Tektronix 3B4 User manual

INSTRUCTION
MIAN UAL Serial Number
Tektronix, Inc.
S.W. Millikan Way @ P. O. Box 500 ® Beaverton, Oregon 97005 @ Phone [phone] @ Cables: Tektronix
070-431 964

SECTION 1
CHARACTERISTICS
Introduction
The Type 3B4 Time Base plug-in unit is designed to be
used primarily with the Tektronix Type 561A Oscilloscope sys-
tem; however, It can also be used with the other 560-Seriés
systems that use 3B-Series plug-in units such as the Type 564
and Type 567. As part of an oscilloscope system, the Type
3B4 is used as an accurate time base generator or as a
calibrated amplifier for externally generated deflection sig-
nals,
When used with the 567 or RM567, the 3B4 provides a time-
base, but does not activate the digital readout circuitry.
In the 565 or RM565, the 3B4 provides a vertical time-base
for raster applications but does not provide retrace blanking.
The Type 3B4 provides calibrated sweep rates from 0.05
psec/div to 5sec/div in 25 calibrated steps. A five-step,
direct-reading magnification feature provides magnification
up to 40X or 50X, depending on the sweep rate to which
magnification is applied. When the Type 3B4 is used as an
amplifier for externally generated deflection signals, the
magnifier provides five steps of deflection sensitivity, from
0.2 volts/div to 5 volts/div. In addition, a variable control
provides uncalibrated sweep rates and deflection sensitivities
between the calibrated steps. By using the variable control,
uncalibrated sweep rates from 0.05 psec/div to approxi-
mately 12.5 sec/div and deflection sensitivites from 0.2 volts/
div to approximately 12.5 volts/div are available. Uncali-
brated operation is indicated by a neon lamp.
Normally, the Type 3B4 is inserted in the right-hand com-
partment (operator's right, oscilloscope’s left) of the oscillo-
scope and in this position provides horizontal deflection.
When used with the Type 561A, the Type 3B4 can be inserted
into the left-hand compartment of the oscilloscope to provide
a time base that runs vertically on the crt screen. Due to
differences in the horizontal and vertical deflection plate
sensitivities, the Type 3B4 must be calibrated for vertical
deflection use if accuracy is required in such application.
This manual is written with the assumption that the Type 3B4
will normally be used to provide horizontal deflection sig-
nals in a Type 561A.
Triggering
Facilities
TRIGGER MODE Switch Free Run, Auto, Normal,
and Single Sweep
TRIGGERING LEVEL Con- See Tables 1-1 and 1-2.
trol
SLOPE Switch + or —
COUPLING Switch Ac, Ac Low-Frequency Re-
ject, and Dc
SOURCE Switch Internal, Line, External,
and External + 10
TRIGGERING LEVEL Control Voltage Range (external
triggering}
See Table 1-1.
TABLE 1-1
Voltage Range
SOURCE COUPLING Typical Minimum
AC, DC or
EXT AC LF REJ +19 ¥ +15
AC or DC +190 v
EXT + 10 AC LF REJ +150 v
NOTE
The voltage range of the TRIGGERING LEVEL con-
trol indicates the maximum external peak voltage
that will permit triggering at any amplitude point
on the signal. Signals with greater amplitudes can
be used and will provide triggering, but the range
of trigger-point selection is still limited to the TRIG-
GERING LEVEL control voltage range.
Triggering Sensitivity. See Table 1-2.
@1
TABLE 1-2
SOURCE
Voltage Range
AC
AC LF REJ DC
INT
1 minor division of
deflection 30 cps to 20
mc. Outside these
limits requires larger
triggering signal.
1 minor division of
deflection 30 kc to 20
mc. Outside these
limits requires larger
triggering signal.
1 minor division of
deflection dc to 20
me (with trace verti-
cally centered}, Above
20 mc requires larger
triggering signal,
EXT
0.5v 30 cps fo 20 mc.
Outside these limits
requires larger trig-
gering signal.
0.5v 30kc to 20mc.
Outside these limits
requires larger trig-
gering signal.
0.5v dc to 20mc.
(with trace vertically
centered). Above 20
mc requires larger
triggering signal.
1-1

Characteristics—Type 3B4
Automatic Triggering. In this mode of operation a
bright-line sweep is displayed automatically in the absence
of a trigger. The sweep triggering characteristics stated pre-
viously also apply for automatic triggering except that the
triggering signal must be higher than about 20cps. The
TRIGGERING LEVEL control operates when a triggering sig-
nal is present.
Single Sweep. This feature permits only one triggered
sweep following each reset pulse. The reset pulse is gen-
erated by pressing the PUSH TO RESET button. The trigger-
ing characteristics stated previously apply.
EXT TRIG IN Connector Input Characteristics. See Table
1-3.
TABLE 1-3
TRIG
729
fe)
Rp
|
—0o
ot
Rp Input
SOURCE | COUPLING| C, C, {Meg ©) {Voltage
(pf) Max Peak
DC 220 [shorted [ ~1 +75
EXT AC 20 |=0.01 ph] = +500
AC LF REJ | =20 |100 pf | 0.09 | +500
EXT DC = shorted | 10 500
+ AC = 20.01 wf} 10 +500
10 AC LF REJ | 20 |=100pf | = +500
Sweep
Facilities
TIME/DIV 0.2 psec/div to Ssec/div in 23 steps, I,
Switch 2, 5 sequence. The calibration accuracy
(unmagnified) is 3% from 0.2 wsec/div
to 2 sec/div; 5% at 5 sec/div.
VARIABLE Uncalibrated variable time/div control.
Control Multiplies the sweep time/div of any step
of the TIME/DIV switch by a factor vari-
able from 1 to >2.5.
POSITION Coarse horizontal positioning to position
Controls any portion of the trace to the center of
the crt. The FINE control has a range of
about 2 minor divisions.
MAGNIFIER Provides direct readout magnification of
Control the sweep (up to 50°). The magnifier also
provides the 0.05 and 0.1 psec/div sweep
rates. Magnified sweep accuracy, —-5%
(exception: 5 sec/div). Magnified sweep
registration, +1 minor division,
1-2
+ GATE OUT Provides a +20-volt (+15%) output pulse
Connector during sweep time.
Sweep Length 10.5 +0.3 major division.
Sweep Amplifier (when used as an external hori-
zontal amplifier)
Facilities
HORIZONTAL Calibrated volts/div steps of 0.2, 0.5, 1,
VOLTS/DIV 2, and 5 volts/div. Accuracy +3% when
Switch calibrated to match the oscilloscope in
which used. The amplifier is de coupled
to the EXT HORIZ IN connector.
VARIABLE Multiplies volts/div of any step by a factor
Control variable from 1 to >2.5.
EXT HORIZ Input R and C is typically 1 megQ shunted
IN Con- by 40 pf.
nector
Frequency De to 400 kc. Response <30% down at
Response 400 ke with the VARIABLE control set to
CALIB position.
Maximum Input +20 volts dc, or 20 volts peak ac.
Voltage
Environmental
Operating
TEMPERATURE 0° C to +50° C.
ALTITUDE 10,000 feet maximum.
VIBRATION 0.015 inch peak-to-peak, (1.9 Gs) for 15
minutes along each axis. Vibration fre-
quency varied from 10-50-10 cps in 1-
minute cycles.
Non Operating
TEMPERATURE —35° C to +60° C.
ALTITUDE 50,000 feet maximum.
VIBRATION —0,015 -£0.003 inch total displacement from
10 to 5 cycles.
TRANSIT Meets National Safe Transit type of test
when factory packaged: Vibration for one
hour at slightly greater than 1G. 30-inch
drops on corners, edges and flat surfaces.
Mechanical
Construction Aluminum-alloy chassis with chrome-plated
side rails. Front panel is photo-etched
and anodized.
Dimension 6%, inches high, 4%, inches wide, 147,
(approx.) inches deep (overail).
Net Weight 4.5 pounds.
Accessories
Information on accessories for use with this instrument is
included at the rear of the mechanical parts list.
—

