Tektronix 221 User manual

TEKTRONIX
OSCILLOSCOPE
SERVICE
INSTRUCTION MANUAL
Tektronix, Inc.
P.O. Box 500
Beaverton, Ore on 97005
070-1573-01

WARRANTY
All TEKTRONIX instruments are warranted a ainst
defective materials and workmanship for one year. Any
questions with respect to the warranty should be taken up
with your TEKTRONIX Field En ineer or representative.
All requests for repairs and replacement parts should be
directed to the TEKTRONIX Field Office or representative
in your area. This will assure you the fastest possible
service. Please include the instrument Type Number or Part
Number and Serial Number with all requests for parts or
service.
Specifications and price c
. % & & * & '** * * *
Copyri ht 1973, new material 1974, by Tektronix,
Inc., Beaverton, Ore on. Printed in the United States of
America. All ri hts reserved. Contents of this publication
may not be reproduced in any form without permission of
Tektronix, Inc.
U.S.A. and forei n TEKTRONIX products covered by U.S.
and forei n patents and/or patents pendin .
TEKTRONIX is a re istered trademark of Tektronix, Inc.
http://m Q nom Qn .sqhill.co m

221 Service
T BLE OF CONTENTS
SECTION 1 OPERATING INFORMATION
AND SPECIFICATIONS Pa e SECTION 5 CALIBRATION (cont)
PRELIMINARY PROCEDURE
Pa e
5-2
INTRODUCTION 1-1 PRELIMINARY CONTROL
ELECTRICAL 1-1 SETTINGS 5-2
Vertical Deflection System 1-1 INDEX TO CALIBRATION
Tri erin 1-1 PROCEDURE 5-3
Horizontal Deflection System 1-2 POWER SUPPLY 5-4
Display 1-2 DISPLAY 5-6
Power 1-2 VERTICAL SYSTEM 5-7
PHYSICAL 1-3 SWEEP TRIGGER 5-11
HORIZONTAL SYSTEM 5-12
SECTION 2 FUNCTIONS OF CONTROLS
AND CONNECTORS 2-1 SECTION 6 TROUBLESHOOTING AIDS
SECTION 3 PREVENTIVE MAINTENANCE Dia rams 6-1
Troubleshootin Equipment 6-1
Disassembly 3-1 Component Color Codin 6-2
Cleanin 3-1 Isolatin Trouble To A Circuit 6-2
Visual Inspection 3-2
Semiconductor Checks 3-2
Recalibration 3-3 SECTION 7 CORRECTIVE MAINTENANCE
Obtainin Replacement Parts 7-1
SECTION 4 CIRCUIT DESCRIPTION Component Replacement 7-1
Recalibration After Repair 7-2
BLOCK DIAGRAM 4-1 Instrument Repacka in 7-2
CIRCUIT OPERATION 4-1
Vertical Amplifier 4-1 SECTION 8 ELECTRICAL PARTS LISTS 8-1
Tri er Sweep 4-3
Horizontal Amplifier 4-5
Power Supply 4-6 SECTION 9 DIAGRAMS, CIRCUIT BOARD
CRT Circuit 4-8 ILLUSTRATIONS
SECTION 5 CALIBRATION SECTION 10 MECHANICAL PARTS LISTS 10-1
TEKTRONIX FIELD SERVICE 5-1
TEST EQUIPMENT REQUIRED 5-1 CHANGE INFORMATION
REV. B, AUG. 1974

Fig. 1-1. The Tektronix 221 Oscilloscope.
221 Service
http://manoman.sqhill.com

OPER TING INFORM TION
ND SPECIFIC TIONS
Section 1—221 Service
INTRODUCTION
The 221 Oscilloscope is a sin le-channel, five me ahertz
portable instrument usin all solid state and inte rated
circuit components (except the crt). The instrument is
mechanically constructed to withstand the shock, vibration,
and other extremes associated with portability.
The dc to five me ahertz vertical system provides verti
cal deflection factors from five millivolts to 100 volts/
division at the tip of the inte ral hi h-impedance probe.
The tri er circuit provides stable tri erin over the full
ran e of vertical frequency response.
The horizontal deflection system provides calibrated
sweep rates from 200 milliseconds to one microsecond/
division. A sweep variable decreases calibrated sweep rates
by about 2.5:1, resultin in a minimum uncalibrated sweep
rate of about 0.5 second/division. A calibrated X10 sweep
ma nifier increases the sweep to at least 0.1 microsecond/
division. In addition, horizontal amplifier operation pro
vides a horizontal deflection factor of one volt/division for
X-Y operation. The cathode-ray tube has a six by ten
division raticule (each division equals approximately
0.2 inch).
The 221 is operated either from ac line volta e or from
internal rechar eable batteries. The internal batteries are
rechar ed from the ac power line by the inte ral battery
char er (with the instrument on or off).
This instrument will meet the followin electrical char
acteristics after complete instrument calibration. These
characteristics apply over an ambient temperature ran e of
—15°C to +55°C (+5°F to +131°F) when battery operated,
or 0°C to +40°C (+32°F to +104°F) when the instrument is
connected to ac line volta e. Warmup time for iven
accuracies is five minutes.
ELECTRIC L
The 221 oscilloscope will meet the followin electrical
specifications after calibration. The check portion of the
calibration procedure provides a convenient method of
checkin instrument performance without makin internal
checks or adjustments.
The followin electrical characteristics apply over an
ambient temperature ran e of —15°C to +55°C (+5°F to
+131°F) battery operation, or 0°C to +40°C (32°F to
+104°F) for line volta e operation.
Vertical Deflection System
Calibrated Ran e: five millivolts to 100 volts/division in
14 steps.
Accuracy: within 3% with VAR VOLTS/DIV in CAL
detent position.
Uncalibrated VAR VOLTS/DIV ran e: Continuously
variable, 3:1 minimum.
Bandwidth (with six division reference): to at least
five me ahertz (—3 dB point), with VARIABLE VOLTS/
DIV in CAL position.
Step Response: 70 nanoseconds or less.
Aberrations: +5%, —5%, 5% peak to peak total.
Input Resistance: 1 me ohm.
Input Capacitance: Approximately 29 picofarads.
Maximum Safe Input Volta e: 600 volts (dc + peak ac),
600 volts peak-to-peak ac.
Triggering
Tri er Sensitivity:
INT: 0.5 divisions from two hertz to one me ahertz,
increasin to 1 division at five me ahertz.
EXT: 0.5 volt from dc to one me ahertz; increasin
to 1 volt at 5 me ahertz.
AUTO PRESET: Tri ered at preset level on positive
slope of waveform.
Display Jitter: 20 nanoseconds or less.
EXT TRIGGER:
Input Resistance: Approximately one me ohm.
Input Capacitance: Approximately 30 picofarads.
Maximum Usable Input Volta e: Three volts (dc +
peak ac), six volts peak-to-peak ac (five me ahertz of less).
REV. B, FEB. 1976 1-1

