time base settings are suitable for line triggering
the capacitor is switched off.
The output signal controls the Time Base Control AT/NM
Trigger IC (4008).
3.5 Trigger Buffer
The signal at the AC/DC Select & Line circuit output controls
the Trigger Buffer amplifier. The trigger signal at the Trigger
Buffer output is connected with the following 2 stages.
3.6 P-P Trigger & Level Control
In trigger and trigger coupling modes where Peak to Peak
triggering is used, the trigger signal is used to generate vol-
tages determining the minimum and maximum voltages for the
trigger level setting range. The trigger level can then be set
within these limits (trigger signal height dependent), so that the
trigger level is restricted to the signal height limits. Peak to
Peak triggering is only enabled in automatic triggering mode.
If normal (NM) triggering is selected or operating modes where
P-P triggering is switched off, the operating point of the P-P
circuit is set to fixed settings with positive and negative voltages
at the trigger level potentiometer that enable a level setting
over the full range.
The trigger level control DC voltage sets the operating point of
the trigger comparator.
3.7 Trigger Comparator
The trigger signal from the Trigger Buffer amplifier is compared
with the level control DC voltage in the trigger comparator and
generates a voltage change at the output each time the trigger
signal crosses the reference voltage.
The output signal controls the Time Base Control & AT/NM
Trigger stage.
3.8 Time Base Control & AT/NM Trigger
This circuit (IC4008) controls the sawtooth and the hold off gene-
rator, the automatic trigger generator and the trace blanking.
Short Description of HM303-6 Boards

11
Subject to change without notice
Short Description of HM303-6 Boards
5.2 COMPONENT TESTER
An oscillator generates the X and Y signal components (CTX
and CTY) of the component tester (CT) that can be changed
by applying electronic parts (e.g. semiconductors, resistors,
capacitors etc.) to the COMP. TESTER sockets.
6 FC Board
The switches and potentiometers on this board enable the user
to control the instrument.
7 PS Board
This board contains a switch mode power supply with different
supply voltages for the instrument.
It also contains a –2 kV high voltage generator required for ca-
thode ray tube (CRT) operation. The voltage for the CRT heater
is generated by separate, isolated windings of the switch mode
power supply transformer as it is connected with -2 kV.

12 Subject to change without notice
PCB Interconnections
J2003
J2005 J2004 J2006 J2007
J7004J7003
W9005 P9004 W9004
J2005
W9003 W9001 W9002
W6001
W6002
W6003
W4502
J1009
J1008
J1002
P4002 P4003
P4007 P4006
P4004 P4005
W6004
YP-Board
CR-Board
FC-Board XY-Board
CC-Board TB-Board
PS-Board
PCB Interconnections