SECTION 2
OPERATING INSTRUCTIONS
Front-Panel Controls and Connectors
See Fig. 2-1.
NOTE
A more complete description of the controls and
connectors is included under ‘‘Standard Sweep Op-
eration” later in this section.
TRIGGER MODE Selects the manner in which the Time Base
Switch
FREE RUN
AUTO
NORM
SINGLE
SWEEP and
PUSH TO
RESET
SOURCE
INT
LINE
EXT
and
EXT + 10
COUPLING
AC
AC LF REJ
DC
sweeps are initiated. For example:
In this position, recurrent sweeps are pro-
vided. The completion of one sweep
causes the next to begin.
Automatic sweep. Permits each sweep to
be triggered when the triggering-signal
repetition rate is about 20 cps or greater.
For lower repetition rates or in the
absence of a triggering signal, the sweeps
are recurrent, as in the FREE RUN posi-
tion.
Normal method of operation. Each sweep
is triggered by the signal from the inter-
nal trigger generator,
Often used when displays of non-repetitive
signals are photographed. When the lamp
inside the PUSH TO RESET button is lit, the
time base is ready to produce one trig-
gered sweep.
Selects the source of the triggering signal:
Internal. Obtains the sweep triggering
signal from the vertical plug-in unit.
Obtains the sweep triggering signal from
a low-voltage winding on the oscilloscope
power transformer.
Permits external signals applied to the
EXT TRIG IN connector to be used for
sweep triggering. High-amplitude _ trig-
gering signals can be attenuated by using
the EXT + 10 position.
Permits acceptance or rejection of some
triggering signal characteristics:
Rejects dc and attenuates very low-fre-
quency ac triggering signals.
Ac low-frequency reject. Rejects de and
discriminates against low-frequency ac
triggering signals. The 30% down point
is 17 ke.
Accepts ac and dc triggering signals,
SLOPE (+ or —) Determines whether triggering will occur
during the positive-going (+) or negative-
going (—) portion of the triggering signal.
TRIGGERING
LEVEL
TIME/DIV OR
HORIZONTAL
VOLTS/DIV
MAGNIFIER
VARIABLE
&
Selects the amplitude point on the trigger-
ing signal where triggering will occur.
Provides 23 calibrated display sweep rates
(unmagnified}. See Fig. 2-1. The number
opposite the dot on the MAGNIFIER knob
skirt always indicates the sweep time per
centimeter as long as the VARIABLE con-
trol is in the CALIB position. The number
bracketed by the two heavy black lines
on the clear plastic knob flange is the un-
magnified sweep time per division. To
change the unmagnified sweep rate, the
concentric flange and the MAGNIFIER
knob must first be interlocked by posi-
tioning the dot on the MAGNIFIER knob
between the two heavy black lines on the
flange. When the flange is positioned so
that the two black lines bracket the EXT
HORIZ IN position, any signal connected
to the EXT HORIZ IN connector is applied
to the horizontal amplifier. In this position
of the switch, the amplified externally
generated signal provides horizontal de-
flection.
Provides magnification of the time base
display up to 40X or 50X in five direct-
reading steps (Magnification of the four
fastest unmagnified sweep rates is limited
to 0.05 psec/div). For example, at 10
magnification, the 5 minor division seg-
ment at the center of an unmagnified crt
display is horizontally expanded to full
graticule width. Any other 5 minor divi-
sion segment of the original unmagnified
display may then be observed in magnified
form by turning the POSITION controls.
To determine the degree of magnification,
divide the number bracketed by the two
black lines on the clear plastic flange by
the number adjacent to the dot on the
MAGNIFIER knob.
Provides continuously variable uncalibrated
sweep rates between about 0.4 and 1.0
times that indicated by the TIME/DIV
switch. Whenever the VARIABLE knob is
not set to CALIB, the UNCAL lamp lights.
When the TIME/DIV switch is set to the
EXT HORIZ IN position, the VARIABLE
knob provides ~ 2.5:1 change in horizontal
amplifier sensitivity.
STANDARD SWEEP OPERATION
The control and switch settings listed under ‘First-Time
Operation" later in this section establish the basic condi-
tions necessary for most measurements. In many applications,
it is desirable for a repetitive signal to produce a stationary
2-1

Operating Instructions—Type 3B4
2-2
TYPE 3B4 TIME BASE
FINE VARIABLE
POSITION TIME/DIV or Tite
HORIZONTAL VOLTS/DIV 2
VOLTS/DIV
PULL MAG
TRIGGER MODE
AUTO NORM
FREE
RUN
SLOPE COUPLING SOURCE
TRIGGERING
AC
INT
EXT
LEVEL
Fig 2-1. Front Panel Controls and Connectors
_——
——

display on the crt so the waveform can be examined in
detail. For this type of display, the start of each sweep
must bear a definite fixed-time relationship to the events
in the input signal. This can be accomplished by using the
displayed signal or another related signal to start (trigger)
single or repetitive sweeps. The following is a detailed
description of the control and switch settings which provide
complete control over the means of triggering the sweep.
It is assumed that the oscilloscopes system is a Tektronix
Type 561A.
TRIGGER MODE
FREE RUN. Free-running operation produces continuously
repetitive sweeps even in the absence of a triggerifg signal.
These sweeps provide a reference trace, as does the AUTO
position. This method of operation is useful in applications
where a device under test requires a trigger or input signal.
The front-panel +GATE OUT signal may be used to operate
the device under test. The resulting signal displayed on
the crt will then be synchronized with the sweep.
AUTO. This position is frequently used for ease of opera-
tion and because of the reference trace produced in the
absence of a triggering signal. The time base free runs with-
out the application of a trigger. If a triggering signal is
received, the free running is interrupted, but this first event
in the signal does not trigger a sweep. If the first signal
event is followed by a second event within about 80 msec,
a triggered sweep is initiated, and if not, the free running
resumes, Since the dormant period is limited to about 80
msec, signal frequencies below about 20 cps cannot produce
a triggered sweep in the AUTO mode. For such signals, the
NORM mode of operation is used.
With the SOURCE switch set to INT and the TRIGGER
MODE switch set to AUTO, the sweep will trigger on any
signal that will trigger the NORM mode (about 1 minor
division of deflection) so long as the triggering signal is
above about 20 cps. When operating in the AUTO mode,
it is necessary to adjust the TRIGGERING LEVEL contro! to
lock the sweep with the triggering signal.
NORM. In the NORM or normal mode, the time base is
dormant in the absence of a triggering signal. Each sweep
must be initiated by a triggering signal.
SINGLE SWEEP. Single sweep is often used when photo-
graphing non-reptitive waveforms and in other applications
where the vertical input signal continually varies in amplitude
shape, or time interval. A continuous display of such signals
would appear as a jumbled mixture of many different
waveforms and would yeild little or no useful information.
The Type 3B4 permits a single sweep to be presented with
the elimination of all subsequent sweeps. The information
in the one sweep is thus clearly recorded without the con-
fusion resulting from multiple nonrepetitive traces.
When the TRIGGER MODE switch is set to SINGLE SWEEP,
the time base becomes inoperative. The time base can be
“reset” to the triggerable condition by pressing the RESET
button. If there is sufficient delay before triggering, the
RESET lamp will light to show that the time base is ready to
be triggered. When the time base has been triggered and
one sweep completed, the time base again becomes inopera-
tive and the lamp extinguishes.
@
Operating Instructions—Type 3B4
SOURCE
INT. It is usually easiest to obtain the sweep triggering
signal internally (INT) from the vertical deflection system.
LINE. If the displayed signal frequency is related to the
power-line frequency, the line source can be used. This
source is useful when the displayed signal does not allow
internal triggering.
EXT. External triggering is often used when signal tracing
in amplifiers, phase-shift networks, and wave-shaping circuits.
The signal from a single point in the circuit can be connected
to the EXT TRIG IN connector through a signal probe or a
cable. With this signal triggering the sweep, it is possible to
observe the shaping, amplification, and time relationship of a
signal at various points in the circuit without resetting the
triggering controls.
EXT. + 10. The only difference between external (EXT)
and external divided-by-10 {EXT + 10) is that the latter
attenuates the external triggering signal. Attenuation of high-
amplitude external triggering signals is desirable to broaden
the TRIGGERING LEVEL contro! range.
DC. De coupling allows the trigger circuits to receive
signals of all frequencies from de upward. It is best to de
couple for very low-frequency signals (below about 20 cps).
AC. Ac coupling rejects the de component of triggering
signals and increasingly attenuates ac triggering signals as
the frequency decreases. This position of the coupling switch
is not normally used for triggering signals below about 20
cps, but this is the most used position of the switch.
AC LF REJ. Ac low-frequency reject coupling rejects the
dc component of triggering signals and increasingly attenu-
ates ac signals as frequency decreases (30% down point
17 ke). If line-frequency hum is mixed with a desired high-
frequency triggering signal, best results are obtained by
using this position of the COUPLING switch.
Ac low-frequency reject coupling should also be used
when triggering internally from multi-trace plug-in units
operated in the alternate-trace mode (unless the “trigger
from a single channel only” feature of the plug-in is used).
For additional information, see the multi-trace vertical plug-
in unit instruction manual.
SLOPE
Sweeps can be triggered during either the rising or falling
portion of the triggering signal. When the display consists
of several cycles of the input signal, either setting of the
SLOPE switch may be used. However, if it is desired to
display less than one full cycle of the input signal, the SLOPE
switch permits the sweep to start on either the rising (+
slope) or falling (— slope).
TRIGGERING LEVEL
The TRIGGERING LEVEL control determines the instanta-
neous voltage on the triggering signal at which the sweep is
triggered, (This instantaneous voltage can also include a dc
2-3

