Philips PM 3342 User manual

PHILIPS
WiIUDi
PM
334
OUAI
T0.ACE
Y
AMPI
PM 3342 DUAL TRACE
UNIT
9499 440 04911
21 869
2 02 03

3
IMPORTANT
In correspondence
concerning this
apparatus, please
quote the type number
and the serial number
as given on
the type
plate at the
rear
of the
apparatus.

4
Contents
GENERAL
INFORMATION
XI. Checking and adjusting
26
I. Introduction 7
II. Technical data 7
A. General
information 26
III.
Description of
the
block
diagram 9
B. DC
balance
26
C. Levels of channels A
and
B
27
DIRECTIONS FOR USE
D.
Sensitivity of channels
A
and B
27
E.
AC -DC
switch; CHECK
ZERO 27
IV. Installation 11
F.
Square -wave response 27
V.
Controls and
their functions
13
G. Frequency response curve 29
VI. Applications 15
H. Defection
and shift 29
A. Amplitude measurements 15
B. Differential measurements 15
J.
Input attenuators
29
C. Phase measurements
16 K. Blocking of channels A
and
B
30
D.
Single time -base
16
L. Rejection factor 30
M.
Triggering
30
SERVICE NOTES
N.
Cho
in
pp~ g
31
VII.
Block diagram
17 O. Alternate 31
VIII. Vertical amplifier 23
XII. Parts lists 32
IX. Switching control -circuits
24
A. Mechanical
33
X.
Trigger amplifier
25
B. Electrical 34

5
List of figures
Fig. Page
1 Block diagram
9
2 Front view with
indication of controls and
connections
12
3
Block diagram (detailed)
19
4 Typical waveforms
22
5 Display
22
6 Right-hand view
26
7 TU-5
pulser
28
8 Left-hand
view
28
9
Measuring
probe,
directly
earthed
29
10 Input RC
standardiser
30
ll
Amplifier, channel A
38
12
Amplifier, channel B
39
13 Dual -trace unit
40
14 Output
amplifier
40
15
Trigger amplifier
41
16 Drift
compensator
41
17
Attenuator,
channel A
44
18
Attenuator, channel B
48
19
Trigger
-amplifier
circuit
52
20
Dual -trace circuit
56
21 Y
-amplifier
circuit
61

z
GENERAL INFORMATION
Introduction
0
The PM
3342
is a
dual
-trace
plug-in unit for
the
Y -
channel
of the PM 3330.
The unit contains
two
identical
amplifiers with an
electronic switch,
by
means of
which two signals can
be
compared
in
amplitude and
in
phase.
Technical
data
Note: Properties,
expressed
in numerical
values with
statement
of
tolerances are guaranteed by
the
factory. Numerical
values without tolerances
are
intended
for
information purposes only
and
indicate the properties
of an
average apparatus.
Input circuit
input
input
impedance
input
maximum
permissible
d.c. voltage
in
the a.c. position
Measuring probe
type
input
attenuation
permissible voltage
Amplifier
deflection coefficient
Moreover,
the sum and
the difference of two
input
signals can be displayed.
Trigger
of the
time base
occurs
at choice on one of
the
two input signals or on
the combined signal.
The
amplifier
data
apply
to channel A as well as
to
channel B.
adjustable AC or DC;
push-button for checking
the zero
level
1 MS2//15pF
BNC
400 V
PM 9331 A/10
10 MS2//8 pF
1 :
10,
tol.:
3%
1,OOOVpeak
adjustable to 10 calibrated values: 10,20, 50 mV/cm etc.,
up
to
10
V/cm; tolerance: 3%
continuous attenuator 1 :
3
(non
-calibrated)
bandwith D.C.:
0-50
Mc/s
A.C.:
1.6
c/s — 50 Mc/s
rise
-time 7 ns
rise time
of unit by itself: 5 ns
overshoot < 2%
rejection factor
>_ 100 x
for
frequencies <
1
Mc/s
in
position D.C. provided that the
amplifiers
are adjusted
to identical deflection -coefficients
maximum
common
mode input
signal corresponding
to
10
cm trace height
magnification
3
times useful screen
height,
symmetrical
round the centre
of
the
screen
for
frequencies up to
10
Mc/s.
The top of a
signal,
which is magnified at maximum, can be displayed
with
the
shift control.

