Heath Zenith SO-4226 User manual

HEATH
l /L L
25 MHz OSCILLOSCOPE
Model SO-4226
595-3896
HEATH
COMPANY
Copyright
©
1987
Heath Company
BENTON HARBOR, MICHIGAN 49022 All Rights Reserved

Page 2
Precautions for Use
Inspect the shipping carton for serious ship-
ping damage. If you notice damage, notify the
carrier immediately.
Before you apply power to the Oscilloscope,
make certain that the voltage selector plug on
the rear panel has been inserted with the
arrow marking in the direction of the proper
line voltage. Also check the fuse to be sure
it is of the proper rating.
Do not leave a bright beam on the CRT screen
for long periods. This can cause permanent
damage to the screen.
This instrument is convection-cooled. Always
be sure the cooling vents are not blocked
when you are operating it.
To insure stable operation over long periods
of time, do not subject the Oscilloscope to vi-
bration, direct sunlight, extreme temperature
variations, high humidity, dust, or elec-
tromagnetic fields.

Page 3
Table of Contents
INTRODUCTION
.
..ottt
einee
s
4
Horizontal/Time
Base
.
...................
18
CalIbTator /o PP Rieniniis s i s v vavauns 19
BPECIFICATIONS
.
vovve
e
deaneti
Vo
Hlnmmne
5
CRT-Cant8l
.
o0l
%
vs
iy
s
vunnnn
19
Power: Supply: . . . . .inadalantlad i D s 19
OPERATION ;5505455 sammmnanns s § s ¢ ¥ prone 9
Controls
and
Connectors
..................
9
MAINTENANCE
&
ADJUSTMENTS
..........
20
Preliminary
Operation
...................
11
General
Maintenance
....................
20
Triggering
the
Sweep
...................
11
Adjustment
and
Calibration
..............
20
X-Y
Display
Operation
..................
12
Power
Supply
Adjustments
............
20
Voltage
Measurements
.
..................
12
CRT
Circuit
Adjustments
..............
21
Dual*Trace-Display
«¥%.
#8000
T
o
v
Vertical
Axis
Adjustments
.............
21
Synchronizing
TV
Signals
Horizontal
Axis
Adjustments
...........
23
Addition and Subtraction Operation ....... 12
SCHEMATICS .. ..ttt 24
APPLICATIONS!
ccoesioisstimmnssssssas
13
Vertical
Amplifier
Schematic,
AC
Voltage
and
Frequency
Part
1
somonsssss
6000
ivvsasmmisistonsse
o o
o
o
o
25
Measurements .. ......oouerereenennn.n 13 Vertical Amplifier Schematic,
-
DC
Voltage
Measurement
................
13
Part
120
spouns
65
05
55
58§
&
Do
&
5
5
9
26
AM
Modulation
Measurement
............
14
Horizontal/Time
Base
Schematic,
Dual
Trace
Applications
.
.
.
.
.ovweisa
s
wns
14
PETE
1
ovnvasen
s
00
5% 55
85
8
50
BSQEEREESE
3
8
27
Comparison of Levels «:::vvsmonmemiansens 14 Horizontal/Time Base Schematic,
Checking
Stereo
Systems
................
14
=75
2
R
28
SErvicing
TV
Sets
zisussssnssosmenutasss
14
Power
Supply
and
CAL
Schematic
........
29
Composite
Video
Analysis
...............
15
HV
Supply
and
CRT
Frequency
Measurement
With
Circuit
Schematici
.
.::
s
uv
s
v
o
s
30
X-Y Method . ....... ... .. .l 15
Phase
Measurement
.....................
15
REPLACEMENT
PARTS
LIST
...............
31
GIRCUIT
DESCRIPTION
‘ccusiie
s
6
6 o
5
w
sszovscsinse
»
17
CUSTOMER
SERVICE
INFORMATION
.......
32
General sy vowonaupmmenn s 5§ ¢ o 9 s 17
Veitical,
AMPIfier-
cuwammsss
s
s
5
5
o
awemeaes
17
WARRANTY
.o
s
34

Page 4
INTRODUCTION
The vertical amplifiers on this dual-trace 25 MHz
Oscilloscope have a calibrated sensitivity of 1
mV/division, a flat frequency response, and a
smooth rolloff above 25 MHz. Maximum sweep
speed is 20 ns/division. The 8 X 10 cm rectangular-
type CRT with internal graticule gives the Oscillo-
scope a good look, while it is rugged enough for use
in developmental work, on production lines, in
. maintenance, and in servicing. This scope also has
the following features:
®
6 0
06060
0
0
0
Wide bandwidth and high sensitivity.
High stability with low drift.
Video delay line.
A high-sensitivity X-Y mode.
A Z-axis modulation input.
A TV video sync filter.
A trigger level lock function.
Variable trigger hold-off.
A single sweep function to display single-shot
waveforms.
A high brightness CRT.

