Heathkit IO-4550 User manual

° _‘-HEATHKIT
MANUAL
for the
10 MHz, DUAL-TRACE
OSCILLOSCOPE
Model 10-4550
OPERATION 595-1850-01
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Price $2.00
Heathkit® Manual
for the
10 MHz, DUAL-TRACE
OSCILLOSCOPE
Model 10-4550
OPERATION 595-1850-01
@
Copyright
©
1976
Heath Company
SS HEATH COMPANY All Rights Reserved
BENTON HARBOR, MICHIGAN 49022 Printed in the United States of America

Page 2
INTRODUCTION
SPECIFICATIONS
OPERATION
TABLE OF CONTENTS
oy by icbat at ait tt Md, ee, ops 3 IDENTIFICATION CHARTS
VIEWS oie ob ee ees Ss
ee ee ee a ee ee 8
TROUBLE LOCATOR
bs fat take aN tan haat te: So dar cae 15 CHARTS .........
4 CIRCUIT BOARD X-RAY
(In the “Illustration Booklet’)
(In the “Illustration Booklet”’)
(In the “Illustration Booklet”)
Inside front cover
Inside rear cover

(——3¢ Feo eee
INTRODUCTION
This Oscilloscope is a portable, triggered-sweep, dual-trace,
DC-to-10 MHz, laboratory-grade instrument. Outstanding
features such as the fast vertical rise time, good trace
brightness, and the high input sensitivity make the
Oscilloscope ideal for the wide range of measurements
typically encountered in electronics, development
laboratories, and scientific research. In addition, the rugged
construction and dependable operation make it a versatile
tool for either the hobbyist or the service technician.
Each of the two identical vertical input channels provides a
maximum signal sensitivity of 10 millivolts/centimeter.
Their attenuator networks can be switched through 11
calibrated ranges to set the deflection factor from 10
millivolts/centimeter to 20 volts/ centimeter.
Several modes of signal display are selected by each
channel's position control and the Time Base switch. Either
or both channels can be displayed as a function of time or as
a function of each other. At slower sweep speeds, the
vertical channel signals are alternately displayed at a 200
kHz (approximately) rate (chopped mode) so both signals
appear as a function of the same time base. For faster sweep
speeds, both signals are displayed alternately (alternate
mode) on successive sweeps. During X-Y operation, the
Channel Y1 (X) circuits provide horizontal (X axis)
deflection and the Channel Y2 (Y) circuits provide vertical
(Y axis) deflection.
Calibrated time-base ranges from .2 seconds/centimeter to .2
microseconds/centimeter are readily switched in a 1-, 2-,
5-step sequence. A control on the Time Base switch provides
Page 3
variable sweep speeds between switch positions. Any sweep
speed can be expanded 5 times when the X5 control is
pulled out, giving a maximum sweep speed of 40
nanoseconds/centimeter.
The Trigger Select switch and Level control allow the time
base to be precisely triggered at any point along the positive
or negative slope of the trigger signal. Various trigger signals
can be selected. These include a sample of Channel Y1 or
Channel Y2 input signals, an externally applied trigger
signal, or a sample of the line voltage. The Trigger Mode
switch controls the trigger input bandpass. A special TV
position cuts off unwanted high frequency signals. This is
especially useful when you want to trigger on TV vertical
frame signals.
A calibrated 1-volt peak-to-peak square wave signal is
provided through a front panel connector, allowing easy
probe compensation, vertical amplifier calibration, and
comparison.
Front panel display controls include Intensity, Focus, and
Vertical and Horizontal position. An additional control,
accessible through the rear panel, adjusts Astigmatism. An
internal switch is used to match the regulated power supply
to conventional line voltages from 105 volts to 260 volts
AC.
Thus, this Oscilloscope combines the most desirable features
required for precise measurement and display, while its
solid-state circuitry provides excellent sensitivity, stability,
and versatility.