8
polarity
phase difference
between both channels
Switching possibilities
externally
chopped
voltage
required
repetition frequency
rise time
input
capacitance
Trigger
mode
trace height required
in positions
DC,
LF
and
HF
in position AUT.
in positions
TV
LINE
and
TV FRAME
Mechanical data
reversible
not measurable
on the screen
1.
channel A
2.
channel B
3. channels A and B chopped; frequency 500 kc/s
or
20 kc/s
(internal
selection facility)
4. channels A
and
B alternately
5. channels
A
and
B
added
6. channels
A
and
B externally
chopped
symmetrical
square -wave voltage:
minimum, 1 V P
_p,
maximum, 20 V p
_ p
100 kc/s
1-100 ns
70 pF
A, B or A -~ B (in position "ADDED" only)
3 mm
for
frequencies up to
10
Mc/s
2 cm
for
frequencies up to
20
Mc/s
1 cm for frequencies up to 1 Mc/s
2 cm
dimension
width 15 cm
height 17.5 cm
length 29 cm (knobs
and
plug
included)
weight
3 kg
Accessories
1 Manual
Optional: 2 Measuring probes PM9331A/10

9
Description o f the block diagram
Channels A and B each consist of an
input circuit
in
which
the
"AC
-DC"
switch
and the step
attenuator
are
included., and
an amplifier which
containsthe V/cm
continuous
attenuator,
the
SHIFT control
and
the
polarity switch, see
Fig. 1.
The switching of
these
channels occurs
at the output
of
these
amplifiers, after which
the combined
signal
is
applied to
an
output
amplifier.
The
switching
circuit consists
of
a blocking
oscillator
A
0
CHECK
V/cm
A C
ZEORO
~DC
20 kHz
r - ~
I...i
i
500 kHz ~T'
MODE
A • t --
B •
CHOPPED •
ALTERNATE •
ADDED •
EXT.-CHOPPED
O
B
O AC~
DC
r --
b
DCBAL
Z
MOD
1
PM
3330
BLOCKING
OSCILLATOR
CATH
FOLL.
AMPLIFIER
and
a
bi-stable
multivibrator,
which
supplies the
switching
voltage. The trigger
voltage
for
the basic
oscilloscope is
taken
from
one
of
the channels via a
selector
switch.
A trigger
amplifier amplifies this
voltage, so that
the
trigger -
signal
and the
Y
-input
signal
have identical
amplitudes.
In position "ADDED"
of the "MODE" selector,
the
trigger
signal is directly taken from
the output
ampli-
fi
er.
NORMAL
INVERT
V'cm
CONT
I '
~ I SHIFT
b
GAIN
TRIGG
r
TRIGGER
AMPLIFIER
MULTIVIBRATOR
1
ELECTR.
SW
TCH
DCBAL
4
L_-
CHECK
ZERO
V
/ /CSR \
Fig. 1. Block
diagram
CATH
FOLL.
GAIN
V/cm
CONT
I
SHIFT
AMPLIFIER
NORMAL
INVERT
PEM
2633
I
FINAL —~
I Y-AMPL.
I
— ~1
I
POS. I
ADDED]
TRIGGER
O
I
PRE-AMPL.
STAGE

11
DIRECTIONS FOR USE
Installation
The
PM 3342 shculd
be plugged into the left
plug-in
compartment (Y -UNIT) of basic
oscilloscope
PM
3330.
Switching -on
is effected with the mains switch of the
basic
oscilloscope.
Approximately 10 minutes
after
switching -on,
the
unit has
reached its
operating
temperature and meets
the
technical
data.
When
using
the PM 3342, the switch
on
the
rear side
of
the
basic
oscilloscope should be set to
position
"MULTI -TRACE CHOPPER".