Page 5
SPECIFICATIONS
VERTICAL DEFLECTION
Deflection Factor ..............c.oouviiinnn.
Magnification c.is « + cosmssin s s & smmsawmprs & x s
Bandwidth (at =3dB) .iowsidn’s 23 mamienmness5s s
Rise Time . .......ooiuiiiiiiiiiiiiinnann,
OVErSHOOE cv.ussemsuiss s & susrarsramsamens 5,5 sistosonsmossgsss s & & o «
Input Impedance. . . sseuevsin s v s vvsvmmnss o ss
Maximu;x; V In;ut ............................
Operating Modes . covinnsiiisssssmmnirisine
Chop Frequency ..............oeeeeuuennnnn.
Channel Separation .........................
CH1 Signal Oulput , ..o s s s smmamen s s o s s
CH2: Polarity’ s« 5 » s 5 5 ¢ sogesmmms b+ 45 4
HORIZONTAL DEFLECTION
Sweep IMode) v s » cevitisuis 5 5 = s § 5 » 596
SWeeD TilDE s 5 v aemuiens § § & JEEmes § 5 4 59
Magnification ............... ... ool
Sweep Time ACCUTACY . ..« .vvvvvnnennennnnn.
Trigger Holdoff Timei. b « « » wemmsrsmons & s « wa s
Linearitye woss s ¢ 3 snomuens 5 5 § o uesme ¥ 55 ¢ 0
5 mV to 5 V/DIV = 3%; 10 steps in 1-2-5 sequence
with variable control.
5 times (1 mV/DIV to 1 V/DIV at X5 MAG).
DC: DCto 25 MHz (DCto 15 MHz at X 5 MAG).
AC: 10 Hz to 25 MHz (10 Hz to 15 MHz at x5
MAG).
Approximately 14 ns (approximately 23 ns at
x5 MAG).
Less than 3%.
1MQ shunted by 25 + 3 pF.
400V p-p, or 200 V (DC + AC peak).
CH1, CH2, DUAL, and ADD.
Approximately 250 kHz.
Over 60 dB at 50 kHz, 30 dB at 25 MHz.
Approximately 100 mV/DIV. -
Waveform inversion; variation less than 1 DIV.
AUTO, NORMAL and SINGLE.
0.2 ps to 0.5 s/DIV; 20 steps in 1-2-5 sequence with
variable control and X-Y mode.
X 10 (provides sweep time of 20 ns/DIV).
3% (6% at x 10 MAG).
Adjustable to longer than 5 times sweep length in
0.2 us/DIV to 1 ms/DIV ranges.
3% (6% at x 10 MAG).

Page 6
X-Y Operation ...,
SensttiVILY, . wcssssins « 5 o sammomes 5 96 & & 3 semEEE
Frequency ReSpONSe « ;s oo owuvvissss v sswmnsvs
TRIGGER
INTENSITY MODULATION (Z-axis)
Input Voltage ...............ccooiiinii. ...
Inputi Resistants s s s & sommamns 6 5 5 § sussemnsg
Maximum Input ............................
Frequency Range ...........................
Mode selected with SEC/DIV switch:
CH1: X-axis.
CH2: Y-axis.
Same as CH1 vertical axis.
DCto 1 MHz (-3 dB).
CH1, CH2, LINE and EXT.
INT: 0.5DIV from DC to 15 MHz.
1.5 DIV from DC to 25 MHz.
EXT: 50mV p-p from DC to 15 MHz.
100 mV p-p from DC to 25 MHz.
AC, HF REJ, TV, and DC.
HF REJ: Attenuates signal components .above 50
kHz.
+0r =,
AUTO, NORM, and SINGLE.
Preset level from 50 Hz to 25 MHz.
Input Impedance: 1 MQ, 30 pF.
Maximum Input: 100 V (DC + AC peak).
3 V p-p or higher (Bright at negative-going input).
Approximately 5 kQ.
50 V p-p (DC + AC peak).
DC to 5 MHz.

Page 7
GENERAL
CRT Accelerating Voltage .................... Approximately 2 kV.
Calibration
Voltage
. :
.cuusmiizin
¢
»
o
o
sionaavsiaiia
o
s
«
2V
p-p
*+
2%,
1
kHz
square
wave
(positive-going).
Power
Requirements
..............
...
117
V;
50/60
Hz;
approximately
35
VA.
FUBE .« covvmmmnn » ¢ 5 v vammsen 5 o 5 % % s s 2 5 1Afor117 V.
DIMensions
cwsms
s
s
555
amameis
55
¢
»
¢
e
o
12.4"”
W
X
6.5
H
x
17.1"
D
(315
X
165
X
435
mm).
WEIBHE . . oonoliiths o o o o bdeiutiie 8's 3 5 3 samaoni i s 5 Approximately 15.4 Ibs (7 kg).
e —— < ———
The Heath Company reserves the right to discon-
tinue products and to change specifications at any
time without incurring any obligations to incorpo-
rate new features in products previously sold.