Page 4
SPECIFICATIONS
VERTICAL
Deflection Factor:
Sensitivity: 2. “nis Ste Fe: eee we oh eS SX 10 mV/cm to 20 V/cm.
Attenuator 2.6 mi cent eed aee dou wes 11 steps in 1-2-5 sequence.
WariaDle: a0 ce ue. ide oe ree do wR Continuous between steps to approximately 60 V/cm. 0
ACCUTACY © x. 3) She Boe. eS ewe ee Se ee wi Ww PR Within 3% (10°C to 40°C), referred to 0.2 V/cm.
Vertical Response:
DE: Coupling: sa diS Ss news ie Ac ste Pe. eS DC to 10 MHz (—3 dB) at 6 cm.
AG Coupling: 5:0 668%. oe eee Sw Se Se we iw 2Hz to 10 MHz (—3 dB) at 6 cm.
Rise Time va od Se Be ee Pe ws 35 ns.
Overshoot 2... 2 2 eee ee tt te Less than 5%.
Vertical Input:
impedance: 2s es wd ee we BRE oy re 1 MQ shunted by 38 pF.
Maximum Input . 2... 2 ee ee et ee ee 400 V peak combined AC and DC.
Connector ......-.-. ee Pe @ BNC.
Vertical
Modes:
Sine
.
+e
eee
eee
tte
tes
oh
bed
Y1
or
Y2
selected
by
POSITION
control.
;
Dual
.--
eee
ete
et
tees
hak
ote
a2
Chopped
(200
kHz)
or
alternate
automatically
selected
by
oO.
TIME/CM switch.

Page 5
Gegurmarrrire
e
HORIZONTAL "
Time Base:
Ramp: sacs tcvles aa et vee BE ~ Se 0.2 s/cm to 200 ns/cm.
POSItIONS <é. cd ee ee Sp ey OO es SHH SS 19 steps in 1-2-5 sequence.
Variable sx © se eee SA Bee we eR EE RS Continuous between ranges to approximately 0.6 s/cm.
ACCUTECY: cance Sw eee eB Re ae Within 3% (20°C to 30°C) 5% (10°C to 40°C). Referenced
to 1 ms/cm at 25°C.
Magnifier «66s te ee ee ee Ske eee ees X5 (adds additional 2% to sweep accuracy.)
External:
Sensitivity 2 26-32. ew oe elo ore SS wee @ 0.1 V/cm (approximately).
lmipedance: £05 2b BS www RR ee YR 100 kQ (approximately).
‘Ss
Polarity
.
wos
efi
oter
te
pal
seg
ia
Sew
ter
BS
eS
Positive
input
causes
right-hand
deflection.
Frequency Response .......-.+.22-2- DC to 1 MHz (—3 dB).
Connector 246s sa Sew Saw SE we BNC.
TRIGGER
Internal:
Automatic ....... ot ah be ton tee Gh tn BS Ob Adjustable over 10 divisions.
NOPD) ooo. sick Rt EE BS ee wee Adjustable over 10 divisions.
Slope Selection .......-2.0 002 eeeae +or—.

DC: auto DC to 20 MHz DC to 20 MHz
norm | DC to 20 MHz DC to 20 MHz
auto 20 Hz to 20 MHz 20 Hz to 20 MHz
norm | 20Hz to 20 MHz 20 Hz to 20 MHz
: auto 20 Hz to 1 kHz 15 Hz to 2 kHz
norm | 20 Hz to 1 kHz 15 Hz to 2 kHz
External:
AUtOMatie:
nie
es
oo
eb
ee
we
ea
we
Adjustable
over
0.8
V.
Normal
ee
ee
ee
ee
ee
eee
eee
Adjustable
over
0.8
V.
SoBe) We ee week ne SL NSE ere Ue, ett ar ca +or—-.
DC to 20 MHz DC to 20 MHz
DC to 20 MHz DC to 20 MHz
20 Hz to 20 MHz 20 Hz to 20 MHz
20 Hz to 20 MHz 20 Hz to 20 MHz
20 Hz to 1 kHz 20 Hz to 2 kHz
20 Hz to 1 kHz 20 Hz to 2 kHz
Impedance ..- +--+ eee ee eee eee eee 1 MQ shunted by 40 pF.
Connector
2. ee
ee
tet
ee
eet
ee
te
BNC

Gg
umarexire
Page
7
X-Y
ViGnanmel: a sess we ve i ks rere 6s ae we es See a te ae Same as Vertical.
M Channel 2 se 2s okt eee aS KR Se Bs Same as Vertical, except response is limited to 1 MHz.
Phase Shift) a:0a.6°-4 ace ace Sore BS oe are es Less than 8° at 100 kHz.
GENERAL
CRT:
TYPES ab oer ee ee as wt BE aS ee FR ey 5” round, mono accelerator.
Acceleration Potential ..........-. bed hi Se 1.8 kV regulated.
©
Phosphor ....... by ewe he se ol BOS P—31.
Graticul@. sos. 3% ee RE ea we ee aw we ee 8 by 10 cm.
Power:
Voltage
Range...
1...
eee
ee
ee
ee
es
105
to
130
VAC/210
to
260
VAC
switch
selected,
70
watts
at 120 VAC (240 VAC).
Internal Supplies .. 1... 1.2 2 ee ee ee eee Fully regulated.
Operating Temperature Range ....... +222 ee 10°C to 40°C.
Dimensions: ..5. 6 oe eee es a Sw a we Height: 6.937 in. (17.6 cm).
Width: 12.875 in. (32. 7 cm).
Length: 19.25 in. (48.9), without handle.
Length: 21.5 in. (54.6 cm), with handle.
Weiglit: 206 sm 3 6 coe eA oe OS ee ee me 22 Ibs. (10 kg).