13
Subject to change without notice
Interconnections between:
YP-Board (J2006) and FC-Board (J7003)
Direction Pin Name
1 GND
<-- 2 CH_1/2
<-- 3 ADD
<-- 4 DUAL
<-- 5 ALT/CHOP
<-- 6 ¯TR_EX¯
<-- 7 ¯ALT_TRIG¯
8 GND
<-- 9 Y2_POS
<-- 10 Y2/100
<-- 11 Y2/10
<-- 12 Y2/2
<-- 13 Y2/1
<-- 14 Y2x5
<-- 15 Y2_VAR
16 GND
<-- 17 Y1_POS
<-- 18 Y1/100
<-- 19 Y1/10
<-- 20 Y1/2
<-- 21 Y1/1
<-- 22 Y1x5
<-- 23 Y1_VAR
--> 24 -6V
--> 25 +5V
--> 26 +12V
YP-Board (J2007) and TB-Board (J4007)
Direction Pin Name
--> 1 ¯CT¯
--> 2 ¯XY¯
--> 3 CHBL
--> 4 ¯ALT_TRG¯
5 GND
<-- 6 AMP
YP-Board (J2004) and MB-Board (P4003)
Direction Pin Name
1 GND
--> 2 SY_1
--> 3 SY_2
4 GND
YP-Board (J2008) and XY-Board (W9003)
Direction Pin Name
<-- 1 +5V
<-- 2 +12V
<-- 3 -6V
YP-Board (J2003) and XY-Board (W9005)
Direction Pin Name
-> 1 no name (Y signal
to Y final amplifier)
2 GND
--> 3 no name (Y signal
to Y final amplifier)
FC-Board (J7004) and TB-Board (P4002)
Direction Pin Name
--> 1 LEVEL
--> 2 LL_P
--> 3 LL_N
--> 4 SLOPE_P/¯N¯
--> 5 DC_ON
--> 6 TV_ON
--> 7 LF_ON
--> 8 TRIG_AT/¯N¯
--> 9 AC_ON
--> 10 TR_LED
--> 11 ¯SR1¯
--> 12 SR2
--> 13 ¯LINE¯
--> 14 ¯SR5¯
--> 15 ¯XY¯
--> 16 ¯SR10¯
--> 17 ¯SC2¯
--> 18 ¯SH0¯
--> 19 ¯SC3¯
--> 20 T_VAR
--> 21 ¯X_MAG¯
--> 22 HOFF_VAR
--> 23 nc
--> 24 X_POS
--> 25 FOCUS
--> 26 INT_S
YX-Board (W9001) and TB-Board (P4006)
Direction Pin Name
<-- 1 +5V
<-- 2 LINE_TR
<-- 3 +12V
<-- 4 -CT_V
<-- 5 -6V
6 GND
XY-Board (W9004) and TB-Board (P4005)
Direction Pin Name
<-- 1 XY_X
<-- 2 ¯XY¯
<-- 3 XPOS
<-- 4 ¯CT¯
<-- 5 AS_X
<-- 6 ¯XMAG¯
XY-Board (P9003) and CR-Board (W6001)
Direction Pin Name
--> 1 no name (to X plate 1,
CRT)
<-- 2 nc
<-- 3 +146V (YDV)
<-- 4 +175V (XDV)
<-- 5 nc
--> 6 no name (to X plate 2,
CRT)
TB-Board (P9004) and CR-Board (W6002)
Direction Pin Name
--> 1 +12V
--> 2 Blank
3 GND
--> 4 FOC_CTRL
PS-Board (J1009) and CR-Board (W6003)
Direction Pin Name
--> 1 HT-2
--> 2 HT-1
--> 3 -2kV
--> 4 FOCUS
PS-Board (J1008) and CR-Board (W6004)
Direction Pin Name
1 50V
--> 2 PUMP_VOL
3 GND
XY-Board (W9002) and PS-Board (J1002)
Direction Pin Name
<-- 1 +175V
<-- 2 +146V
3 GND
<-- 4 +5.2V
<-- 5 LINE_TR
<-- 6 +12V
<-- 7 CT_V
<-- 8 -6V
PCB Interconnections

14 Subject to change without notice
Board Replacement
Preliminary note!
Although all PCBs have been tested by HAMEG, adjustment is
required after replacement, due to unavoidable tolerances.
PS Board
1 Before removing the PS board, check that the power cable
is not connected to the oscilloscope.
2 Remove the power rod from the power switch.
3 Press connector “A” and pull the ribbon cable (out).
4 Press connector “B” and pull the ribbon cable (out).
5 Remove the 5 screws marked “C” and remove the protection
(screening) shield.
6 Press connector “D” and pull the ribbon cable (out).
7 Remove the 3 nuts marked “E”.
Attention!
Do not unscrew the 3 screws marked “X” in fig. 1.5!
8 Remove screw and nut marked “F” (fig. 4 and 5).
Attention!
This screw connects the protective ground line with the
chassis.
After insertion of the new PS board, firstly this screw
must be used to connect the protective ground line with
the chassis. A secure connection must be made, which
can only broken by using a tool!
9 Replace the PS board and check that the isolation plate
between the PS board soldering side and the rear chassis
is still present. Then follow the previous instructions in
Board Replacement
1
2
3
4
5
PE

15
Subject to change without notice
Board Replacement
reverse order, but do not fit the protection (screening)
shield.
10 Measure the resistance between the power socket centre
connector marked “PE” and the rear chassis using an Ohm
meter. If the resistance is less than 1 Ohm continue the
fitting procedure. Otherwise check the protective earth
circuit, and repair it until the requirement of less than
1 Ohm between power socket PE and rear chassis is met.
11 Connect power cable to the oscilloscope and switch it on.
12 Follow the Adjustment Procedure HM303-6 in the following
order (item):
1) RV1001: Adjustment of +146 Volt supply
2) +175 Volt check
3) RV1003: Adjustment of +12 Volt supply
4) -6 Volt accuracy check
5) Y plate voltage check
13 Due to the influence of the supply voltages on all circuitry,
it is recommended to make a complete Performance Check
as described in this Service manual.
FC Board
1 Before removing the FC board, check that the power cable
is not connected to the oscilloscope.
– Turn the 3 variable knobs (arrow marking) from their ca-
librated detent to a position where the hexagon sockets
marked “A” - which may not have been accessible - can be
unfastened.
– Turn the 3 variable knobs (arrow marking) back to their
calibrated detent and unfasten the hexagon sockets marked
“B” which are accessible in this position.
– Remove the 3 variable knobs (now unfastened) together
with their shafts (the visible one marked “C”).
2 Remove all knobs and note that the FOCUS knob is the only
knob without marking.
3 Remove the power rod from the power switch and pull off
the red power pushbutton.
1
2
3
4