Page 8
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25 MHz osciloscope
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Figure 2

Page 9
OPERATION
CONTROLS AND CONNECTORS
Refer to Figure 1 and Figure 2 as you read the follow-
ing numbered paragraphs.
1.
2.
10.
POWER — Turns the instrument on and off.
CAL 2V terminal — Provides a 1 kHz square
wave output. It is useful for checking
amplifier gain, waveform compensation of
probes, etc.
INTENSITY — Adjusts the beam’s brightness.
FOCUS — Adjusts the clarity of the beam.
TRACE ROTATION — Used to offset the ef-
fect of the earth’s magnetic field on the trace
line.
SCALE ILLUM — Adjusts the scale back-
ground light.
POSITION/PULL ADD — Positions the CH1
display vertically. In the X-Y mode, using
EXT IN, this control positions the CH1 Y-axis.
When pulled out (ADD mode), the CH1 and
CH2 input signals are algebraically added.
AC-GND-DC (CH1 and CH2) —
AC: The signal is capacitively coupled to
the vertical amplifier and any DC
component is blocked. The low-fre-
quency limit (-3dB) is about 10 Hz.
GND: Grounds the amplifier input and
opens the input circuit.
DC: All components of the input signal
are coupled to the vertical amplifier.
CH1 (X) connector — BNC connector con-
nects the input signal to channel 1.
VOLTS/DIV switch (CH1 and CH2) — Selects
deflection factors from 5 mV/DIV to 5 V/DIV
in 10 steps.
11.
12
13.
14.
15.
16.
VARIABLE VOLTS/DIV control (CH1 and
CH2) — Variable controls for vertical attenua-
tion. Provides continuously variable deflec-
tion factors (sensitivity) between the steps of
the VOLTS/DIV switch. Normally they are set
fully clockwise (CAL). When they are pulled
out, the sensitivity is magnified by a factor
of 5.
VERT MODE selector —
CH1: Displays Channel 1 only.
DUAL: A dual trace display switches be-
tween CH 1 and CH2, with alter-
nate or chopped operation con-
trolled by the SEC/DIV switch.
Chopping occurs at approximately
250 kHz on the 0.5 s to 1 ms/DIV
ranges and on alternating traces on
the 0.5 ms to 0.2 ps/DIV ranges.
CH2: Displays Channel 2 only.
Ground terminal — Provides a chassis ground
that is connected to the 3-wire AC power
cord.
CH2 (Y) connector — BNC connector con-
nects the input signal to channel 2.
POSITION/PULL INVert — Positions the CH2
display vertically. In any X-Y mode, this con-
trol positions the CH2 Y-axis. When it is
pulled out, the CH2 display is inverted.
HOLDOFF — Adjusts the time between
sweeps, and is used when the time base trig-
gering must be delayed to display complex
waveforms (e.g. repetitive complex pulses).
When you turn this control clockwise, from
full counterclockwise (NORM), the holdoff
time is continuously variable from no delay
to 5 times normal sweep time. Operates only
on ranges from 0.2 ws/DIV to 1 ms/DIV.

Page 10
17,
18
19
20.
21.
22.
EXT IN — A BNC connector for external trig-
ger signals. In the X-Y mode, with the TRIG-
GER SOURCE switch at EXT, the signal ap-
plied to this connector controls the X-axis of
CH1 and/or CH2.
LEVEL — Selects the starting point voltage
on the trigger source waveform at which the
sweep is triggered. Turn the control fully
counterclockwise to FIX (NORM) for a fixed
level (0 volts).
SOURCE — Selects the triggering source sig-
nal as follows:
CH1: CH1 signal for triggering.
CH2: CH2 signal for triggering.
LINE: AC line-frequency voltage for trig-
gering.
EXT: The signal applied to the EXT IN
connector for triggering.
COUPLING — Selects the triggering mode as
follows:
AC: Trigger signals are capacitively
coupled to the trigger circuitry.
Signals below 10 Hz are at-
tenuated.
HF REJ: Attenuates triggering signals
above 50 kHz.
TV: For observing TV signals.
DC: All trigger signals are directly
coupled to the trigger circuitry.
SLOPE — Selects the triggering point on the
positive or negative portions of the trigger sig-
nal.
SEC/DIV — Selects calibrated sweep rates
from 0.5 s/DIV to 0.2 ps/DIV in 1-2-5 sequence
(20 ranges). At X-Y (fully counterclockwise),
operation is for the X-Y mode. The alternate
or chop and TV-V or TV-H operations are au-
tomatically selected by the switch.
23.
24.
25.
26.
27.
28.
29.
SWEEP MODE selector —
AUTO: For normal triggering.
Sweep free-runs in the
absence of an adequate
triggering signal.
NORMAL: For normal triggering.
No CRT display in the
absence of a triggering
signal.
Allows only one sweep
until reset. Reset the cir-
cuit by pushing this
switch. The READY
lamp indicates when the
circuit is ready to be
triggered. .
SINGLE/RESET:
POSITION — Positions the CH1 and/or CH2
trace horizontally.
VARIABLE/PULL X10 MAG — Provides con-
tinuously variable sweep rates to approxi-
mately 2.5 times the calibrated setting. At the
CAL position, the sweep rate is set by the
SEC/DIV switch. When you pull this VARI-
ABLE switch out, the sweep speed is ex-
panded 10 times.
Z AXIS INPUT connector — A BNC input
connector for intensity modulation of the CRT
trace.
OUTPUT connector — This BNC output con-
nector provides the signal from the CH1 verti-
cal preamplifier.
Fuseholder — Holds the AC line fuse. The
rating is given in the nearby table.
AC INPUT socket — Receptacle for the 3-wire
AC power cord.