Operating Instructions—Type 3B4
level if the COUPLING switch is set to DC.) With the SLOPE
switch at +, adjusting the TRIGGERING LEVEL control makes
it possible to trigger the sweep consistently at virtually any
point on the positive slope of the triggering signal. Like-
wise, with the SLOPE switch at —, adjusting the TRIGGER-
ING LEVEL control makes it possible to trigger at virtually
any point on the negative slope of the triggering signal.
TIME/DIV OR HORIZONTAL VOLTS/DIV
The Time Base has 23 calibrated sweep rates ranging from
0.2 usec/div to 5sec/div (unmagnified }. See Fig, 2-2. The
number opposite the dot on the MAGNIFIER knob indicates
the sweep time per division as long as the VARIABLE con-
trol is in the CALIB position, The unmagnified sweep rate
value being used appears between the two black lines on
the clear plastic flange of the TIME/DIV control. The VARI-
ABLE control and MAGNIFIER switch, used in conjunction
with the TIME/DIV switch, permit the sweep rate to be varied
continuously between 50 nsec/div and about 12.5 sec/div.
The MAGNIFIER switch is discussed under “MAGNIFIER”.
All sweep rates obtained with the VARIABLE control in any
but the fully clockwise position are uncalibrated, Uncali-
brated sweep rates are indicated when the UNCAL lamp is
lit.
VARIABLE
TIME/DIV or YNPAS
HORIZONTAL VOLTS/DIV
|
ExT
HORIZ IN
Fig. 2-2. TIME/DIV OR HORIZONTAL VOLTS/DIV and MAGNIFIER
KNOBS.
When the flange is positioned so that the two heavy black
lines bracket the EXT HORIZ IN position the horizontal am-
plifier input is connected to the EXT HORIZ IN connector
and accepts external horizontal deflection signals, In this
mode of operation, five ranges of horizontal deflection sen-
sitivity are available. The five sensitivity ranges are from
0.2 volts/div to 5 volts/div.
To position the TIME/DIV switch to the EXT HORIZ IN
position, turn the MAGNIFIER knob until the dot on the knob
2-4
is positioned between the two black lines on the clear plastic
flange. Turn the knob until the two black lines on the flange
bracket the position marked “EXT HORIZ IN". The external
horizontal deflection sensitivity may now be selected by
pulling the MAGNIFIER knob outward to unlock it, then,
while holding the knob out, turn it to the desired volt/div
position,
MAGNIFIER
The sweep ranges between 5 sec/div and 2 usec/div can
be magnified up to 40 or 50 in 5 steps. The degree of
magnification is the ratio between the indicated magnified
rate (number opposite the dot on the skirt of the MAGNI-
FIED knob) and the indicated unmagnified rate (number
bracketed by two black lines on the clear plastic flange).
Since the magnified display rate is always direct reading,
it is seldom necessary to determine the actual magnifying
factor used.
Above 2 ysec/div the number of steps of magnification
decrease until at the .2 uSEC setting of the TIME/DIV switch
only two steps of magnification are available. The .2 .SEC
postion is the highest sweep rate to which the TIME/DIV
switch can be set, but by the use of the two additional mag-
nified positions, and effective sweep rate of 50 nSEC/DIV is
obtained.
FIRST-TIME OPERATION
The following contro! and switch settings for the Type
3B4 can be used for a wide range of measurements, The
operating conditions established by these settings also pro-
vide a starting point for the operator who is learning to
use the instrument.
TRIGGER MODE AUTO
COUPLING AC
SOURCE INT
VARIABLE (TIME/DIV} CALIB [fully clockwise}
MAGNIFIER Locked to TIME/DIV
switch
The Type 384 now provides the time base for measure-
ments of vertical deflection signals above about 20 cps. In
many cases, only the TIME/DIV switch and the TRIGGER-
ING LEVEL control require readjustment when progressing
from one measurement to the next.
The appropriate TIME/DIV switch setting depends on the
frequency of the applied signal and the type of measurement.
For example, to observe about 2 cycles of the oscilloscope
60 cycle Calibrator signal, set the TIME/DIV switch to 5
mSEC.
The following conditions must exist to obtain a triggered
display of the vertical deflection signal with the preceding
control settings:
1. The frequency of the vertical deflection signal must
be about 20 cps or greater (below 20 cps, the TRIGGER
MODE switch must be set to NORM).
2. At SOke the vertical deflection amplitude must be at
least 1 minor division. See Table 1-2.

3. The TRIGGERING LEVEL control must be properly ad-
justed,
lf the first two conditions are met, a stable display will
be obtained with the TRIGGERING LEVEL control set near
zero. When the observed deflection amplitude is a fraction
of a division, the range of adjustment is relatively narrow
but broadens with increased vertical deflection.
Operating Techniques
The following procedures are designed to acquaint the
operator with the functions of the various controls on the
Type 3B4, -
Example 1, Time Measurement: This example explains
how to measure the time of one-half cycle of the calibrator
square-wave output. Set the Type 3B4 controls as outlined
in Table 2-1.
TABLE 2-1
Typical Control Settings For Time Measurements
Control | Settings
TRIGGER MODE AUTO
TIME/DIV ] mSEC
MAGNIFIER 1] mSEC
SLOPE {(—)
COUPLING AC
SOURCE INT
VARIABLE CALIB
With the controls set as outlined in Table 2-1, apply a
2-volt signal from the calibrator to the input of the vertical
plug-in amplifier. Set the VOLTS/DIV switch on the vertical
plug-in for 4 divisions of vertical deflection. Turn the verti-
cal plug-in POSITION controi until the vertical deflection ex-
tends 2 divisions above and 2 divisions below the horizontal-
ly scribed centerline. Turn the POSITION and FINE controls
until the 50% point on the positive half-cycle of the square
wave starts 1 division from the left edge of the graticule.
With the equipment properly calibrated, the 50% point on
the trailing edge of the halfcycle occurs 8.33 divisions to
the right of the 50% point of the leading edge. Since the
TIME/DIV switch is set to 1 mSEC, the positive half-cycle of
the square wave is 8.33 msec long.
Operating Instructions—Type 3B4
Example 2, Risetime Check: At the completion of the meas-
urement listed in Example 1, unlock the MAGNIFIER knob
by pulling it out, then, while holding it out, set it to the
20 wSEC position. Using the POSITION control, position the
leading edge of the positive half-cycle at the vertically-
scribed centerline. Using the POSITION and FINE controls,
carefully reposition the leading edge until the 10% point on
the pulse crosses the horizontally-scribed centerline 2 minor
graticule divisions up from the start of the pulse. After the
leading edge of the pulse is properly positioned, note the
position of the 90% point of the rise. Since there is no easy
point of reference from which to read, use the POSITION
contro! of the vertical plug-in amplifier to move the 90%
point down to the horizontally-scribed centerline. The 90%
point will intersect the horizontally-scribed centerline less
than one major graticule division to the right of the vertical-
ly-scribed centerline, thus providing a 10% to 90% risetime
of less than 20 psec.
Example 3, Type 3B4 Used as a Trigger Source: Ordi-
narily, the signal to be displayed is also used to trigger the
oscilloscope. In some instances, it may be desirable to re-
verse this situation. The sweep-related output pulses, avail-
able at the front panel of the Type 3B4 can be used as the
input or triggering signal for external devices. The output
signal of the external device will then produce a stable dis-
play while the oscilloscope free runs. For this type of opera-
tion, set the controls on the Type 3B4 as listed in Table 2-1
except set the TRIGGER MODE switch to FREE RUN. Con-
nect the Type 3B4 +GATE OUT output to the external de-
vice to be triggered. Since the external device is now being
triggered with a signal that has a fixed time relationship
to the oscilloscope sweep, the output of the external device
will produce a stable display on the oscilloscope, as though
the oscilloscope were triggered in the normal manner.
Example 4, External Horizontal Deflection: For special
applications, it is possible to produce horizontal deflection
with an externally derived signal. This permits the oscillo-
scope system to be used to plot one function against an-
other (e.g. Lissajous figures). However, the system is not
intended for precise phase-angle measurements.
To use an external signal for horizontal deflection, con-
nect the signal to the EXT HORIZ IN connector. Set the
TIME/DIV OR HORIZONTAL VOLTS/DIV switch to EXT
HORIZ IN.
Sensitivity of the horizontal deflection system is changed
by changing the MAGNIFIER switch when using external
horizontal deflection. To change sensitivity, pull the MAG-
NIFIER knob out to unlock it, then set it to the selected
position of the SEC OR EXT VOLTS positions.
2-5