12
DN~tIDS
PM
334
DUAL
iRA~
SK8
,.-=.. ~ ate,,.. ~
SK6
S K 9 ---~
SK
10
Fig.
2.
Front view with indication of controls and connections

13
Controls and their functions
(Fig. 2) O
MODE selector SKS
~
~
~ i ~
~
~ ~ i i i i
~~
~~` ~~`
~ `~
~~
Trigger mode selector SK6
Input circuit
The
working mode
of
the
unit
can
be selected
with the
six -position
mode
selector.
channel A is
switched in,
channel B is out
of action
channel B is switched
in,
channel A is out
of action
CHOPPED
both
channels
are
switched in. The
volt-
ages
applied to
sockets
A
and
B
are
elec-
tronically switched.
The
frequency
in
which the
channels are
switched,
can
be
adjusted to
20 kc/s
or 500 kc/s
with switch
SK 11, located
on
aprinted-wiring board
at the
right-hand
side of the
unit.
"ALTER-
channels A and
B
are
alternately
dis-
NATE"
played.
Switching
occurs
during the
fl yback of
the time
-base voltage.
"ADDED" the
voltages at the
output
of both
ampli-
fiers
Aand Bare
added.
Dependent
on
the
position of the
polarity
switches, the
sum or the
difference
of
the
input
signals
is
applied to the
Y
-amplifier of the
basic
oscilloscope.
"EXT. The
channels are
switched
with a voltage,
CHOPPED
the
frequency of
which is
equal
to
that of
BU3" the
voltage
applied to
socket
"EXT.
CHOPPED".
TRIGG
A The
trigger
signal is
equal
to the
voltage
applied to
socket
A.
B
The
trigger
signal
is
equal to the voltage
applied to socket
B.
When
the
MODE
selector
is
in
position
"ADDED",
the
"TRIGG."
switch is out
of action.
In that case the
trigger signal is
taken from the
output
amplifier.
AC
-DC Via
this switch, the
input socket
is con -
switch nected to
the
V/cm switch.
In
the
DC-
(SK3;
SK9)
position,
the entire
input
signal
is fed to
the
V/cm
switch; in
the
AC
-position, the
DC
-component is blocked.

14
Push-button By depressing
this
button
the input
circuit
CHECK
is interrupted
and the
amplifier
input
is
ZERO earthed, so that the zero
level
can be
(SKl; SK7)
checked.
Double With this
double
knob
the
deflection
knob V/cm coefficient of
the
amplifier can
be adjus-
(R3; RS)
ted.
The deflection co-efficients are calibrated when
the
continuous
control
is turned fully
clockwise
(position
CAL.).
Polarity switch SK2 & SK8
SHIFT knob Rl & R7
GAIN control
R4
&
R6
(screw
-driver
adjustment)
DC
BAL. control R2 & R8 (screw
-driver
adjustment)
"NORM." :
a positive
-going
input
signal
causes an
upward
deflection on
the screen.
"INVERT.":
a positive
-going
input signal causes
a
downward defection on
the
screen.
With this
knob the trace
can
be shifted
in Y
-direction.
The
working -direction of
this
SHIFT
knob is depen-
dent
o~n
the
position
of the polarity switch.
The deflection coefficient of
the
amplifier
can
be
checked by
applying
the calibration voltage of
the
basic
oscilloscope to the input socket.
If the
deflection
coefficient does not
correspond to the
indicated value, it
can
be corrected by adjusting
the
GAIN control. In this
case the continuous V/cm con-
trol
should be turned
fully
clockwise (CAL.).
The DC -balance of
the
amplifier can
be adjusted with
this control.
For
this, remove the input
signal
and adjust the time -
base
generator
to its
fre-running position
(TRIGG.
MODE
to
position
AUT., or STAB. fully
clockwise).
Adjust the
DC
BAL. in such
way
that
the line
on
the
screen does
not move
when rotating
the continuous
V/cm
control.