PRELIMINARY OPERATION
1; Control settings:
A. POWER switch to OFF.
B. All three POSITION controls to mid-
range.
INTENSITY contrcl to midrange.
Push the sweep VARIABLE knob (25) for
normal conditions.
Push the AUTO button of SWEEP MODE
(23).
VARIABLE VOLTS/DIV (11) pushed in.
CH1 switch pushed in.
Other controls may be at any position.
Check the AC line voltage and plug in-
stallation on the rear panel.
oo
2
e
2. Connect the AC line cord between the AC
INPUT socket and an AC outlet.
3. Set the POWER Switch to ON. After about 20
seconds, a trace line will appear on the
screen. If it does not appear, adjust the IN-
TENSITY control to increase brightness to
suit your lighting conditions.
4. Adjust the FOCUS and INTENSITY controls
for a clear trace line.
5: Readjust the vertical and horizontal POSI-
TION controls to obtain the desired location.
6. Connect a 10:1 probe to the input of CH1 and
hook the tip to the CAL 2 V terminal.
2 Set the VOLTS/DIV switch of CH1 to 50 mV
and the VARIABLE knob fully clockwise. Set
the trigger SOURCE selector (19) to CH1. A
square wave covering 4 divisions will then
be displayed.
8. If the square wave has excessive rounding or
overshoot, adjust the trimmer in the probe.
9. Remove the probe from the CAL terminal and
repeat steps 6 through 8 for a second probe
at CH2. The Oscilloscope is now ready for
use.
Page 11
TRIGGERING THE SWEEP
The horizontal (time base) circuitry can operate in
three modes: AUTO, NORM, and SINGLE. In the
AUTO mode, triggering of the sweep occurs even
in the absence of an input signal. In the NORM
mode, a display occurs only when conditions estab-
lished by the triggering controls and switches are
met (as described below). The SINGLE mode is iden-
tical to the NORM mode except that only one sweep
can occur and the RESET button must be pushed
after each sweep to enable the next sweep. The
READY lamp indicates that the circuit is reset.
Triggered oscilloscopes include circuits to display
stable waveforms. The synchronizing pulse for the
triggering is derived from the vertical or a time-
related signal. It is important that the triggering be
synchronized with the vertical input. Five controls
are provided in this Oscilloscope for this purpose:
1. SOURCE Selector (19):
CH1: For internal triggering with the
CH1 input signal.
CH2: For internal triggering with the
CH2 input signal.
LINE: The AC line frequency is used for
triggering.
EXT: An external triggering signal con-
nected to the EXT IN connector is
used. This provides three benefits,
depending on operating condi-
tions:
A. Triggering is not affected by
variations of the vertical sig-
nals. For example, the trigger-
ing point normally changes
for changes in the setting of
the VOLTS/DIV switch since
the synchronizing source
voltage changes. Unless the
external trigger voltage is
changed,
triggering
is
very
stable and not dependent on
the vertical control settings.
B.
You
can
delay
the
input
signal
by
using
the
delay
function
of
a pulse generator.
C.
A
composite
or
modulated
signal
can
be
easily
triggered.