NOTES

SECTION 3
CIRCUIT DESCRIPTION
Introduction
This section contains the theory of operation of the various
circuits in the Type 3B4. The discussions are supported by
the block diagram and schematics in Section 5. The relation-
ship of the circuits in a particular block to those in other por-
tions of the system is discussed in the description of that
block.
The block diagram in Section 5 shows the basic elements of
the Type 3B4. The Trigger Generator blocks select and
shape triggering signals and apply trigger pulses to the
Sweep Generator blocks. The Sweep Generator generates a
linear-ramp horizontal deflection voltage, and in addition,
adapts externally generated signals to provide horizontal
deflection when such operation is desired. From the Sweep
Generater blocks, the horizontal deflection signals are
applied to the Horizontal Amplifier, where they are split in
phase and amplified sufficiently to provide the degree of
magnification being used.
Trigger Generator
For best triggering stability, the Sweep Generator requires
trigger pulses that are representative of the triggering fre-
quency but with greater wave-shape consistency than the
signals generally encountered. The Trigger Generator con-
verts the triggering signal into a pulse having a consistently
fast risetime while retaining the characteristic repetition fre-
quency of the triggering signal. The converted pulse is then
used to trigger the Sweep Generator, which generates the
time base.
The signal to be used for triggering is selected by means
of SOURCE switch SW5 (see Trigger Generator schematic)
from one of three sources: the vertical plug-in (INT); a low-
voltage winding on the oscilloscope power transformer
(LINE}; or from an external signal applied to EXT TRIG IN
connector J1 (EXT).
COUPLING switch SW8 selects which of the three input
coupling methods is to be used; ac, ac with low frequencies
rejected, or de. From the COUPLING switch, the signal is
applied through SLOPE switch SW10 to one side of a long-
tailed comparator circuit (V24 and associated circuit elements)
used as a trigger recognizer.
In operation, V24A in the comparator is kept cut off by
V24B until the selected point on the triggering signal occurs.
With SLOPE switch SWI10 in the + position, TRIGGERING
LEVEL control RI6A applies conducting bias to V24B. With
V24B conducting, the current flow through R22 develops a
voltage which keeps V24A cut off. When the triggering sig-
nal goes positive to the selected trigger point, V24A starts
to conduct and cuts off V24B. If the SLOPE switch is set to
—, TRIGGERING LEVEL control R16A is set to deliver cut-
off bias to V24A while V24B is permitted to conduct due to
its grid being grounded through R10 and R7. As the trigger-
ing signal goes negative, it reaches a point where it cuts off
V24B. With V24B cut off, V24A is forced into conduction by
virtue of the —100 volts applied to its cathode through R22.
@
During the time that V24A is cut off and the comparator is
waiting for the proper triggering conditions to occur, current
flow through R24 and R26 develops cutoff bias for Q24 since
the emitter of Q24 isistrapped to the +125 volt supply
through diode D28. When the comparator is switched by
the triggering signal and V24A starts to conduct, the con-
duction of V24A reverses the current flow through R24 and
applies
conducting bias to Q24. Also during the time the
comparator is waiting to be switched, tunnel diode D30 is
biased to its low voltage state (see Fig. 3-1} by the voltage
developed across R32 and L32. When Q24 is biased into
conduction by the switching of the comparator, the conduc-
tion of Q24 provides about 2.5 ma of current to D30 which
causes D30 to switch to its high voltage state.
—_— ow a oe > —<_
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A
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i Voltage | |
==65 mv 22350 mv 500 mv
Low-Voltage High-Voltage
State State
Fig. 3-1. Current-Voltage Characteristics of a Typical Tunnel Diode.
The switching of a tunnel diode from its low voltage state
to its high voltage state is extremely fast. When D30
switches to its high voltage state due to the turning on of
Q24, the jump in voltage across D30 appears on the base
of Q34. Q34 is normally conducting, and the sudden in-
crease in its base to emitter voltage causes a corresponding
increase in current. The sudden demand for current by Q34
is met by drawing current from C33. Since the time constant
of the circuit is short, the current increase through @34 is
in the nature of a sharp pulse. The pulse is coupled out
through T38 of the Sweep Generator.
Sweep Generator
Outputs and Triggering. When the TIME/DIV OR HORI-
ZONTAL VOLTS/DIV switch is set to any of the TIME/DIV
3-1