15
Applications
A. AMPLITUDE MEASUREMENTS
When measuring the amplitude
of
a
signal,
use is made
of
the
calibrated deflection coefficients
of
the
Y
-de-
fl ection system (SK4; SK10).
Intermediate,
non -calibrated deflection coefficients
can
be obtained by
operating
R3 and
R5.
With the aid
of
the
controls of
the
basic oscilloscope
.and the
plug-in
unit, make a triggered display visible.
Check
the
zero
level
by means
of button CHECK
~
VLcm
ZERO
(SK1; SK7).
(When
the
trigger
-mode
switch is
in the
AUT. position,
the
time -base line will
remain
visible
during depression of push-button CHECK
ZER®.
When a different
position is
used, the time -base
generator
should
be adjusted to its free
-running posi-
tion
by
means of the
STAB. control).
The amplitude
of
the
total signal
is
then equal
to the
product
of deflection coefficient
and the
vertical
de-
fl ection in cm.
Amplitude:
0.5 V/cm x
3.4
cm =
1.7 V.
When only
the
AC -voltage should be measured, the
DC -component
can
be
removed from the
signal
with
the aid of the AC -DC
switch.
If measurements have
been
carried out via
measuring
probe
PM 9331 A/10, the
deflection
coefficient
of
the
V/cm
switch
should
be multiplied by a
factor 10.
'The accuracy
of
the
measurement can be increased by
precisely adjusting the
deflection coefficient with the
GAIN control in the relevant
position of
the V/cm
knob.
For
this, the
calibration voltage
of
the basic oscillo-
scope can be used.
B. DIFFERENTIAL MEASUREMENTS
With these measurements, use
is
made
of
the
common
mode
rejection of the amplifiers
in position ADDED.
When
the
polarity switches are set to opposite
posi-
tions, two
common
mode
signals on sockets A and B
will undergo a
very
slight
amplification with respect
to two
signals in
anti
-phase.
The signals on
sockets A and B should not exceed a
value corresponding to a trace
height of IO cm.
This common
mode
rejection
can
be adjusted to
maxi-
mum by
adjusting
the
amplifiers in such a way that
their
amplifications
for
the
signal
to be
measured are
exactly identical.
3.4cm
0-niveau

16
Channel A
~~
PEM
2900
Channel B
For this, simultaneously apply one of the signals to
sockets
A
and
B.
Adjust the
GAIN
control in
such a
way that a minimum trace height is obtained
on the
screen.
After this, the common mode
rejection will meet
the
value mentioned
in
the
technical data.
C.
PHASE MEASUREMENTS
If
the
phase difference
between
two
signals is to
be
measured,
the phase equality
of both
amplifiers
of
the
PM 3342 is used.
It is
recommended to set the
MODE selector
to
posi-
tion
ALTERNATE. With low
repetion
frequencies
of the time -base
generator, this working mode results
in
a
fl ickering display;
in
these
cases
the
CHOPPED
position
should be
used.
A high chopper frequency may lead to
mutual
influence
of the two
signals;
therefore,
it is recommended to set
the frequency
switch
to the
20 kc/s position.
The
signals are applied to socket
A or B respectively.
Make a
triggered display visible with the
controls of
the
basic
oscilloscope and the
PM 3342.
Both traces should be
adjusted exactly
symmetrical
with respect to the centre
horizontal
graticule
line.
The
phase difference
can
be read
directly in degrees by
adjusting
knob
TIME/cm (step- and continuous
control
of the
basic
oscilloscope)
in such a way that one period
of the
signal
to be measured
corresponds
to
a whole
number
of centimetres
on
the
screen.
D.
SINGLE TIME -BASE
If
the
signal to be measured requires the use
of
the
single -sweep
display of
the
basic oscilloscope, the
MODE switch of
the
PM 3342 should be set to
position
CHOPPED.
Selection of the
switching
frequency depends
on
the
time
coefficient of the X -deflection.
V/cm,
of
both channels: identical
Polarity
of channel A: INVERT.
Polarity
of Chanel B: NORMAL
MODE in position: ADDED
Generally, the highest
chopper
frequency
will
be used;
for
the
lower time -base speeds
however,
alsothe lowest
chopper frequency can
be selected.
Set the
controls in
the
TIME BASE A frame to the
desired positions.
When the time -base
generator
is adjusted to
its
free -
running position (STAB.
control
to
REPET),
it
will
start
immediately after depressing push-button RESET.
When the
STAB. control
is
in
the
trigger position,
the time -base
generator will start
on
the fi rst
trigger
pulse,
after depressing
the
RESET button.
During
the time
between depression of the
RESET
knob and
starting of
the time -base
generator,
the
lamp in the
RE5ET
knob
will
light up.
PEM 2899
1 period = 9 cm
phase
coefficient =
40°/cm
phase angle
cp = 40°/cm x 1.6
cm = 64°