Page 12
2. COUPLING Selector (20): Selects the syn-
chronizing circuit coupling. “AC” is for AC
coupling and the DC component is blocked.
At HF RE], a low-pass filter is used to sup-
press any RF noise interference. The TV set-
ting is for TV signal triggering; selection is
made for TV-V or TV-H by the SEC/DIV
switch.
3; SLOPE Selector (21): Selects the trigger slope,
positive or negative, of the trigger signal. For
TV synchronizing, the point is set to the rise
or fall time of the pulse.
4. LEVEL Control (18): For stable triggering con-
trol over an adjustable range. The FIX
(NORM) position selects a zero voltage offset
to the trigger level.
5. HOLD-OFF Control (16): Improves triggering
for _the . display.. of irregular repetitive
waveforms. Adjust as required to delay retrig-
gering the sweep.
X-Y DISPLAY OPERATION
For the most common X-Y applications, set the SEC/
DIV switch to X-Y, the TRIGGER COUPLING switch
to DC, the TRIGGER SOURCE switch to CH1, and
PUSH the CH2 pushbutton of the VERT MODE
switch. All CH1 functions operate as a horizontal
(X-axis) amplifier with the horizontal position con-
trol, while CH2 functions as a vertical (Y-axis)
amplifier. For X-Y operation with dual Y channels,
set the TRIGGER SOURCE switch to EXT and con-
nect the X-axis signal to the EXT IN BNC connector.
Both CH1 and CH2 then display Y-axis signals.
VOLTAGE MEASUREMENTS
You can use either the CH1 or CH2 input of the Os-
cilloscope as a voltmeter to measure peak, peak-to-
peak, DC voltages, or a specific portion of a complex
waveform.
1. Set the VARIABLE control of the VOLTS/DIV
to the CAL position. Next set the VOLTS/DIV
switch for the trace amplitude to be used. Ad-
just the vertical POSITION control to set the
reference level.
2: For DC or compiex signals, first set the input
switch to GND and then adjust the vertical
POSITION control for a reference level. A
positive voltage will deflect the trace upward
and vice versa. For the voltage, multiply the
vertical (division) deflection by the setting of
the VOLTS/DIV switch. NOTE: When a 10:1
probe is used, the waveform display is only
1/10 of the actual voltage being measured.
DUAL TRACE DISPLAY
The MODE selector is set to DUAL. In this operating
mode, procedures given above are the same.
SYNCHRONIZING TV SIGNALS
Set the Trigger COUPLING selector (20) to TV. TV
frame and line triggering is automatically selected
by the SEC/DIV switch. That is, frame is selected
on the .5 s to the .1 ms positions, and line is selected
from the 50 ps to the .2 us positions.
ADDITION AND SUBTRACTION OPERATION
When the CH1 POSITION knob is pulled (ADD
mode), the display will be the algebraically added
waveforms of CH1 and CH2. The subtracted
waveform is displayed when the CH2 vertical POSI-
TION knob is pulied for INVERT.

Page 13
APPLICATIONS
This Oscilloscope has full capability for single trace
operation on each channel. For simplicity, only CH1
operation will be referred to below.
Control settings:
AC-GND-DC switch ............ AC or DC
VERT MODE selector ............... CH1
COUPLING selector ............ AC or DC
SOURCE selector ................... CH1
Probe cable ........ Connect to CH1 input
Connect the probe tip to the point of measurement
and the ground clip to the chassis or grounded area.
NOTE: The input impedance of this instrument is
1 MQ, with 25 pF in shunt. With a 10:1 attenuation
probe, multiply the voltage reading by 10. The peak-
to-peak voltage at the point of measurement should
not exceed 400 V.
AC VOLTAGE AND FREQUENCY
MEASUREMENTS
Initially, set the VARIABLE knobs of the VOLTS/DIV
and SEC/DIV switches (11) and (25) to the CAL posi-
tions. An example is shown in Figure 3.
From Figure 3:
P-P voltage ........... 0.5/div x 4 = 2V
Peak voltage .......... 0.5/div x 2 = 1V
Effective voltage ........ Peak V + V2 =
0.707V
Frequency, Hz ........ 1/Time (sec), where
Time = No. of DIVs
per cycle x value of
SEC/DIV
For the waveform in Figure 3, frequency =
= —— =250kHz.
1 1
1ps X4 (div) 4ps
e aav —
VOLTS/DIV .
SEC/DIV
. at0.5Vv
.. atlus
DC VOLTAGE MEASUREMENT
Set the AC-GND-DC switch to GND. Push the
SWEEP MODE switch (23) to AUTO and then posi-
tion the trace on one of the scale lines for a 0 V
reference.
Set the AC-GND-DC switch to DC. The trace will
shift upward for + or downward for — polarity.
DC voltage = Shift in divisions x VOLTS/DIV
setting.

Page 14
AM MODULATION MEASUREMENT
There are several methods of measuring AM mod-
ulation, but here the envelope method is shown.
This method is applicable only if the carrier fre-
quency is within the bandwidth of this instrument.
Figure 4 shows the display of a modulated wave.
DUAL TRACE APPLICATIONS
For this application, set the VERT MODE selector
to DUAL. Signals at Channel 1 and 2 will be dis-
played simultaneously. The two signals can then be
compared with respect to level, waveform, phase,
etc.
SOURCE
OUTPUT
COMPARISON OF LEVELS
An example of interconnections is shown in Figure
5 for the output/input level comparison of an
amplifier.
Set the displays of CH1 and CH2 to be superimposed
using the POSITION controls. The gain in the
amplifier will be the difference in settings of the re-
spective VOLTS/DIV switches. When the signals
cannot be matched, even if the VARIABLE controls
are adjusted, the difference is due to distortion in
the amplifier. In this case, set the VERT MODE selec-
tor to ADD and pull the POSITION knob of CH2
to view only the distortion; the trace will be a
straight line when distortion is absent.
CHECKING STEREO SYSTEMS
Stereo "audio systems have two ~ symmetrical
amplifier circuits. Using the dual trace feature, it is
possible to compare and check the operation in each
circuit. Location of any defective portion is thus sim-
plified.
SERVICING TV SETS
In this application, a triggered oscilloscope is indis-
pensable. This instrument can synchronize to either
the TV-V (Frame) or TV-H (Line) of the video signal
to display the blanking pedestal, VITS, or vertical/
horizontal synchronizing pulses.
OSCILLOSCOPE
CH1
INPUT
o AMP
[
R LOAD Y
% o
I—g CH2
[
Figure 5