Circuit Description—Type 3B4
positions, the Sweep Generator (see Block Diagram) produces
four simultaneous output signals:
1. A positive-going sawtooth that is applied to the Hori-
zontal Amplifier.
2. A negative-going crt unblanking pulse with the same
time duration as the sweep sawtooth rise. This pulse is
coupled to the oscilloscope crt.
3. A positive-going pulse with the same duration as the
sweep. This pulse is coupled to the front-panel +GATE OUT
connector for external use.
4. A negative-going multi-trace syne pulse. This pulse is
applied to the vertical plug-in unit interconnecting socket. The
pulse is used to switch channels in a multi-trace plug-in unit
when operating in the alternate mode.
In most applications, each cycle of events is started by a
trigger pulse from the Trigger Generator, However, it is
also possible to free run the Sweep Generator; that is, the
end of one cycle causes the next cycle to begin. The desired
operation is selected by the TRIGGER MODE switch. The
four operating modes provided by the TRIGGER MODE
switch are described in Section 2 of this manual.
The Sweep Gating circuit is an electronic switch that
drives the Disconnect circuit to switch the Disconnect Diodes
on and off. When the Disconnect Diodes are switched off,
the Miller Runup Integrator begins to produce a sawtooth
that is fed back through the Lockout circuit to the Sweep
Gating circuit. When the sawtooth reaches the desired am-
plitude, the Lockout circuit resets the Sweep Gating tunnel
diode, the Disconnect Diodes are switched back on, and the
Miller Runup resets to form the retrace or falling portion of
the sawtooth. Following a short stabilization period, the
Sweep Generator is ready to repeat the sequence.
Operating Modes. The TRIGGER MODE switch provides
four ways to switch the Sweep Gating circuit so that the
sweep begins:
1. In NORM, the Sweep Gating circuit is switched by a
pulse from the Trigger Generator.
2. In SINGLE SWEEP, two pulses are required to start each
sweep. First, a pulse from the Reset circuit (originating at
the RESET pushbutton) resets the Lockout Multi. Then, after
reset, the Sweep Gating circuit can be switched by a pulse
from the Trigger Generator.
3. FREE RUN results in recurrent sweeps that are indepen-
dent of any triggering signal. The switching of the Lockout
Multi at the end of the holdoff period makes available
enough current to switch the tunnel diode in the Sweep Gat-
ing circuit.
4. The AUTO position is a combination of NORM and
FREE RUN. If there are no trigger pulses coming from the
Trigger Generator, the Auto Trigger Multi permits the sweep
gating circuit to “free run”. When a pulse comes from the
Trigger Generator, the Auto-Trigger Multi switches the
Sweep Gating circuit to the “normal” condition, but this first
trigger pulse does not start a sweep. If the first trigger pulse
is followed by a second within about 80 msec, the Sweep
Gating circuit switches and a sweep begins. If trigger pulses
continue to arrive every 80 msec or less, the Auto Trigger
Multi remains in the “normal” condition and each sweep is
a triggered sweep. Whenever the period between trigger
3-2
pulses exceeds 80 msec, the Auto Trigger Multi reverts to
the free-run condition until the next trigger pulse arrives.
Circuit operation in each of the modes is described in
the following paragraphs. While reading the discussion,
reference should be made to the Sweep Generator schematic
in Section 5.
NORM, Quiescent Gonditions. In the quiescent state,
that is, when the sweep generator is triggerable and is wait-
ing for a trigger pulse, the circuit conditions are as follows:
Q125 in the Lockout Multi is conducting and holds Q135
cut off. With Q135 cut off, the current flow through R143,
R144, and R145 is about 3.8ma, which is enough to bias
tunnel diode D143 close to the point where it will switch to
its high voltage state. With D143 in its low voltage state,
Q144 is cut off. Since no current is flowing through Q144,
its collector voltage is positive and forward biases Q154 and
Q164,. The conduction of Q154 forward biases Disconnect
diode D155 and provides turn on bias for VI61A in the Miller
Runup circuit. The conduction of V161A establishes the op-
erating point of cathode follower VI73A. Diode D161,
transistor Q164, and associated circuit elements form a
feedback loop with the Miller circuit which under quiescent
conditions clamps the sawtooth output bus at about +4 volts
to provide a stable, repeatable sawtooth starting voltage.
Since Q144 is cut off under quiescent conditions, its
collector voltage cuts off Q184. With Q184 cut off, its col-
lector voltage cuts off VI73B and Q194, permitting Q204
to conduct, blanking the crt and setting the voltage on the
+GATE OUT connector to zero.
NORM, Sweep Triggered. When a trigger pulse is
received from the Trigger Generator circuit, the trigger pulse
supplies enough additional current to make tunnel diode
D143 switch to its high voltage state. Once D143 switches
to its high voltage state, the 3.8 ma current supplied to it is
sufficient to keep it in its high voltage state when the trig-
ger pulse ends.
The switching of D143 to its high voltage state biases Q144
into conduction, its collector voltage goes in a negative
direction and cuts off Q154. When Q154 cuts off, the volt-
age on its collector goes negative and reverse biases Dis-
connect diode D155 but applies conduction bias to Q184.
Q184 conducts, removes the negative voltage from the grid
of V173B and at the same time biases Q194 into conduction.
V173B unblanks the crt; Q194 generates a negative-going
pulse whose positive going trailing edge can be used to
switch channels in a multi-trace vertical plug-in unit. Since
Q194 also cuts off Q204 at this time, the collector voltage of
Q204 goes positive and generates the +GATE OUT pulse.
The negative-going step from Q154 reverse biases Dis-
connect diode D155 as previously explained. When D155
cuts off, the current through Timing Resistor R160 does not
cease, but instead begins to charge Time Capacitor C160
(see Timing Switch schematic). As the timing capacitor
charges, the grid of VI161A goes negative. The tube ampli-
fies the change in grid voltage and the inverted and greatly
amplified change is applied to the grid of cathode follower
V173A, which in turn couples the positive going voltage
back to the timing capacitor and opposes the change in
grid voltage of VI61A. {The positive going voltage also
reverse biases D161 and cuts off Q164). This action persists
@

throughout the sawtooth period and limits the total change
of grid voltage of VI61A to less than 0.5 volt. Since the
voltage drop across the timing resistor is held nearly con-
stant, the current through the resistor is essentially a fixed
value. This fixed current flows into the timing capacitor,
producing a linearly increasing voltage (sawtooth) across the
capacitor. The rate of the sawtooth rise is a function of
the RC time constant of C160 and R160 and the voltage
applied. D155 is a special diode that exhibits very low
leakage under reverse-bias conditions. This characteristic
prevents the diode from effectively altering the timing
resistance value.
Since the rate of the sawtooth rise is a function of the RC
time and the voltage applied, decreasing the voltage across
the timing resistor decreases the current into the timing
capacitor and therefore decreases the sawtooth rate of rise.
The voltage across the timing resistor can be varied by
turning the VARIABLE front panel contro! (RI160W) shown on
the Timing Switch schematic. This control permits the opera-
tor to obtain uncalibrated sweep rates at least two and one
half times slower than the calibrated rates obtained with
the contro! set in the CALIB position.
The sawtooth signal at the cathode of V173A is applied to
the Horizontal Amplifier, and through R171 and D176 is
also applied to the Holdoff circuit. The rising sawtooth volt-
age charges Holdoff capacitor C175 A—F. A point is finally
reached where D179 is reverse biased and D178 is forward
biased. Forward biasing D178 permits the sawtooth voltage
to turn on Q135 in the Lockout Multi.
When Q135 conducts, it resets tunnel diode D143 to its
low voltage state, turns off Q144, and ends the sweep. At
this time the unblanking pulse and the +GATE OUT pulse
are also terminated since V173B and Q194 are cut off by
cutting off Ql44 and Q184.
The time duration of the trigger pulses from the Trigger
Generator, which switch D143 fo its high voltage state and
start the cycle of operation, wil! always be considerabley less
than the time duration of the sweep. However, once a
sweep-gating trigger pulse switches D143 to its high-voltage
state, additional trigger pulses can have no further effect on
the operation. The tunnel diode reverts to its low-voltage
state only when Q135 turns on.
The positive-going voltage step at the collector of Q144
that occurs when the Lockout Multi is switched and cuts
Q144 off at the end of the sweep turns on Q154, The con-
duction of Q154 forward biases disconnect diode D155.
Since the timing capacitor still holds the charge developed
during the sweep, D161 remains back-biased. The timing
capacitor begins to discharge through the current paths as-
sociated with R171 and R401. D161 does not conduct until
the charge on the timing capacitor is nearly depleted.
The removal of the charge from the timing capacitor forms
the retrace or falling portion of the output sawtooth. As the
cathode voltage of V173A falls, D176 becomes reverse
biased. During the sawtooth rise, holdoff capacitor C175
A—F charges through D176, but must now discharge through
the high resistance of R175, R177, and R179. Thus while the
timing capacitor discharges rapidly, restoring the Miller Run-
up circuit to quiescent conditions, the charge on the holdoff
capacitor reverse biases D179 and the Lockout Multi cannot
reset until the charge in the holdoff capacitor decreases.
@
Circuit Description—-Type 3B4
When the sweep ends and the voltage on the cathode of
VI73A returns to its quiescent level, the voltage at the wiper
arm of R173 is negative and reverse biases D178; D179 is
reverse biased by the charge on the holdoff capacitor, and
with both diodes non-conducting, Q135 remains in conduc-
tion. With Q315 conducting, D143 remains in its low voltage
state and the sweep generator cannot be triggered since
Q135 robs all the current from D143. Q135 remains in con-
duction until the charge on the holdoff capacitor is removed
by current through R175 and R177. When the charge de-
creases to the point where D179 becomes forward biased,
the negative going voltage is applied to the base of Q135
and causes the Lockout Multi to switch. Q125 becomes the
conducting transistor and cuts off Q135. The entire sweep
generator is now restored to quiescent conditions.
TRIGGERING LEVEL control R16B permits the operator to
vary slightly the time between the completion of a sweep
and the instant when the sweep generator again becomes
triggerable. As Q135 turns off at the end of holdoff time, a
very short but sometimes significant amount of time is re-
quired for the current through tunnel diode D143 to reach
its quiescent level. When the relationship between the sweep
rate and triggering frequency is such that the sweep gating
trigger pulse tends to trigger each new sweep while the
tunnel diode current is approaching the quiescent level, the
display may jitter horizontally. The operator can minimize
and often eliminate the jitter by slightly adjusting the TRIG-
GERING LEVEL control.
FREE RUN Mode. When the TRIGGER MODE switch is
set to FREE RUN, sweep gating tunnel diode D143 is con-
nected through L139, R116, and the TRIGGER MODE switch
to +125 volts. This current path provides approximately 2.2
ma, which added to the aprroximately 3.8 ma through R144
and R145 is enough to bias D143 to its high voltage state.
The high voltage state of D143 biases Q144 into conduction
and starts the sweep as in the normal mode. When the
sweep ramp voltage reaches the desired voltage, the Lock-
out Multi switches and Q135 robs all the current from D143,
which resets D143 to its low voltage state and ends the
sweep. At the end of holdoff time, the Lockout Multi resets
and Q135 is cut off. Again there is sufficient current to bias
D143 to its high voltage state, and a new sweep commences.
Thus the completion of one cycle of operation causes the
next to begin, and trigger pulses have no affect on the
overall operation.
AUTO Mode. AUTO mode of operation is a combination
of NORM and FREE RUN. If there are no trigger pulses
coming from the Trigger Generator, the Sweep Generator
and sweep gating tunnel diode D143 operate as if the TRIG-
GER MODE switch were in FREE RUN. The Auto Multi (Q105
and Q115) biases sweep gating tunnel diode D143 into its
high voltage state, initiating a sweep. When the sweep
reaches its peak value (as set by the SWEEP LENGTH con-
trol} the Lockout Multi switches and resets D143 to its low
voltage state. The resetting of D143 ends the sweep. At the
end of holdoff time, the Lockout Multi resets and again per-
mits D143 to switch to its high voltage state, again initiating
a sweep. The cycle repeats as long as no triggering signals
are being received,
The arrival of a trigger pulse from the Trigger Generator
switches the monostable Auto Multi to its unstable state,
making Q105 the conducting transistor, The conduction of
3-3