Page
8
[eeeg=emarererrs]
OPERATION
This section of the Manual explains the function of each
control, switch, and connector; gives a preset for each
control and switch; describes how to correlate between
time/cm and frequency; and provides operational examples.
ALTERNATE
PRIMARY
VOLTAGES
In
the
United
States
120
VAC
line
voltage
is
most
often
used,
while
in
other
countries
240
VAC
line
voltage
is
more
common.
If
your
line
voltage
is
consistently
below
115
volts
(or
below
230
volts
if
you
intend
to
Operate
the
Oscilloscope
on
240
volts),
perform
the
following
steps.
Otherwise,
proceed
to
“Control
Functions.”
NOTE:
Electrical
regulations
in
some
areas
require
a
special
line
cord
and/or
plug
for
240-volt
operation.
Replace
them
if
necessary.
(_)
Remove
the
top
and
bottom
covers
of
the
Oscilloscope.
If
your
line
voltage
is
consistently
below
115
(or
230)
volts:
(_) Shift the NOR/LOW switch to the LOW
position. (See Figure 23 in the “‘I\lustration
Booklet”).
\f you intend to operate your Oscilloscope on 240 volts:
position. This switch is located on top of the
rear subchassis, between the CRT and power
transformer.
(_) Shift the 120/240 slide switch to the 240 re)
(_ ) Remove the 1-ampere slow-blow fuse and install
the 1/2-ampere slow-blow fuse supplied with
this instrument. The fuseholder is located on the
bottom side of the rear subpanel.
( ) Reinstall the top and bottom covers. Be sure the cover
edges fit into the side rail grooves before you tighten
the two thumbscrews.
CONTROL FUNCTIONS
NOTE:
Some
illustrations
that
are
too
large
for
the
Operation
Manual
are
included
in
a
separate
“‘Illustration
Booklet.”
Use
these
large
illustrations
when
a
step
refers
to
the
“Illustration
Booklet.”
Refer to Figure 1 (in the ‘Illustration Booklet’) for the
location and explanation of the front panel controls and
switches,

1.
INTENSITY
FOCUS
HORIZ POS
TRIG MODE
TIME/CM
VARIABLE-
Pull for X5
TRIG
LEVEL
Y1:
POSITION
‘“VOLTS/CM
VARIABLE
INPUT switch
Y2:
POSITION
VOLTS/CM
VARIABLE
INPUT switch
Page 9
PRESETTING CONTROLS
Set the front pane! controls and switches as follows:
Fully counterclockwise (PWR OFF)
Center of rotation
Center of rotation
AC
-ImS
Fully clockwise (CAL) and pushed
in (X1)
Y1, + (plus)
Center of rotation and pushed
in (AUTO)
Center of rotation
50 mV
Fully clockwise (CAL)
GND
Fully counterclockwise (OFF)
50 mV
Fully clockwise (CAL)
GND
The following procedure will prepare the Oscilloscope for
operation in any mode, and may be used at any time to
check the basic instrument operation.
2. Connect the line cord to an AC power source.
CAUTION: Do not permit a bright dot to remain on the
face of the cathode ray tube for a prolonged period of time;
a dot will burn the phosphors and leave a permanent image
in the face of the CRT.
3. Turn the INTENSITY control clockwise 1/3 of its
rotation.
4. Allow a minute or two for the instrument to warm up.
5. Slowly adjust the Y1 POSITION control and the
HORIZ POS control to center the trace on the screen.
6. Adjust the INTENSITY control to obtain a trace just
bright enough for your room lighting conditions.
7. Adjust the FOCUS control for the finest and sharpest
trace.
8. Adjust the HORIZ POS control so the trace starts at
the left edge of the graticule.
Your Oscilloscope is now prepared for operation in the
modes described in the “Operational Examples” section.