17
SERVICE NOTES
Block
diagram
Fig. 3 shows that each channel has
independent control
for:
input coupling, attenuation, shift,
balance and
polarity. The
output
of each channel is
controlled by a
multivibrator-driven
electronic
switch,
which feeds
the
common amplifier.
Operation
of
this multivibrator
in
turn
is controlled by the MODE switch
SKS. The
MODE
switch can
either
hold
the
multivibrator in
one
of three states
or
select
one
of
three
operating
modes
for
the
blocking oscillator
which drives the multivibra-
tor.
It
will
also bee seen that
internal
trigger signals can
be derived from one
of
three sources: channel A,
channel
B
or
the common amplifier
output. The
latter
is automatically
selected
via SKS
and the relay, when
the added mode
is
used.
In
this way,
triggering
on the
desired
signal
is possible and triggering on
the
chopper
is impossible.
Display
MODE switch
SKS.
In position A
as
well
as in
position B,
the multivibrator
is held in the stable state that allows
the
signal coming
from the selected channel
to
pass through
its electronic
switch
to the
common amplifier.
In the
ADDED
position, the multivibrator is
held
in
such a
state
that both electronic
switches pass
their
signals
to the
common amplifier
where they are added.
In the CHOPPED position
the
blocking oscillator
is
free -running either at 1 MHz or
at
40 kHz, depending
on
the
position of SKll
(inside the apparatus). Pulses
from
the
blocking oscillator
drive the multivibrator,
which supplies anti -phase square -waves at 500 kHz or
20 kHz
to the
electronic
switches. Thus:
fi
rst the
signal
from
one
channel will
pass to the
common amplifier,

19
But
Channel
AC
®Ac
DC
V
~cm
SK3
(steps)
SKG
o-
~~
Stepped
Atten
SK9
o-
Bu3
Channel
BQ ~'
"Gate'~pulse
from
time base
8u2
Ext.Copped
O ~
0
R8
1
M
Hz
40 kHz
Blocking
Osc
TS
502
SK 10
Stepped
Atten
dd
Check
Zero
SK1
SK7
D.C.
Bal
Cath.
Foll.
8201-6202
V/ c m Gain shift
(cont)
R2
Cath. Foll
B 301 8302
Amplifier
TS 201
-T520G
R3 i p R1
-{ J -
R4
-6.3V
~ SK 5
11
Bu•y
Fig. 3. Block diagram
(detailed)
SK 5
Amplifier
TS 301
TS 304
®
Norrcal
Invert.
SK2
moo--~
•
~~ l l
SK8
~-o
El Switch
T 5
206
TS209
RS
0
R7
R6
El
Switch
TS306 TS309
Channel A
o r
Channel B o
SK
6
Final A m
pl.
TSG01
TSG09
~~1 Bu•y
0
0 0
24V
~r ~
~ SK 5
o
Multi vibr.
TS 503 TS
504
#z
Trigg. Ampl.
TS G02 IS 609
17
Bu -y
RE 601
--~+-►16 Bu•y
—O I
►32
Bu•y
o f
o ~
-24V
~
SK 5
O
O ~
~---~
-z4 v
~ SK
5
0
D SPLAY MODE
►
Z -Mod. A
9 Bu -y
B o
0
Chopped
SK
5
Alternate
a
Addedo p
Extchopped
o b
24V
0
p SK
5
0
PEM 2897