Circuit Description—Type 3B4
Q105 immediately removes the current through R115 from
D143. This biases D143 to 3.8 ma and the circuit operates as
if the TRIGGER MODE switch were in the NORM position.
The Auto Multi remains in its unstable state for approximate-
ly 80 milliseconds or less. If a second trigger pulse is re-
ceived during the time the Auto Multi is in its unstable mode,
it switches sweep gating diodes D143 via D141 and initiates
a sweep. This second trigger pulse also signals the Auto
Multi to stay in its unstable state for an additional 80 milli-
seconds, As long as incoming trigger pulses arrive at inter-
vals shorter than about 80 milliseconds, the sweep is trig-
gered and operates as if the TRIGGER MODE switch were
set to NORM. If the interval between incoming trigger
pulses is longer than 80 milliseconds, the Auto Multi has
time to return to its stable state, and the Sweep Generator
resumes free-run operation. For this reason, the AUTO mode
should not be used where the interval between trigger pulses
exceeds 80 milliseconds.
Since the arrival of just one trigger pulse does not start
a sweep, but merely removes the circuit from a free running
condition, it is probable that the trigger pulse which switches
the Auto Trigger Multi will arrive while a free-run intiated
sweep is in progress. In this case the Sweep Generator can-
not become triggerable until the end of the holdoff period
for the sweep in progress, but from then on, every sweep will
be a triggered sweep if the reptition rate of the incoming
trigger pulse is greater than about 20 pulses per second.
Whenever the period between trigger pulses exceeds 80
milliseconds, the Auto Trigger Multi reverts to its stable state
and C105 charges up. With C105 charged, enough current
is again available through R115 to switch D143 and free
run the Sweep Generator.
The Auto Trigger Mutli incidentally controls the circuit
which lights the single sweep READY and SWEEP TRIG'D
lamps. In both the AUTO and NORM modes, the switching
of the Auto Trigger Multi cuts off Q114. As the collector of
Q114 rises toward the +125 volt source, the voltage increase
lights the SWEEP TRIG’D lamp (B119).
SINGLE SWEEP Mode. As previously explained in the
NORM Mode discussion, the Lockout Multi switches when the
holdoff capacitor discharges after the retrace portion of the
sweep. After the holdoff capacitor discharges down to where
D179 becomes forward biased, the current through R175,
R177, R124, R126 and R127 applies cutoff bias to Q135.
However, in the SINGLE SWEEP mode of operation, R177
ig connected to +125 volts, which serves to keep D179
reverse biased at all times. As the TRIGGER MODE switch
is turned from NORM position to the SINGLE SWEEP posi-
tion, switching transients trigger the sweep. As the sweep
runs up, D178 becomes forward biased and makes Q135
the conducting transistor of the Lockout Multi. Since the
+125 volts connected to R177 keeps D179 reverse biased,
the Lockout Multi stays locked up with Q135 conducting.
The conduction of Q135 diverts all current from D143 so
that it cannot switch and start a sweep. To unlock the
Lockout Multi, if is necessary to press the PUSH TO RESET
switch (SW135]. Pressing the PUSH TO RESET switch ap-
plies —100 volts through R137 to C136. When the voltage
across C136 becomes great enough to fire neon bulb B135,
the current through B135 and R135 generates a negative
pulse which is coupled through C135 to the Base of Q135.
The negative pulse cuts off Q135 and switches the Lockout
Multi, With Q135 cut off, the current through R144 and
R145 arms D143 so that it will switch to its high state when-
ever a trigger pulse is applied. The current through Q125
forward biases Q114 and turns on the READY lamp. The
Sweep Generator will now deliver a single sweep upon the
application of a trigger pulse.
Horizontal Amplifier
The block diagram in Section 5 shows the basic arrange-
ment of the horizontal amplifier circuits. The input to the
Horizonte! Amplifier proper is taken from the output of
cathode follower V173A in the Miller Runup circuit. Normal-
ly, the signal input to the Horizontal Amplifier is the sweep
ramp voltage. However, when the TIME/DIV OR HORI-
ZONTAL VOLTS/DIV switch is set to the EXT HORIZ IN
position, the signal on the grid of V173A is taken from the
External Horizontal Amplifier consisting of V161B and Q234.
As shown on the Sweep Generator schematic, the high
impedance EXT HORIZ IN input is applied to cathode fol-
lower V161B which in turn drives common base amplifier
Q234. Coupling between the input cathode follower and
the common base stage is by means of a resistor string
which includes the EXT HORIZ GAIN and VARIABLE con-
trols. The EXT HORIZ GAIN contro! is a screwdriver ad-
justable control that is set during calibration. The VARIABLE
control is an uncalibrated front panel control that permits
the operator to decrease the sensitivity of any of the five
SEC OR EXT VOLTS steps over a range from 1:1 to = 2.5:1.
Referring to the Horizontal Amplifier schematic in Section
5, the input from the Miller Runup cathode follower is applied
through
R401, R402, and D411 to the base of input transistor
Q414. SWP CAL contro! R402 provides a means of adjusting
the amount of signal drive to the Horizontal Amplifier. Front
panel FINE and POSITION controls apply de voltages to
the base of Q414, which in turn establishes the operating
points of the transistors in the output stages of the Hori-
zontal Amplifier. (Changing the de level around which the
transistors operate changes the position of the sweep on the
crt screen.) Diodes D413, D414, and D415 protect Q414 from
excessively large signals when externally generated hori-
zontal input signals are used.
The output of Q414 is applied to the input of a paraphase
amplifier consisting of Q424, Q434, Q423, Q433, and as-
sociated circuit elements. The two transistors in each side of
the paraphase amplifier are compound connected to achieve
the high effective gain needed to make the stage gain
dependent only upon the coupling resistors between the two
sides of the paraphase. The coupling network between the
two sides of the paraphase include the SWP MAG REGIS
resistor R422, the X50 MAG GAIN resistor R447, and the
MAG resistors R340A to R340R. The coupling resistance
value is about 9202 when no magnification is used (X1}
and is decreased to about 202 for X50 magnification (see
Magnifier Switch Schematic].
The output of the paraphase amplifier drives the cathodes
of a grounded-grid, push-pull connected twin triode (V444A
and V444B). The push-pull output of the twin triode is ap-
plied through pins 17 and 21 of the interconnecting plug to
the horizontal deflection plates of the crt.