Page 10
DC BALANCE (DC BAL)
The highly sensitive vertical amplifier input circuits in this
Oscilloscope, as in other sensitive equipment, may exhibit an
occasional unbalance caused by aging components and
temperature effects. Even though the DC BAL (balance)
control is not considered to be an operating control, you
should make it a habit to check the DC balance periodically
and readjust it when necessary. You will need a small
screwdriver to make this adjustment through the small hole
in the front panel.
To check the DC balance of either channel, set the input
switch (AC-GND-DC) to ground (GND) and obtain a trace
on the CRT. Turn the VOLTS/CM VARIABLE gain control
from fully clockwise to fully counterclockwise. If the trace
moves vertically, readjust the DC balance as follows:
1. Turn the VOLTS/CM switch to the 10 mV
Position.
(8x Fs News Se
fully Y
2. Turn the VARIABLE gain control
counterclockwise.
3. Center the trace on the screen.
4. Turn the VARIABLE gain control
clockwise to the CAL position.
fully
5. Adjust the DC BAL control to return the trace
to the centerline.
6. Repeat steps 2 through 5 until the trace does
not move when the VARIABLE gain control is
turned.
NOTE: If the trace does not move as the VARIABLE gain
control is turned, but moves when the VOLTS/CM switch is
changed, perform the “Vertical Amplifier Balance’ on Page
27.
NORMAL
OPERATING
CHARACTERISTICS
The following information is provided to help answer
Possible questions you may have about the operation of
your Oscilloscope.
Several minutes may be required for the trace to
stabilize when the Oscilloscope is first turned on,
especially on the more sensitive voltage ranges.
Random noise on the input signal may cause false
triggering, especially on the most sensitive voltage
ranges.
A baseline will automatically appear after a short 6
pause when the trigger LEVEL control is pushed in to
the AUTO position or when the input signal is
disconnected when automatic triggering is used.
In the EXT horizontal mode, the horizontal position of the
trace may change with different. horizontal
resistance.
driving
USING A 10 MILLIVOLT OSCILLOSCOPE
When you use an Oscilloscope as sensitive as this, you must
use special care to make reliable measurements. Keep the
following points in mind when you measure very low level
signals.
Placement of the ground clip may be critical if the
signal
source
ground
carries
an
appreciable
current.
Voltage
differences
of
several
millivolts
from
one
side
of
a
chassis
or
ground
foil
to
the
other
are
common.
Place
the
ground
clip
at
the
point
that
gives
the
least
error.
This
is
usually
nearest
the
signal
source.
You
may
have
to
move
the
ground
clip
when
you
measure
different
points.
Stray 60 Hz pickup may be hard to eliminate,
especially in high impedance circuits. Be sure to use
shielded test cables. Shield the signal source if
necessary.
Wideband measurements in the millivolt region are
more difficult because of the inherent noise (shot
noise and thermal noise) generated by electronic
components. This may appear as a widening of the
baseline or the baseline appearing out of focus. Noise
on the baseline that appears as “hash” or “‘spikes’’
may be’ caused by the electromagnetic pickup of
man-made noise such as ignition noise, appliance
noise, etc. Noise of any kind may cause erratic
triggering.

GaegetmarrrrriTe
Page
11
Ce
OPERATIONAL EXAMPLES
This section of the Manual gives several examples of how to
use the Oscilloscope in its different modes of operation.
These examples will help you become familiar with the
controls, especially the sweep and triggering controls, and ©
with dual-trace operation.
EXAMPLE 1
Triggering the Sweep on the + or — Slope of a Waveform
Signal source: Sine wave generator capable of a 1 kHz, 1 volt
rms signal.
Be sure all controls and switches are in the positions
described in “Presetting Controls’’ (Page 9). Do not change
any of these settings unless you are directed to do so ina
step. Connect the Y1 vertical input cable to the sine-wave
generator output. Place the Y1 INPUT switch (AC-GND-DC)
in the AC position and set the VOLTS/CM switch to 500
mV. Be sure the VARIABLE control is fully clockwise.
Turn the TIME/CM switch to the .1 mS position. (The
VARIABLE—X5 control should be fully clockwise and
pushed in.)
Turn the LEVEL control to the 12 o’clock position and be
sure it is pushed in. Then turn it slightly each way from the
center and observe the leading (left-hand) edge of the
waveform. Note that the LEVEL control sets the point on
the waveform when the sweep starts. See Figure 2.
TRIGGER
START
POINT
es
ZONE
e4cRGEe as
i a=
a aa a
Change the TRIG switch to Y1 minus (—) and note that
triggering now starts on the downward or negative slope of
the waveform as in Figure 3. Vary the LEVEL control to
move the starting point up or down on the slope.
Figure 2
Return the TRIG switch to the Y1 plus (+) position and the
LEVEL control to center and pulled out. Then set the
INPUT switch to its center (GND) position and the trace
will disappear.
Figure 3
The waveform will appear only when the INPUT switch is in
either the AC or DC position. Leave the Y1 INPUT switch in
the AC position. A baseline will automatically appear when
the INPUT switch is in the GND position and the LEVEL
control is pushed in.
Now, assume that you want to examine the “spike” on
waveform A of Figure 4. First, adjust the LEVEL control so
the sweep starts just before the spike, as in B of Figure 4.
Then decrease the time required for one complete sweep by
changing the position of the TIME/CM and/or the X5
switch. The X5 expands the sweep around the center two
centimeters. The spike is now spread across a large area of
the screen for closer observation, as in C of Figure 4.
Figure 4
Read the TIME/CM and X5 switch settings to determine the
duration of the spike. This feature is also useful to observe
distortion in circuits using square wave signals.
The X5 function causes the beam to theoretically travel five
times further. Thus, to sweep across one centimeter, the
trace must now travel this distance in 1/5 the time specified
by the TIME/CM switch. When the X5 magnifier is used
(pulled out), the true sweep speed is found as follows:
OR Time/cm (x) .2 True time/cm = Timelem
Example: Time/cm switch setting = 2 mS/cm
X5 switch pulled out.
True time/cm = ae = 0.4 mS/cm