COMPOSITE VIDEO ANALYSIS
The most important waveforms in TV servicing are
the composite signals consisting of the video, blank-
ing pedestal and sync pulses. Figures 6 and 7 show
composite signals synchronized with horizontal
synchronizing and vertical blanking pulses.
BURST VIDEO
" HORIZONTAL HORIZONTAL
SYNC PULSE BLANKING PULSE
Figure 6
VIDEO
VERTICAL VERTICAL
SYNC PULSE BLANKING
Figure 7
Page 15
FREQUENCY MEASUREMENT WITH
X-Y METHOD
Set the SEC/DIV switch and trigger switches for X-Y
operation. Connect a standard frequency signal to
CH1 and the unknown signal to CH2. Then CH1 is
the X-axis and CH2 the Y-axis. The display will be
the lissajous figure, examples of which are shown
in Figure 8.
(AR
e
@
rassss
swomn
JOORN
Figure 8
;| (6 PHASES SHOWN)
PHASE MEASUREMENT
Using the X-Y function, connect the two input sig-
nals to the CH1 and CH2 connectors. The phase is
calculated with the relation shown in Figure 9.
SINE 0
n
8
A
PHASE ANGLE
©
n
Figure 9

CHI CHI
(x)
ATT
CH2
() @ ATT
EXT IN@——— GENERATOR
CAL O=— CALIBRATOR
CHI ouTPUT
__________ a
VERTICAL DEFLECTION UNIT |
|
| CRT 6*
CH1 | - 7
PRE AMP — VERTICAL | {—=
CHI | lswreHng] OUTPUT AMP | -
TRIG AMP T
|
( MODE) |
SELECT |
CH2
|
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TRIG
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CH2 SELECT I
TRIG AMP [ | t
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s esatemsss s s e e i iy
HORIZONTAL DEFLECTION UNIT E 2Ky
INT TRIG. (X AXIS) |
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TRIGGER SWEEP HORIZONTAL | HORIZONTAL[——— 1 {conTROL[™] supeLy )
GENERATOR SWITCHING QUTPUT AMP) | ¥ ]
I : [z axis |
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el
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_CRT
CIRCUIT
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SupPLY — Z AXIS INPUT
Figure 10 Block Diagram

Page 17
CIRCUIT DESCRIPTION
GENERAL
The block diagram of the Oscilloscope is shown in
Figure 10. Refer to it as you read the following para-
graphs.
The vertical deflection unit has independent at-
tenuator/preamplifier circuits for CH1 and CH2, a
vertical switching circuit, and a vertical output
amplifier. Each attenuator/preamplifier circuit
amplifies or attenuates its input signal, which is
then fed to the switching circuit. The trigger signals
also are picked off at this stage.
The vertical switching circuit electronically
switches the signals from the CH1 and CH2
preamplifiers and couples them to the vertical out-
put amplifier. The trigger signals are also switched
and fed to the trigger generator for internal trigger
signals.
The horizontal deflection unit has a trigger
generator, a sweep generator, a horizontal switching
circuit and a horizontal output amplifier.
The switching signal from the vertical switching cir-
cuit or EXT IN connector is amplified and shaped
to a trigger pulse signal in the trigger generator.
The sweep generator is driven by the pulses from
the trigger generator and produces a sawtooth signal
in the triggered sweep mode.
The horizontal switching circuit electronically
switches the sawtooth signals from the sweep
generator in the normal mode and from the trigger
signals (internal, line, and external) in the X-Y
mode. These signals are then coupled to the horizon-
tal output amplifier to provide the horizontal deflec-
tion.
The CRT circuit is comprised of a high voltage reg-
ulator to accelerate the electron beam, a Z-axis
amplifier to blank out the return traces, and a CRT
control circuit to adjust the trace.
The high voltage regulator provides a 2.0 kV voltage
to be applied to the CRT cathode to accelerate the
electrons. The Z-axis amplifier amplifies the un-
blanking signals received from the sweep generator
and the intensity modulating signal for application
to grid 1 of the CRT.
The CRT control circuit provides various voltages
for the electrodes so that the CRT is properly biased.
All the power supplies are regulated for stability.
VERTICAL AMPLIFIER
NOTE: Refer to the schematic diagrams on Pages 25
through 30 as you read the following paragraphs.
Each of the CH1 and CH2 attenuator circuits consists
of two attenuators. The first attenuator is for 1/1,
1/10, and 1/100, and the second attenuator provides
1/1, 1/2, 1/4 and 1/10 portions of the first attenuator
output. By switching these attenuators with the
Volts/DIV switch (S2-1/S102-1), the signal can be at-
tenuated in a range of 1/1 to 1/1000 in 10 steps. A
voltage follower circuit (Q1-Q4/Q101-Q104) is in-
serted between the first and second attenuators to
obtain a high input impedance. The second at-
tenuator provides a low-impedance output signal to
be fed to the first differential cascade amplifier (IC2/
1C102).
The first differential cascade amplifier is comprised
of an emitter-connected differential current
amplifier and a current-to-voltage converter (IC2 or
1C102). This amplifier also has the Variable circuit
(VR39/VR139) for continuously-variable adjustment
of the deflection factor between the steps of the
Volts/DIV switch, and the X5MAG switch (S2-2/
$102-2) for magnifying the vertical sensitivity by 5
times.
The second differential cascade amplifier (Q5,6.7,8/
Q105, 106, 107 — 110) amplifies the output from the
first amplifiers to a level that is sufficient to drive
the vertical switching circuit. The Q109. Q110 por-
tion of the amplifier is used with the INV switch
to invert the polarity of the CH2 signal.