SECTION 4
MAINTENANCE AND CALIBRATION
PREVENTIVE MAINTENANCE
Cleaning. Cleaning should precede calibration since the
cleaning process could alter the setting of certain calibration
controls.
Clean the instrument by vacuum and/or dry, low-pressure
compressed air (high velocity air could damage certain com-
ponents). Hardened dirt may be removed with a dry, soft
paint brush, cotton-tipped swab, or a cloth dampened with
water and a mild detergent solution (such as Kelite or Spray
White}. Abrasive cleaners should not be used. Pay special
attention to high-voltage circuits where conductive dust may
create leakage paths.
Lubrication. The contacts on the plug-in interconnecting
jack and plug should be lightly lubricated with an oil of the
type used on switch contacts. To extend the life of the con-
tacts, clean and relubricate if the oi! becomes contaminated
with abrasive dust. Keep a very light coating of grease
{Beacon No. 325 or equivalent) on the rotary-switch detents.
Visual Inspection. After cleaning, the instrument should
be carefully inspected for such defects as poor connections,
broken or damaged ceramic terminal strips, improperly
seated tubes or transistors, and heat damaged parts, The
remedy for most visible defects is obvious; however, over-
heating is only a symptom of unseen defects or improper
operation, and unless the cause of overheating is determined
before parts are replaced, the damage may be repeated.
Tube and Transistor Checks. Periodic preventive mainten-
ance checks on the tubes and transistors used in the instru-
ment are not recommended. The circuits within the instru-
ment generally provide the most satisfactory means of check-
ing tube or transistor performance. Performance of the cir-
cuits is thoroughly checked during recalibration so that
substandard tubes and transistors will usually be detected
at this time.
Recalibration. To insure accurate measurements, the in-
strument calibration should be checked after each 500 hours
of operation or every six months if used intermittently. Com-
plete calibration instructions are contained later in this sec-
tron.
The calibration procedure is helpful in isolating major
troubles in the instrument. Moreover, minor troubles not
apparent during regular operation may be revealed and
corrected during calibration.
CORRECTIVE MAINTENANCE
General Information. Certain parts in the instrument are
most easily replaced if definite procedures are followed as
outlined in the following paragraphs.
Many electrical components are mounted in a particular
way to reduce or control stray capacitance and inductance.
When selecting replacement parts, it is important to remem-
®
ber that the physical size and shape of a component may af-
fect its performance at high frequencies. After repair, por-
tions of the instrument may require recalibration.
Soldering. Special silver-bearing solder is used to estab-
lish a bond to the ceramic terminal strips in Tektronix instru-
ments. This bond may be broken by repeated use of ordinary
tin-lead solder or by excessive heating. We recommend
solder containing about 3% silver. Silver-bearing solder is
usually available locally or may purchased in one-pound
rolls through your Tektronix Field Engineer or Field Office.
Order by part number 251-514,
Because of the shape of the ceramic-strip terminals it is
recommended that a soldering iron with a wedge-shaped
tip be used. A wedge-shaped tip allows the heat to be con-
centrated on the solder in the terminals and reduces the
amount of heat required. It is important to use as little heat
as possible while producing a full-flow joint.
The following procedure is recommended for removing or
replacing components mounted on ceramic strips:
1, Use a 50- to 75-watt soldering iron.
2. Maintain a clean tip, properly tinned with solder con-
taining about 3% silver.
3. Use long-nose pliers for a heat sink. Attach pliers be-
tween the component and the point where heat is applied.
4. Apply heat directly to the solder in the terminal without
touching the ceramic. Do not twist the iron in the notch as
this may chip or break the ceramic strip.
5. Apply only enough heat to make the solder flow freely.
6. Do not attempt to fill the notch on the strip with solder;
instead apply only enough solder to cover the wires
adequately and form a small fillet on the wire. Overtilling
the notches may result in cracked terminal strips. If the
lead extends beyond the solder joint, clip the excess as
close to the joint as possible. Remove all wire clippings
from the chassis.
Standard Parts. Many components in the instrument are
standard electronic parts available locally. However, all
parts can be obtained through your Tektronix Field Engineer
or Field Office. Before purchasing or ordering, consult the
Parts List (Section 5) to determine the value, tolerance, and
ratings required.
Special Parts. Some parts are manufactured or selected
by Tektronix to satisfy particular requirements, or are manv-
factured for Tektronix to our specifications. These and most
mechanical parts should be ordered directly from Tektronix
Field Engineer or Field Office. See “Parts Ordering Informa-
tion” and “Special Notes and Symbols’ on the first page of
Section 5.
Ceramic Strip Replacement. Unsolder all connections,
then use a 34” diameter by 3” long plastic or hardwood
4-1

Maintenance and Calibration—Type 3B4
dowel and a small (2 to 4 0z.} mallet to knock the stud pins
out
of the chassis. Place one end of the dowel on the end
of the stud pin protruding through the chassis and rap the
opposite end of the dowel smartly with the mallet. When
both studs of the strip to be removed have been loosened in
this fashion, the strip is removed as a unit. The spacers will
probably come out with the studs. If not, they can be pulled
out separately. An alternate method of removing the termi-
nal strip is to use diagonal cutters to cut off the side of the
stud that holds the ceramic strip. The ceramic strip is re-
moved and the studs pulled from the chassis with a pair of
pliers, Replacement ceramic strips are supplied with studs
and spacers and the old studs need not be salvaged.
When the damaged strip and stud assembly has been
removed, place new spacers in the holes in the chassis. Using
the mallet and dowel, tap the new stud pins down thorough-
ly in the spacers. Be sure that these pins are driven com-
pletely through the spacers. You may wish fo cut off any
portion of the stud pin that protrudes through the spacers
with a pair of diagonal cutters. Fig. 4-1 shows how the
parts of the ceramic terminal strip fit together.
Fig. 4-1. Ceramic strip assembly.
Switch Replacement. Individual wafers normally are not
replaced in switch assemblies. Relpacement switches may
be ordered from Tektronix either unwired or with the as-
sociated wires and components attached. See Parts List, Sec-
tion 5.
When soldering leads to a switch, do not let solder flow
around and beyond the terminal rivet as this may destroy
the contact spring tension.
Troubleshooting Techniques. If the instrument is not
operating, attempt to isolate the trouble by a quick opera-
tional and visual check. Make sure that any apperent trouble
is actually due to a malfunction within the Type 3B4 and
not to improper control settings or to a fault elsewhere in the
oscilloscope system. Instructions for the operation of the
Type 3B4 are contained in Section 2 of this manual. (Opera-
ing instructions for the other components of the oscillo-
scope system will be found in the instruction manuals for
the individual components.)
Check the settings of all controls on the Type 3B4 and on
the associated components of the oscilloscope system. A
control set to the wrong position may cause what appears
to be a trouble symptom. Operate the controls to see what
effect, if any, they have on the trouble symptom. The normal
or abnormal operation of each particular control helps in
4-2
establishing the nature of the trouble. If a spare Type 3B4
is available, substitute the spare for the suspect unit and
check for proper operation of the oscilloscope system. This
is the best way to determine if the trouble is definitely in
the Type 3B4.
If spare Type 3B4 units are not available, and the trouble
symptoms are not definite, check the resistances at the pins
of the interconnecting plug. Table 4-1 lists the normal resist-
ances to ground for each pin. Typical voltages at various
points inside the Type 3B4 and significant waveforms are
shown on the various schematics in Section 5. The voltages
shown may vary slightly from instrument to instrument.
TABLE 4-1
Interconnecting plug resistances to ground.
Terminal Resistance Use
Number {to Ground | ee 7
1 80 © 6.3 AC
a) 802 63AC
37 Inf Unused
4 5K to 20K! | Multi trace sync pulse 7
5 02 GND oo
6 215K +300 V unregulated supply
7 | inf “Unused
8 Inf ~ Unused
9 00 GND
~~ 10 | ~~ 20K 7 + 300V supply oe
“af Inf t~<~=Sstsi‘é™S” Ose
12 1 meg? Int trigger signal?
13 | 10K to 20K' | Unblanking pulse ——
14 48K to 9.5K' | +125V supply -
“15 | 48K to 9.5K' | +125V supply
1 | 502 | ~12.2V supply
7 | a7 KE Output
“18 60 K Sawtooth drive
~ 49 fF OQ “GND
20 7K to 11.5K' | +125V unregulated supply
271d] KT COE”~”:C tpt
2 | oa | GND
23 | 85K to 11K' | —100V supply
24 | Inf | Unused
‘These readings depend upon the polarity of the meter leads and
in some cases upon the resistance range used.
* Trigger COUPLING switch must be set to DC.
All readings taken with a 20,000 02/v multimeter.
All wiring used in the Type 3B4 is color coded to facilitate
circuit tracing, In addition, all regulated power-supply
leads are coded with specific color combinations for easy
identification. In general, three stripes are placed on the
wires which supply regulated power. The code used is
the standard EIA number-color code. The first color (widest
stripe) indicates the first number of the voltage on that lead.
The second color indicates the second number of the lead
voltage, and the third color is a multiplier. The method is
similar to that used in color coding resistors. Thus, the +100-
@2
os
—