Page
12
EE
EXAMPLE 2
Normal or Automatic Triggering
The AUTO mode (automatic triggering) provides a base or
reference line without the presence of a vertical input signal.
This line is used as a reference point, especially for DC
measurements.
With the controls and switches set as they were at the
conclusion of Example 1, and with a waveform of the 1 kHz
sine wave signal on the CRT, push in the LEVEL control to
the AUTO position. The trace will appear as one complete
cycle.
Make sure the TIME/CM switch is in the .1 mS position and
the VARIABLE control is fully clockwise and pushed in.
Figure 5
Slowly increase your signal generator frequency to 2 kHz
and note that the display on the CRT remains locked in. At
2 kHz, two complete cycles of the input signal will be
displayed as in Figure 5.
XAMPLE 3
Trace Operation
source: Sine wave — square wave generator capable of
e. simultaneous, sine wave and square wave output, 1
‘ne wave signal to the Y1 INPUT and the
| to the Y2 INPUT.
| Y2 VOLTS/CM switches at 1V and
AC; then set the following switches
1, plus (+)
Cc
enter
of
rotation
and
shed in (AUTO)
mS
Adjust the Y1 and Y2 POSITION controls so the two
waveforms are separated on the CRT. The display will be
similar to that shown in Figure 6.
tH |
LN | | TANT
APNOACNC
| | RYT TT RY
| ft | |
aa ey
mms en a
ia a
le Gr ee ees
a es
NOTE: Either channel can be turned off by turning the
respective POSITION control fully counterclockwise to the
detent (OFF) position.
Figure 6
Turn the LEVEL control so triggering occurs at the peak of
the sine wave as in Figure 7. Note that this is at the
midpoint of the positive portion of the square wave.
ea pt aA Sd
NER ANEEE.
Figure 7
Return the LEVEL control to the center of rotation and the
waveforms will again appear in their generated phase
relationship.
EXAMPLE 4
X-Y Mode Operation
With the TIME/CM switch in the X-Y position, and the
TRIG in Y2, Y¥2 (Y) signals produce vertical deflection while
Y1 (X) signals produce horizontal deflection. In the X-Y
mode, the Y1 (X) controls and switches affect the
horizontal display. Adjust the HORIZ POS control so the
Y1 (X) POSITION control will move the spot off the screen
in both directions.
Trapezoidal and Lissajous patterns that are useful in
studying modulation characteristics, and frequency and
phase comparisons, result from applying separate signals to
the Y1 (X) and Y2 (Y) inputs in the X-Y mode.
ry )
i