16 Subject to change without notice
4 Locate the long ribbon cable connecting the FC and the
YP board. Remove the glue (transport protection) from the
connector “B”, use a screwdriver as a lever and position it
in the gap to press the connector out while slightly pulling
at the ribbon cable.
Note!
Pulling at the ribbon cable or using a screwdriver at the
edges marked “X” may damage the plug.
5 Remove the short ribbon cable plug from the socket on the
TB board.
– Release the front panel mounting points on one side, using
a screwdriver as a lever.
– Turn the oscilloscope and release the front panel mounting
points as before.
– Carefully pull off the front panel.
6 Remove the 4 screws marked “C”.
7 Unsolder the trace rotation coil wires marked “D” and keep
the colour allocation in mind.
Attention!
Do not unscrew the 4 screws marked “X” in fig. 9!
8 Replace the FC board and follow the previous instructions
in opposite order.
Note!
Before inserting the variable knobs shafts, check that
the potentiometers are in calibrated detent position. The-
reafter insert the shafts completely and turn the variable
knobs clockwise until the arrow symbols point to the
right. Then fasten the shafts using the hexagon sockets
accessible in this position. Turn the variable knobs counter
clockwise (ccw) until the unfastened hexagon sockets can
be fastened.
9 Connect power cable to the oscilloscope and switch it on.
10 Due to tolerances of the potentiometers please follow the
instructions of the Adjustment Procedure HM303-6 in the
following order (item):
Board Replacement
5
6
7
8
9

17
Subject to change without notice
1) RV1001: Adjustment of +146 Volt supply
2) +175 Volt check
3) RV1003: Adjustment of +12 Volt supply
4) -6 Volt accuracy check
6) R6013: CRT minimum intensity
10) P2007: Y-Gain CH I at 5 mV/div
17) P2011: Y-Gain CH II at 5 mV/div
28) CV4001: 0.1 μs/div time base adjustment
29) RV4004: 50 μs/div time base adjustment
30) RV4003: 50 ms/div time base adjustment
34) RV4001: Trigger-Symmetry
40) VR7003: Trace Rotation Check
CC Board
1 Before removing the CC board, check that the power cable
is not connected to the oscilloscope.
2 Press connector “A” on XY board and pull the ribbon cable
(out).
3 Remove the 2 screws marked “B” and carefully pull the CC
board (out).
4 Replace the CC board and follow the previous instructions
in reverse order.
5 Connect power cable to the oscilloscope and switch it on.
6 Please follow the instructions of the Adjustment Procedure
HM303-6 in the following order (item):
1) RV1001: Adjustment of +146 Volt supply
2) +175 Volt check
3) RV1003: Adjustment of +12 Volt supply
4) -6 Volt accuracy check
40) VR7003: Trace Rotation check
41) RV4501: Component-Tester trace inclination
42) RV4502: Calibrator Output
YP Board
1 Before removing the YP board, check that the power cable
is not connected to the oscilloscope.
2 Press connector “A” and pull the ribbon cable (out).
3 Press connector “B” and pull the ribbon cable (out).
4 Remove the glue (transport protection) from the connector “C”,
use a screwdriver as a lever and position it in the gap to press
the connector out while slightly pulling at the ribbon cable.
Note!
Pulling at the ribbon cable or using a screwdriver at the
plug edges marked “X” may damage the plug.
5 Unsolder the YP board screening plate lugs “D” at the
position “E” and “F” and pull the plate to remove it.
1
2
Board Replacement
1
2