volt leads are coded brown, black, brown. The voltage is
positive if the body color of the wire is white and negative
if the body color of the wire is tan.
Most troubles that occur in Tektronix instruments result
from the failure of vacuum tubes or semiconductors. Once
the trouble has been isolated to a particular area or circuit,
check the tubes and semiconductors in the trouble area.
* Remember that when tubes or semiconductors fail, associated
circuit componts can be damaged.
Tube or transistor tester checks on the tubes or transistors
used in the Type 3B4 are not recommended. Testers may
indicate a tube or transistor to be defective when it is op-
erating satisfactorily in a circuit, or may fail to indicate
tube or transistor defects which affect the performance of
the circuits. It is recommended that tubes and transistors
be checked by substitution. If the tube or transistor is good,
return it to its socket, Unnecessary replacement of tubes or
transistors is not only expensive but may also result in need-
less recalibration of the instrument.
CALIBRATION AND VERIFICATION
Recalibrate the Type 3B4 after each 500 hours of opera-
tion, or every six months if used intermittently. It may also be
necessary to recalibrate certain sections of the instrument
when tubes, transistors, or other components are replaced.
Do not preset the internal adjustments. Presetting internal
adjustments makes it necessary to completely recalibrate the
instrument. :
The following portion of this manual presents a calibra-
tion and verification procedure. The title of each numbered
step begins either with ‘Adjust’ or ‘Check’, thereby identify-
ing the step function as calibration or verification. The steps
are identified in this manner because any or all groups of
numbered ‘Checks’ can be skipped without disrupting the
continuity of the procedure. However, all adjustments must
be completed in the order given and none should be skipped.
Remember that proper overall operation is assured only when
all steps in the procedure have been completed and ail ad-
justments have been made as accurately as possible.
Steps 14, 15, 17, 21 and 26 may be used as an abridged
adjustment procedure for adjusting all internal calibration
potentiometers and sweep calibration capacitors.
NOTE
The performance standards described in this sec-
tion of the manual are provided strictly as guides
to calibration of the Type 3B4 and should not be
construed as advertised performance specifications.
However, if the Type 3B4 performs within the
guide tolerances given in the calibration proce-
dure, it will also perform as listed in the Charac-
teristic section of this manual.
Equipment Required
1. Oscilloscope such as the Tektronix Type 561A. This
procedure assumes that the power supply voltages in the
oscilloscope are correct.
2. Tektronix 3-Series vertical plug-in unit such as the 3A].
This unit should be calibrated and operating in all respects.
@!
Maintenance and Calibration—Type 3B4
3. Audio oscillator with output frequencies from 30 cps to
30 ke, 30 volts amplitude.
4, Constant-amplitude sine-wave generator such as the
Tektronix Type 190A or 190B. Required characteristics: (a)
output frequencies from 50 ke to 20 mc, (b) output voltage
variable from about 0.3 volt to 4.0 volts peak-to-peak when
terminated in 500, and (c) provisions for maintaining con-
stant amplitude (manually or automatically) with a change
in frequency.
5. Time-mark generator such as the Tektronix Type 180A.
Markers required at 1 and 5 sec; 100, 50, 10, and 1 msec;
100, 50, 10, 5, and 1 psec; 5, 10, and 50 mc sine wave. All
outputs should have a time accuracy of at least 0.1%.
6. Three 5002 coax cables with BNC type connectors
(Tektronix Part No. 012-057).
7. Tektronix 50Q BNC termination Part No, 011-049, 2
required.
8. UHF-BNC adapter, for connecting the Type 190A or
190B to the BNC termination (UG-255/U).
9, Plug-in extension, Tektronix Part No. 013-034,
1. Check Multi-Trace Operation
Set:
3Al1 Controls Setting
CH 1
VOLTS/DIV 0.1
VARIABLE CALIB
POSITION Centered
AC DC GND GND
MODE ALTER
CH 2
VOLTS/DIV 0.05
VARIABLE CALIB
POSITION Centered
AC DC GND GND
3B4 Controls Setting
TRIGGER MODE FREE RUN
POSITION Centered
Procedure:
Rotate the Type 561A INTENSITY control clockwise until
the two traces appear. Set the Type 561A FOCUS control
for minimum trace width. Rotate the Type 3B4 TIME/DIV
switch through all sweep rates and check for 2 traces in
each position.
2. Check TRIGGERING LEVEL Control Zero Set
Set:
3A1 Controls Setting
MODE CH 1
All other controls unchanged
4-3

Maintenance and Calibration—Type 3B4
Fig. 4-2, Location of R12 and R13.
Procedure:
Remove the Type 3B4 from the Type 561A oscilloscope.
Connect the Type 3B4 to the Type 561A by means of the
plug-in extension (Tektronix part number 013-034), Connect
the voltmeter positive lead to the junction of R12 and R13
(see Fig. 4-2) in the Type 3B4, Adjust the Type 3B4 TRIG-
GERING LEVEL for a reading of zero volts on the voltmeter.
The knob index dot on the TRIGGERING LEVEL should be
positioned at the front panel 0 when the voltmeter reads
zero volts. If the control knob reads other than 0, loosen
the set screw holding the control knob to the TRIGGERING
LEVEL potentiometer, Return the knob index dot to the
front panel 0 without changing the TRIGGERING LEVEL
potentiometer. Check that the voltmeter continues to read
zero, Tighten the TRIGGERING LEVEL knob set screw. Check
that the voltmeter reads zero volts when the knob index
dot is set at the front panel 0 position,
Reinstall the Type 3B4 in the oscilloscope.
3. Check Low Frequency Trigger Response
Set:
3A1 Controls Setting
AC DC GND AC
All Others Unchanged
384 Controls Setting
TIME/DIV 10 »SEC
TRIGGER MODE FREE RUN
SOURCE EXT
COUPLING AC
4-4
Procedure:
Obtain a trace on the ert.
Connect a BNC "T" connector to the Type 3B4 EXT TRIG
IN connector,
Connect a coax cable from the audio oscillator to the BNC
“T" connector,
Connect a coax cable from the remaining side of the BNC
“T" connector to the Type 3A] CH 1 input.
Adjust the audio oscillator for 5 major divisions of de-
flection (500 mv) at 30 cycles.
Change the Type 3B4 TIME/DIV switch to 10 mSEC,
Change the Type 3B4 TRIGGER MODE switch to NORM.
Using the TRIGGERING LEVEL control, check for proper
external triggering {both AC and DC COUPLING and +
and — SLOPE} with a 500 millivolt, 30 cycle input signal,
Check to see that the setting of the TRIGGERING LEVEL
control is on the + side of O for a triggered waveform of
+ SLOPE and on the — side of 0 for a waveform of —
SLOPE.
Change the COUPLING switch to AC LF REJ, It should
not be possible to trigger the Type 3B4 on a 500-millivolt
30 cycle signal in the AC LF REJ position of the COUPLING
switch,
4. Check EXT + 10 Position of the SOURCE
switch
Set:
3A1 Controls Setting
CH 1 VOLTS/DIV 1.0
3B4 Controls Setting
SOURCE Switch EXT + 10
Procedure:
Adjust the Audio Oscillator for 5 major divisions of de-
flection (5 volts) of 30 cycle signal.
Repeat Step 3 using the new value of input voltage.
5. Check Internal Low Frequency Triggering
Set:
3B4 Controls Setting
SOURCE Switch INT
Procedure:
Set the audio oscillator output to give 0.5 miner division
of deflection of 30 cycle signal.
Repeat Step 3 using this new setting of the SOURCE
switch and audio oscillator output.
6. Check External Triggering Level Range
Set:
3A1 Controls Setting
CH 1 VOLTS/DIV 10
@i