([—— Se FSV So
HORIZONTAL
af LINE
“O,
B.,
W.
VERTICAL
TANGENT LINE
Figure 8
Typical Lissajous patterns are shown in Figure 8. The
Pattern depends upon the relative amplitudes, frequencies,
and phase of the two voltages. The frequency ratio can be
figured from the formula:
fx Th (f)
x= Ty
Where f, is the unknown frequency, Th is the number of
loops which touch the horizontal tangent line; Tv is the
number of loops which touch the vertical tangent line; f is
the known frequency.
When using Lissajous figures, it is good practice to have the
figure rotating slowly rather than remain stationary. This
eliminates the possibility of an error in counting the tangent
points. If the pattern is stationary, a double image may be
formed. In such cases, the end of the trace should be
counted as one-half a tangent point rather than a full point.
This condition may occur when neither frequency can be
varied.
Example 5
Phase Measurements (X-Y Function)
It is sometimes necessary to determine the phase
relationship between two AC voltages of the same
frequency. This can be accomplished quite easily by
applying one of the voltages to the horizontal input and the
other voltage to the vertical input. The phase relationship
can be estimated from Figure 9.
Page 13
ao ge ee
0°,
360°
30°,
330°
60°,
300°
90°,
270°
120°,
240°
150°,
210°
180°
Figure
9
NOTE: For proper displays, the horizontal amplifier gain
must be set to equal the vertical amplifier gain.
To calculate the phase relationship, use the -following
formula:
A
Sin 6 -B , where @ is the phase angle.
As shown in Figure 10, distance A is measured from the X
axis to the intercept point of the trace and the Y axis. The
distance to B represents the height of the pattern above the
X axis. The axes of the ellipse must pass through the point
0.
Y AXIS
Figure 10

Page 14
Example 6
TIME/CM-To-Frequency Correlation
Eleven vertical and nine horizontal lines on the graticule,
spaced 1 centimeter apart, permit the measurement of
displayed waveforms. The short markers on the centerlines
are spaced 2 millimeters apart. Use the following formula to
determine the frequency of a waveform displayed on the
CRT.
TIME/CM switch*
setting in seconds
per cm.
1
- MAGNIFIER
Centimeters for 1 Period of
X cycle of unknown = unknown
frequency frequency.
pare sie
and, Period ~ Frequency
EXAMPLE: If one cycle of a waveform measures 2 cm on
the graticule, with the TIME/CM switch at 1 mS and the X5
switch pulled out, then —
sey]
7
1
001°"
X
5
X
2
=
.0004,
and
0004
= 2500 Hz.
NOTES:
“The VARIABLE —X5 control must be fully clockwise to
use the calibrated TIME/CM switch settings in this formula.
**1 millisecond = .001 second; 1 microsecond = .000001
second.
When the X5 switch is pulled out, the sweep travels 5 times
further. (theoretically), which makes the sweep time shorten
by a factor of 5.
q
)

Page 15
THEORY OF OPERATION
The dual-trace capability of this Oscilloscope allows two
different signals to be displayed on a conventional CRT
(cathode ray tube) that has only one set of vertical
deflection plates. Two identical vertical preamplifier circuits,
a switching circuit, and a vertical deflection amplifier make
this possible. Each vertical preamplifier circuit attenuates its
input signal by a known factor, amplifies it to a usable level,
and provides the necessary positioning bias. The switching
circuit (a diode-type switch), which is automatically
controlled by the display control circuit, alternately allows
the output signals from the two preamplifier circuits to pass
to the vertical deflection amplifier. The vertical signal, a
composite of both input signals, is amplified further by the
vertical deflection amplifier before it is applied to the
vertical deflection plates of the CRT. The signal at the
vertical deflection plates, which produces the display on the
CRT screen, thus represents both input signals as one
“time-shared”’ signal.
The horizontal portion of the trace displayed on the CRT
screen is produced by the sweep and trigger circuits in
conjunction with the horizontal deflection amplifier. The
sweep circuit produces the linear signal (ramp) used to
sweep the electron beam across the CRT screen from left to
right at a constant rate. This circuit is switch controlled (by
the TIME/CM switch) to provide nineteen accurate sweep
rates needed to view and measure almost all input signals.
This circuit must be triggered either by a portion of one of
the vertical input signals, by an external signal, or by a
Portion of the line frequency signal.
In the absence of a trigger signal, an automatic baseline
circuit causes the sweep circuits to operate while in the
automatic mode. This ensures that, even though no signal is
applied, a reference baseline (trace) will appear on the CRT
screen. The sweep signal is coupled to the horizontal
deflection amplifier where it is amplified before being
applied to the horizontal deflection plates of the CRT.
Other circuits within the horizontal amplifier also provide
the necessary positioning bias.
At the end of each horizontal sweep, the blanking circuits
(which are triggered by the sweep circuits) turn the trace off
(blank it). This prevents a line (retrace) from being displayed
as the electron beam returns to the left side of the CRT
screen to start a new trace.
Regulated power supply circuits ensure overall accuracy as
well as excellent control of the electron beam size and
intensity.