22
1 2 3 4 5
6 7 0 1 2 3 4 5
6 7 8 1
2
3
4
5 6 7 8 1
2 3 4 5
6 7
0
1 2 3
4 5
6 7
8 1
Input
channel A
Input
channel B
Time -base
sweeps
I
2
3
L
Output
Vertical
amplifier
Fig. 4. Typical waveforms
II
II Iff 1Y
2 3 L 5
TY
then that from
the
other. In
this way, the spot will fol-
low
apart
of
each signal in turn as shown in Fig. 4
and
as it will not
be the same part
each
sweep, the persis-
tance of vision
(and sometimes that of the CRT) will
create the
illusion of
two complete waveforms on
the
screen, as shown
in Fig. 5. To prevent hazing as
the
spot moves from one trace to
the
other, blanking
pulses,
derived from
the
blocking oscillator,
are fed to
the
CRT via 9 BU -Y.
II I IY I II II
I
3
L 5 6
Fig. S.
Display
~~
3 L 5 6 7
_~
I II
~-
5 6
7 0
I
_~
PEM
2898
In
the EXT. CHOPPED
position, operation
is the
same as for CHOPPED,
except that now the
blocking
oscillator will
not
be free
-running
but has
to be
trig-
gered, via BU2, by an
external signal.
In the ALTERNATE
position, the blocking oscillator
is
triggered during the
fl y
-back of
the time -base. Thus
the spot traces out fi rst
one
signal
and then the other.

23
Vertical am~li Fier
1.
Pre
-amplifier
channel A
(Fig.
21)
The incoming signal is fed directly or via a capacitor
depending on
the
position of switch
SK3 (AC -DC),
to
a
10
-step
attenuator, which reduces
the
signal
amplitu-
de by
afactor 1, 2,
5, 10 etc. up to 1000, as selected with
switch SK4 (V/cm).
Cathode
-follower B201
provides an
impedance trans-
formation to drive the following transistor amplifier.
As
the cathode
-follower is subject
to some DC -drift, a
second cathode
follower B202 is symmetrically
con
netted to it to minimise drift. Furthermore, provision
is made to balance the
amplifier
by varying
the grid
potential
of B202 at R321 "COARSE DC -BALANCE"
and
R2 "DC-BAL".
When
properly
adjusted, no
signal will
be present
across R3 (CONTINUOUS
CONTROL) if
the grid
circuit of B201 is connected to earth with switch SK1
("CHECK ZERO").
Clamping diodes
GR202
and GR203 prevent the tran-
sistor amplifier (TS201-TS202) driving signal
from
becoming intolerably high in either
the positive
or
the
negative
direction. Protecting
diode GR201, which is
normally forward biased, p~ events the
maximum
(negative) grid -to
-cathode voltage from being
exceeded,
because
if such a signal is present, protecting
diode
GR201 will
be
reversely biased.
The cathode voltage
will then
be determined by the
—150
Volts
supply
and
the voltage -drop across R206 due to the
cathode
cur-
rent.
To
complete the temperature -compensation,
the
cathode circuit
of B202 is likewise
provided
with
diode
GR206
of
the same type. Diode
GR204
prevents high
voltages from
being
applied to
TS202.
The second stage is formed by
emitter
-followers TS201
and
TS202.
They
offer a low
impedance
signal
source
for
the next stage and
for
the
trigger -amplifier, which
receives
its
signals via
R232
and
R237.
From conti-
nuous
control
R3, the
signal
is routed to the third stage,
TS203-TS204.
This stage can be regarded as an asymmetrically driven
long
tailed
-pair amplifier.
The output
of this
stage
consists of
two
equal,
but
opposite,
signals. GAIN control R4
influences the
negative
feedback
and
consequently
the amplification
factor.
R235 and C211
provide
a correction
to
obtain
optimum
step -response.
Shift
controls Y -SHIFT (R1 -R1')
and the polarity
switch SK2
are inserted
between
the third and fourth
stage. The connections from the third stage to SK2 and
from SK2
to the fourth stage are effected by
means
of
a
300 Ohm ribbon
line,
which is
terminated by R249 and
the series -connection of R254
-R256. The
power
is
supplied at the junction of R254
-R256. In this
way,
the
total dynamic
resistance at the collectors of
TS203
and
TS204 amounts
to
75
Ohms.
The
fourth
stage consists of two
cascode
amplifiers
(TS206-TS208 and TS207-TS209)
which are push-pull
connected. Transistors TS206
and TS207 act as
current
sources
to the
low
-ohmic inputs of TS208
and TS209
respectively. Thus hardly any signal
voltage
will
be
present at the emmitters of TS208
and TS209, so
it
is
possible to carry out
the
electronic
switching
at this
point.
If
the voltage at
R508
becomes more
positive
than
the
emitter
voltage,
switching
diodes GR209
and GR211
are blocked,
thus allowing normal
operation
of
the
cascode-amplifiers. If
the voltage at R508 is
decreased
below the
potential
at the bases of
TS208 and TS209,
the transistors
are
fully
blocked and diodes GR208
and
GR212
likewise. So no signals
will
pass
and
channel
A
is
cut
off.
In
the
emitter
circuit
of
TS206 and TS207,
R263 and
C217 provide low frequency
compensation;
C218
improves the step -function
response.
2. Pre -amplifier channel B (Fig. 21)
This pre
-amplifier
is identical
to that
of channel A.
The
switching
voltage of channel B however,
is
counter -
phased. Thus the diodes
GR309-GR311 are
conductive
when GR209-GR211
are blocked and
vice versa .As a
result, the
signal of channel
A is
displayed when
channel B
is blocked and vice versa.
3. Output
amplifier
(Fig. 21)
The
driving
signals
of
the output amplifier
are devel-
oped across R402 and 8406. Emitter
-followers TS401-
TS402
offer
these signals with a low
source
impedance
to cascode-amplifiers
TS403-TS406 and
TS404-TS407
The amplified signals are
fi nally
routed to
the output
stage
consisting of emitter
followers
TS408-TS409
which make them available to
the
vertical
amplifier of
the basic oscilloscope via terminals 1
and 17 of BU -Y.
When
the
MODE -switch SKS is in
position ADDED,
diodes GR209-GR211-GR309-GR311
are
blocked
simultaneously
so that both channels
are switched in
and a combined signal is
applied to the output ampli-
fi er. To maintain
the same voltage
-level
at R404, R401
is
connected
in parallel.
The two cascode-amplifiers are connected in push-pull
arrangement
with
a
high
common
resistance at the
emitter
side of TS403-TS404 thus forming
one
differen-
tial amplifier. C422, C401
and R413 improve
the step-
functionresponse.