Page 18
The output signal of the second amplifier is fed di-
rectly in the form of a current signal to the diode
gate network of the vertical switching circuit. The
current signal for vertical positioning of the trace
is added to the current signal in the second
amplifier, and is controlled by VR54/VR154 in the
positioning circuit.
A signal within each of the second amplifiers is
amplified by Q10 or Q111, and fed to the vertical
switching circuit as an internal trigger signal. At
CH1, a signal is also fed to the CH1 Output terminal
through impedance converter Q11.
The vertical switching circuit determines whether
the CH1 or the CH2 preamplifier signal, or both, will
be connected to the vertical output amplifier circuit.
This circuit is comprised of diode gate circuits,
which electronically switch the vertical signals of
CH1 and CH2, and a switching buffer (Q201, 202)
which provides the switched signals to the vertical
output amplifier. The switching buffer output is
routed through a delay line (DL1) which allows the
sweep waveform to start before the vertical signal
is applied to the CRT.
Drive amplifier Q301/Q302 in the vertical output
amplifier is a feedback amplifier, with a low output
impedance for driving the final amplifier. The final
amplifier circuit provides the final amplification for
the signal and applies it to the vertical deflection
plates of the CRT. Transistors Q303-Q306 supply
the necessary current for driving the final stage tran-
sistors, Q307—Q310. The signal is voltage-amplified
in this stage and fed to the CRT for vertical deflec-
tion.
HORIZONTAL/TIME BASE
The trigger generator is comprised of a pulse
generator circuit which produces a trigger pulse sig-
nal for driving the sweep generator, and an AUTO
circuit which produces a free-running signal for au-
tomatic sweep operation when no trigger is applied.
The trigger pulse generator circuit includes a source
switch (S401), a coupling switch (5402), an imped-
ance converter (Q403), a level comparator (Q404,
Q405), a TV synchronization separator (Q410,
Q411), and a Schmitt trigger circuit (IC401).
The source switch selects the internal trigger signal
fed from Q401, the line trigger signal from R1025,
or an external signal from P405. The selected signal
is fed to the coupling switch.
The coupling switch selects the mode of trigger cou-
pling. In the AC, HF REJ and TV modes, the DC
component of the trigger signal is blocked by cou-
pling capacitor C409 and the frequency components
below 10 Hz are attenuated. In the HF RE] trigger
coupling mode, the high frequency components of
the trigger signal above about 50 kHz are attenuated,
while the lower frequency components (between
about 10 Hz and 50 kHz) are passed without attenua-
tion. In the TV mode, the sync signal is separated
from the video signal by the TV synchronization
separator. The DC mode of trigger coupling passes
all signals from DC to 25 MHz and above.
Impedance converter Q403 is an FET source fol-
lower. It provides a high input impedance for the
trigger signal and operates as a buffer between the
trigger generator circuit and the trigger signal
sources. The output signal from the impedance con-
verter is fed to the level comparator circuit. i
The level comparator (Q404, Q405) is a differential
amplifier which selects the rising edge (or the falling
edge) of the impedance converter output signal. The
comparator highly amplifies any voltage difference
between the impedance converter output and the re-
ference level from the Level control VR441/S441. At
the Fix position of the Level control, the trigger point
is locked at the center portion of the trigger range
by feeding the output of the level fixing circuit
(Q406—Q409) back to Q405.
The slope of the trigger signal is selected by Slope
switch S403.