Page
16
:
[eg
=emarersrr’]
CIRCUIT DESCRIPTION
Refer to the Block Diagram and the Schematic Diagram (in
the “Illustration Booklet”) as you read this “Circuit
Description.”
Components are numbered in the following groups:
1-99 Parts on the chassis.
100-199 Parts on the vertical circuit board.
200-299 Parts on the horizontal circuit board.
300-399 Parts on the low voltage circuit board.
400-499 Parts on the high voltage circuit board.
VERTICAL
The vertical preamplifier consists of two identical circuits:
One for Channel Y1 and the other for Channel Y2.
Components in the Channel Y1 vertical preamplifier circuit
are designated by a —1 suffix, while those in the Channel Y2
vertical preamplifier are designated by a —2 suffix. (For
example: A Channel Y1 divider resistor is R101-1, while the
same divider resistor in Channel Y2 is R101-2). Components
without a suffix do not relate to a specific channel. Since
both channels are identical, only Channel Y1 is described in
this ‘Circuit Description.”
INPUT CIRCUIT
When
Y1
input
switch
SW1
(AC-GND-DC)
is
in
the
DC
position,
a
signal
applied
to
the
Y1
input
connector
is
coupled
to
the
input
attenuator.
When
the
Y1
input
switch
is in the AC position, the signal is coupled through capacitor
C1, which passes only AC signals. This permits an AC signal
superimposed on a DC potential to be seen without the DC
component being displayed. The GND position of this
switch disconnects the input signal and grounds the
attenuator input. This allows the trace to be adjusted to a
zero reference without disconnecting the test leads from the
circuit under test.
Because the second (Q109-1/Q110-1) and vertical deflection
amplifiers (Q111-Q114), which will be discussed later,
operate at a fixed gain, any signal applied to them must be
within a usable range (approximately 80 mV/cm).
Therefore, the primary purpose of the vertical input circuits
is to reduce or increase the input signal by a known factor to
this usable level.

GagumAcrriTe?
The vertical input circuit basically consists of an attenuator,
an input follower, and a switched-gain amplifier. These
circuits function together, through the VOLTS/CM switch,
to provide the total desired attenuation or gain. The
attenuator obtains its four attenuation factors (1, 10, 100,
and 1000) from four divider networks (resistors R101-1 thru
R106-1, and capacitors C101-1, C103-1, C104-1, C106-1,
C107-1, and C109-1). At DC and low AC frequencies, the
resistive dividers reduce the input signal level; while at higher
frequencies, attenuation is determined by _ the
resistor-capacitor (RC) networks.
Cops in the Atfenuator netunel
Trimmer capacitors C101-1, C104-1, and C107-1 are used to
adjust the capacitor division ratio to match the resistor ratio.
Trimmer capacitors C102-1, C105-1, C108-1, and C111-1
are adjusted during calibration to make the input
capacitance of the Oscilloscope equal on all positions of the
VOLTS/CM switch. This is essential when an attenuation
probe (usually X10) is used.
i tupet Follawe. |
The input follower circuit consists of a FET
(field-effect-transistor) source follower, DC current source,
and an impedance translator. The attenuated input signal is
coupled through resistors R108-1 and R109-1, and capacitor
C112-1 to the gate of FET source follower, Q101-1.
Capacitor C112-1 forms a high frequency path around
R109-1 for improved frequency response. Input protection
is provided by two FET’s (D101-1 and D102-1) wired as
reverse biased diodes. They are connected to the plus (+),
and minus (—) 15-volt supplies. Thus, if the input signal,
after the input attenuator, exceeds 15 volts the FET’s
become forward biased and clamp the signal to within a
diode drop of 15 volts. This prevents damage to Q101-1 if
the VOLTS/CM switch is in a low range, and a high potential
is applied to the input.
'
Transistor Q101-1 provides the high input impedance
necessary to prevent attenuator loading and a low output
impedance to drive emitter follower transistors Q103-1 and
Q104-1. To compensate for the DC voltage present at the
source of Q101-1 when no signal is applied, FET Q102-1
forms a DC current source. DC BAL control R85 is adjusted
so that the current supplied is sufficient to produce a zero
output at the source of Q101-1 for a zero input at the gate
of Q101-1. The circuit formed by diodes 0103-1 and
D104-1, and transistors Q103-1 and Q104-1 acts as an
impedance translator, It reduces the output impedance of
the input follower to approximately 50 ohms. The output of
the input follower is coupled to the switched-gain amplifier.
Page 17
This switched-gain amplifier is formed by transistors Q105-1
and Q106-1 to provide a double-ended output from a
single-ended input signal. A relatively constant current is
supplied through resistor R119-1 to the amplifier, so that an
increase in current through Q105-1 will cause a
corresponding decrease in current through Q106-1. Thus, as
Q105-1 amplifies the input signal, Q106-1 produces an equal
but opposite signal. This creates a push-pull effect on the
signal, which is amplified in the following stages to drive the
vertical deflection plates of the CRT. Front panel
VARIABLE control R128-1 adjusts the gain of the amplifier
when it is turned from its detented CAL (fully clockwise)
Position.
Two switch-selected RC networks reduce the gain of this
switched-gain amplifier from 8 to 4 and 1.6. Table I shows
how the VOLTS/CM switch selects the various attenuation
factors and gains of the switched-gain amplifier to provide
the desired total gain. STEP BALANCE control R124-1
adjusts the collector currents of Q105-1 and Q106-1 so that
the CRT trace does not shift when the gain (VOLTS/CM
switch) is switched.
TABLE I
VOLTS/CM] ATTENUATION | AMPLIFIER] TOTAL
FACTOR GAIN
FACTOR
-
=
4
8
6
4
8
1.6
4
8
6
4
8
To illustrate how the attenuator and switched-gain amplifier
work together for the proper gain, assume the VOLTS/CM
switch is in the 10mV position and a 10mV signal is applied
to the input. Since the total gain factor is 8, the input signal
is amplified by a factor of eight before it is coupled to
follower
Q107-1/0108-1.
An
BOmV
signal
at
the
follower
i se a_ 1 cm deflection in ow assume
the VOLTS/CM switch is in the 500mV position and a
500mV signal is applied to the input. The total gain factor is
now .16. Multiplying the input signal by the total gain factor
results in an 80mV signal to the follower (S00mV x .16 =
80mV), again causing a 1 cm deflection on the CRT screen.