24
Switching
control
circuits
1. Blocking oscillator (Fig. 20)
1f
SKS is
in
the
CHOPPED position, switch SKS IA is
open,
so that the
potential
at the base
of TS502 is
de-
termined, by voltage
-divider R 504-506.
It is adjusted
so that
the
blocking
oscillator
becomse astable,
oper-
ating
at a
repetition rate of 40 kHz
or 1 MHz depending
on
the
position of SK11).
In all
other
positions
of
SKS
,switch SKS lA is
closed,
thus setting
the base
to
approximately emitter -potential.
TS502
is almost
cut-off
but
it
will
operate
when
a nega-
tive pulse
arrives
at the base
from
terminal
4 of
S2
(transformer T501).
If SKS is
in
the
ALTERNATE position, C500 and
R511 differentiate
anegative-going
pulse,
which arrives
at
terminal 11 BU -Y and which has the same
duration
as the
GATE
pulse
of
the
basic oscilloscope. The
posi-
tive
-going
spike resulting
from the trailing edge, is
passed by diode
GR507
to
emitter
-follower TS501,
which injects it into winding SS
of transformer T501.
The
inverted pulse is applied to the base
of TS502,
which triggers
the
blocking
oscillator
to
deliver
one
pulse,
after
which the
oscillator returns
to
its quiescent
state.
If SKS is in the EXT.
CHOPPED position,
the
signal
entering
at
BU2 is differentiated by C500 and
R511
and
triggers the
blocking oscillator as mentioned
under
ALTERNATE.
Every
time
the blocking
oscillator operates, a
pulse
appears at
winding S1 of transformer T501.
It
is
routed
to
terminal 9BU-Y
to
momentarily blank the display
on the sereen. To ensure that the
blanking pulses
reach
the
CRT at the moment that the
switching
pulse (delayed
by the
vertical amplifier)
reaches the
Y -deflection plates, a 120 nanosecond delay -line is
fi
tted
in
the
main
frame.
Resistor
R503
(470 S2)
ter-
minates this delay line to avoid
reflections.
2. Multivibrator (Fig. 20)
The
bi-stable
multivibrator TS503-TS504
is locked
in
postition: TS503
cut-off. TS504
conductive,
when
MODE
selector
SKS is in
position A.
As a result, the
electronic switch of channel A is closed and that of
channel B
is
open.
When SKS is
in position B, TS504 is
blocked and the
signal of
channel B
is displayed.
When SKS is in the
ADDED position,
both transistors
are blocked
and both electrcnic switches are therefore
closed.
When SKS is in
the
CHOPPED, ALTER-
NATE ar EXT. CHOPPED positions,
the bi-stable
multivibrator switches at half the rate of the
blocking
oscillator.
It may be observed
that switching diodes GR501
and
GR502 are conductive when
their appertaining tran-
sistors
are
conductive. They
then offer
a
low
ohmic
path
to
an incoming negative
switching
pulse. The
transistor will
be blocked and also the diode
which will
then turn into ahigh-ohmic impedance.