The output signal of the level comparator is fed to
the buffer amplifier (Q410-413) and amplified suffi-
ciently to drive Schmitt trigger circuit IC401. The
output of IC401 drives the sweep generator and the
auto circuit (Q601, Q602) which converts the high
speed pulse signal of the Schmitt trigger circuit into
a DC signal for operating the sweep generator in the
Auto mode.
The sweep generator includes a sweep gate circuit
(IC601-1/2), a sweep start comparator (Q603, Q604),
a sweep enable circuit (IC601-1/2) a hold off circuit
(Q613), a sawtooth sweep generator and a sweep
length circuit (Q616). The sawtooth sweep generator
is comprised of a gate transistor amplifier, a Miller
integrator, an integration time constant switching
circuit and a SEC/DIV switch which controls the
switching circuit.
The sweep generator produces the sawtooth voltage
that is amplified by the horizontal amplifier to pro-
vide horizontal deflection on the CRT. This circuit
also produces the gate waveform used by the Z-axis
circuit to unblank the CRT during the sweep time.
Gate transistor amplifier Q603 alternately resets the
two selectable sweep ramp capacitors (C606/607 or
C606/607/608) through Q605 and Q606 or allows the
capacitors to charge. A constant current from Q608
generates a bias (zero) current through R618, Q612,
D621, D622, and R621. A current selected by the
SEC/DIV switch is generated by the IC603/Q611 cir-
cuit and charges the sweep capacitors also through
the same bias circuit. The current difference produc-
esaramp at R621.
The sawtooth voltage ramp is fed to the horizontal
output amplifier through switching circuit 1C602,
which selects the internal or external signals.
The horizontal output amplifier consists of a drive
amplifier and an output amplifier. The drive
amplifier (Q801-Q804) converts the single-ended
signal from the switching circuit into a push-pull
signal for driving the output amplifier. The gain of
this amplifier can be multiplied by a factor of 10
for the x 10 MAG operation.
Page 19
The output amplifier (Q805-Q812) which consists
of two single-ended feedback amplifiers, amplifies
the signal at its input to produce the output to drive
the horizontal deflection plates of the CRT. The sig-
nal current amplified by Q805 and Q806 is con-
verted into a voltage signal by Q807-Q812 to obtain
a sufficiently high level and a low output imped-
ance. By means of negative feedback resistors (R817,
R818), stable gain and a wide flat frequency response
are achieved.
CALIBRATOR
The calibrator circuit provides a square-wave output
signal with an accurate voltage of 2 V p-p (= 2%)
which is used to calibrate the vertical deflection fac-
tor. The calibration signal is produced by generating
a signal with the multivibrator (1C4001-1/4, 2/4),
shaping the waveform with the Schmitt circuit
(IC4001-3/4,4/4), and dividing the voltage signal
with resistors R4009-4012.
CRT CONTROL
The CRT control circuit provides the voltage levels
and control circuits necessary for operation of the
CRT. Q2001 and its associated circuitry compose the
high-frequency oscillator which produces the drive
for high voltage transformer T2001. The high voltage
output is rectified by D2010 and D2011, and con-
verted into —2000 volts DC. This high voltage is
supplied to the CRT cathode as an acceleration volt-
age, and is stabilized by the regulator circuit
(1C2001).
POWER SUPPLY
The low voltage power supply circuit supplies the
operating power for the Oscilloscope from four regu-
lated power supplies (+160 V, +5 V, +12V, —12
V) and one unregulated power supply (+16 V). The
output voltages of the two windings of the power
transformer are rectified and then regulated.

Page 20
MAINTENANCE & ADJUSTMENTS
GENERAL MAINTENANCE
Preventive Maintenance — Clean and recalibrate the
Oscilloscope on a regular basis to keep the instru-
ment looking nice and working well.
Cleaning — Remove any dirt, dust and grime
whenever they become noticeable. You can remove
dirt from the outside covers with a soft cloth moist-
ened with a diluted household cleaning solution.
Recalibration — Recalibrate the Oscilloscope at reg-
ular intervals; after 1000 hours of operation, for ex-
ample, or twice a year if used daily.
Servicing — Should the Oscilloscope ever become
inoperative or damaged, refer servicing to a qualified
repair facility.
ADJUSTMENT AND CALIBRATION
WARNING: Be careful when you are calibrating the
Oscilloscope; dangerous high voltage is present in
several areas.
12V
=12y
+5V
+160V
VERT. PCB
VR1006
a9
+12v ADT
Rear side
NOTE: Some controls are factory preset and are not
included in this calibration procedure. These need
no adjustment unless you replace those parts. In this
event, contact the Heath Customer Service depart-
ment.
Power Supply Adjustments (Figure 11)
1. +12V adjustment — Adjust VR1006 for +12
+ 0.05 V between pin 2 on connector P1007
and ground. Adjust this voltage very care-
fully, as it provides a reference for other
supplies.
2; —12V check — Check pin 3 on P1007 for
proper voltage, —12 = 0.2V.
3. +5Vcheck — Chec'kvbinr‘} on P1007 for pfoi)-
er voltage, +5V = 0.25V.
4. +160V check — Check pin 6 on P1007 for
proper voltage, +160V = 5V.
—2000V check — Check pin 3 on connector
P2005 for —2000V = 50V. Use a high input
impedance voltmeter (10 MQ or more) rated
for high voltage measurements.
w
HORIZ. PCB
Rear side
Figure 11
Check points of DC supply.