18 Subject to change without notice
6 Locate TB board, press connectors “A” and “B” and pull the
ribbon cables (out).
7 Unsolder the resistors at the BNC sockets “A”, “B” and “C”
and bend their leads away from the sockets.
8 Unsolder the 3 steel plate angles marked “D”, “E” and “F”
where soldered on the YP board.
9 Remove the nuts “A” and “B”.
10 Remove the screws “C” and “D”.
Attention!
Do not unscrew the 2 screws marked “X” in fig. 4!
– Lift the YP board at the rear so that the screws (where the
nuts “A” and “B” were mounted before) do not obstruct the
YP board removal.
– Replace the YP board and follow the previous instructions
in reverse order.
– Connect power cable to the oscilloscope and switch it on.
– Please follow the instructions of the Adjustment Procedure
HM303-6 and make a complete adjustment from item 1 to
item 42.
XY Board
1 Before removing the XY board, check that the power cable
is not connected to the oscilloscope.
2 Remove the power rod from the power switch.
3 Locate and identify TB board, press connectors “A” and pull
the ribbon cables (out).
4 Press connectors “A” and pull the ribbon cables (out).
3
4
Board Replacement
1
2
3

19
Subject to change without notice
5 After unscrewing the nuts “D”, accessible on the rear side
of the rear chassis, carefully remove the plastic screws “B”
and remove the white ceramic spacer discs (isolation and
heat sink).
6 Unsolder the 2 wires marked “A” on the bottom of the XY
board.
7 Replace the XY board and follow the previous instructions
in reverse order.
8 Connect power cable to the oscilloscope and switch it on.
9 Please follow the instructions of the Adjustment Procedure
HM303-6 in the following order (item):
1) RV1001: Adjustment of +146 Volt supply
2) +175 Volt check
3) RV1003: Adjustment of +12 Volt supply
4) -6 Volt accuracy check
10) P2007: YGain CH I at 5 mV/div
11) P2002: YGain CH II at 5 mV/div
25) P2012: ADDition balance
32) CV9001/9002, RV9006/9005: Y-Final Amplifier
38) Y-Amplifier Bandwidth Check
39) RV9001: Component-Tester Y-Offset
and
26) RV4005: Sawtooth start position
27) RV9004: X-Magnification x1
31) RV9003: X-Magnification x10
32) C9026, C9027: X-Magnification x10 linearity
33) RV9002: X-Gain Adjustment in XY-Mode
TB Board
1 Before removing the TB board, check that the power cable
is not connected to the oscilloscope.
2 Remove the power rod from the power switch.
3 Press connectors marked “A” and pull the ribbon cables
(out).
4 Pull connector “B” (out).
5 Remove the 4 screws marked “C”.
6 Replace the TB board and follow the previous instructions
in reverse order.
7 Connect power cable to the oscilloscope and switch it on.
Board Replacement
4
5
1
2

20 Subject to change without notice
8 Please follow the instructions of the Adjustment Procedure
HM303-6 in the following order (item):
1) RV1001: Adjustment of +146 Volt supply
2) +175 Volt check
3) RV1003: Adjustment of +12 Volt supply
4) -6 Volt accuracy check
9) RV4002: Focus control
34) RV4001: Trigger-Symmetry
35) P2006: DC-Triggering CH I
36) P2008: DC-Triggering CH II
26) RV4005: Sawtooth start position
27) RV9004: X-Magnification x1
28) CV4001: 0.5 μs/div time base adjustment
29) RV4004: 50 μs/div time base adjustment
30) RV4003: 50 ms/div time base adjustment
31) RV9003: X-Magnification x10
33) RV9002: X-Gain Adjustment in XY-Mode
CR Board
1 Before removing the CR board, check that the power cable
is not connected to the oscilloscope.
2 Locate and identify TB board, press connector “A” and pull
the ribbon cable (out).
3 Locate and identify XY board, press connector “A” and pull
the ribbon cable (out).
4 Locate and identify PS board, press connectors “A” and pull
the ribbon cables (out).
5 Unsolder soldering lug marked “B”.
6 Replace the CR board and follow the previous instructions
in reverse order.
7 Connect power cable to the oscilloscope and switch it on.
8 Please follow the instructions of the Adjustment Procedure
HM303-6 in the following order (item):
1) RV1001: Adjustment of +146 Volt supply
2) +175 Volt check
3) RV1003: Adjustment of +12 Volt supply
4) -6 Volt accuracy check
6) R6013: CRT minimum intensity
7) RV1005: Focus symmetry
8) R6024: Astigmatism correction
Board Replacement
1
2
3