25
Trigger amplifier
O
The
trigger
amplifier (Fig.
19) consists
of four
push-pull
stages which
are
directly coupled to each
other.
The fi
rst
three
stages
are
long-tailed
pair
amplifiers: the fourth
stage is connected
as an emitter -follower output
—stage.
The balance
of
the
amplifier is
adjusted at the
fi
rst stage
by R605; the quiescent DC
-level of
the output is ad-
justed
by changing the value
of
R623.
The
output of
the
trigger amplifier
is connected to the
trigger
amplifier
of the
main
frame via contacts
of
relay
RE601.
When MODE selector SKS is in
the
ADDED
position,
the relay is energised and the output
of
the
trigger
amplifier is disconnected. The
main
frame
trigger am-
plifier is then connected to the output
of
the
vertical
amplifier.

26
Checking and adjusting
A. GENERAL INFORMATION
The
tolerances
mentioned are
factory
tolerances; they
apply when
the apparatus is readjusted completely.
They may differ from the data
given
in II.
A summary of
the
adjusting elements, their
nomencla-
ture and
location has been given in V.
With the aid
of
these data, it is possible to
carry
out
all
the adjustments of the
dual
trace unit PM 3342 and
to
check the proper working of the plug-in unit.
For this,
the unit should be inserted into the
Y -plug-in
compartment
of
a
correctly
adjusted
basic
oscilloscope
PM 3330.
Some
of the adjusting elements are on the right-hand
side
of
the unit and
are
not
directly
accessible. When
these
elements
must be adjusted, the unit should be
connected to the
basic
oscilloscope
via
the rigid
exten-
sion plug (code
number
4822 263
70009).
For a
complete
adjustment of the instrument the se-
quence
as described in this
chapter
is to
be
preferred.
R 313
Fig. 6. Right-hand view
B.
D.C.
BALANCE
This adjustment should be carried out
when
the unit
has
obtained
its operating
temperature, i.e.
approxi-
mately
15
minutes after switching -on.
Set the
knobs
of the basic oscilloscope to the
following
positions:
"TRIGG. MODE": "AUT."
"TRIGG.
SOURCE":"[NT."
"TIME/cm": "2 msec./cm"
"X -DEFLECTION": "TIME BASE A"
1. Channel A
R213 (Fig. 6)
Set
"MODE"
(SKS) to "A" and
turn "D.C. BAL."
(R2)
to
its
mid
-position.
During
this adjustment,
keep
the
time -base
line
on
the
screen with "SHIFT" (R1).
— Adjust the coarse
control "D.C. BAL." (R213)
so,
that the time -base line
hardly moves when "V/cm"
(R3) is turned
fully
clockwise
or anti
-clockwise.
— With the
fi
ne
control "D.C. BAL." (R2), adjust
for
a
stationary
display.
I
R
213
TS
608
TS 609
TS
602
TS 603
15