Page 18
Differential emitter follower Q107-1/108-1 serves as a buffer
between the switched-gain amplifier and second amplifier. It
also provides vertical trace positioning. Y1 Position control
R138-1 controls trace position by shifting the emitter
current between the two emitter circuits. From the follower,
the signal is coupled to the trigger amplifier and second
amplifier. The trigger amplifier will be described after the
“Vertical Deflection” section.
The second amplifier is a differential amplifier with a gain of
approximately 10. Its output is direct-coupled to the diode
bridge. CAL control R164-1 adjusts the gain of this
amplifier and the overall calibration of the vertical circuit.
DIODE SWITCH
Both preamplifier circuits (channels Y1 and Y2) share the
vertical deflection amplifier. This is accomplished with two
high-speed diode switch networks (D107-1 thru D110-1 and
0107-2 thru D110-2) that are actuated by the display
control circuit. When one diode switch is turned on, the
other is turned off so that only one signal can be coupled to
the vertical deflection amplifier. Two-channel operation is
accomplished by turning each diode switch network on and
off at a rapid rate or on alternate display sweeps. Control of
the diode switch will be described in a later section.
VERTICAL DEFLECTION
From the diode switch, the input signal is direct-coupled to
the vertical deflection amplifier. This amplifier (comprising
transistors Q111, Q112, Q113, and Q114) is wired in a
(xe Fe VS
differential cascade configuration, with a gain of
approximately 20. Capacitor C126 across the emitters of
Q111 and Q112 provides high-frequency square wave
compensation. Ferrite beads FB101 and FB102 in
common-base amplifier Q113/Q114 prevent oscillations in
the amplifier. Circuit loading is supplied by resistors R174
and R176, while inductors L101 and L102 serve as peaking
coils. The output of this amplifier is coupled to the vertical
deflection plates of the CRT for beam control. Vertical
beam deflection requires between 12 and 15 volts/cm,
depending on individual CRT charactistics. The vertical CAL
control, R164-1, in the vertical input circuit adjusts overall
vertical gain to match the CRT deflection characteristics.
TRIGGER AMPLIFIER
A differential amplifier and follower comprise the trigger
amplifier circuit. Its output is used to supply a trigger signal
to the horizontal time base, trigger, and sweep circuits. In
addition, the Channel Y1 trigger signal can be switched to
the horizontal deflection circuit for X-Y operation.
A portion of the input signal is coupled from follower
Q107-1/Q108-1 to the input of the differential amplifier in
the trigger amplifier circuit. Emitter follower Q117-1
couples the trigger signal from the inverting leg (Q115-1) of
the differential amplifier (Q115-1/Q116-1) to the horizontal
time base, trigger, and sweep circuits. Transistor Q118-1 is a
temperature-compensated constant current source for this
circuit. The Zero control (R149-1) in the emitter leg adjusts
the current so that the output of the follower will be zero
with no signal to the trigger amplifier. Thus, the circuit
performs as a differential to single-ended converter.
@