Operating Information and Specifications—221 Service
Horizontal Deflection System
Sweep Generator:
Calibrated Ran e; 200 milliseconds to one microsecond/
division in 17 steps.
Accuracy (over center ei ht divisions): Within 3% with
VAR SEC/DIV in the CAL position.
Linearity (any two division portion, within the center
ei ht divisions): Within 3%, disre ard first 1 microsecond
of sweep.
SEC/DIV VAR (Variable): Continuously variable
between calibrated settin of the SEC/DIV switch. Extends
minimum sweep rate to approximately 0.5 s/div. Each
sweep rate is decreased 2.5:1.
Horizontal Ma nifier (HORIZ-MAG 10X) Calibrated
ma nifier when SEC/DIV is in CAL detent. Accuracy
within 5%, disre ard the first 1 microsecond of the
sweep.
External Horizontal Input:
Deflection Factor: One volt/div IX, 0.1 volt/div 10X.
Accuracy within 10%.
Bandwidth: With six division reference dc to
500 kilohertz.
Input Resistance: Approximately 500 kilohms.
Input Capacitance Approximately 30 picofarads.
Maximum Safe Input Volta e: 200 volts (dc to peak ac),
200 volts peak-to-peak ac.
Maximum Usable Input Volta e: Approximately
± nine volts.
Display
Graticule:
Type: Internal back line, non-illuminated.
Area: Six vertical divisions by 10 horizontal divisions.
Phosphor: P31 Standard.
Power
Line Volta e Operation:
Line Volta e Ran e: 90 V to 250 V ac; 80 V to 250 V dc.
Line Frequency Ran e: 48 to 62 Hertz.
Maximum Power: Five watts.
Line Fuse: 0.2 A 250 V.
Common Isolation:
Line Operation: Line volta e plus floatin volta e not
reater than 250 volts RMS sine wave, or 1.4 times line
volta e + dc + peak ac floatin volta e not reater than
350 volts.
Battery Operation: Common to outside of case
floatin volta e not reater than 500 volts RMS or
700 volts dc + peak ac.
Battery Operation:
Batteries: Ten rechar eable A nickel-cadmium cells.
Char e time: 16 hours for full char e.
Battery Char e Indicator- Battery meter indicates Full,
Low and Rechar e. Rechar e is indicated after automatic
shut-off turns instrument off.
Battery Dischar e Char e Protection: Instrument opera
tion automatically interrupted when battery char e is less
than 10 volts.
Typical Operatin Time (after full char e cycle at +20°C
to +30°C): Two to three hours. Lon est operatin time
provided at low trace intensity.
Typical Char e Capacity
(Referenced to char e/dischar e at +20°C to +30°C):
T BLE 1-1
CH RGE OPER TING TEMPER TURE
TEMPER TURE +15°C +20° C to +30° C +55° C
0°C (+32° F) 40% 60% 50%
+20° C to +30° C 65% 100% 85%
(+68° F to +86° F)
40° C (+104°F) 40% 65% 55%
1-2 REV. B, FEB. 1976

Operating Information and Specifications—221 Service
PHYSIC L
Temperature:
Operatin from Batteries, -15°C to +55°C (+5°F to
+131°F).
Char in or operatin from ac line, 0°C to +40°C
(+32°F to +104°F).
Stora e, -40°C to +60°C (-40°F to +140°F).
Humidity (operatin and non-operatin ): 5 days 50°C to
95% relative humidity.
Shock (operatin and non-operatin ): Tested with two
shocks at 100 , one-half sine, two millisecond duration
each direction alon three major axes.
Wei ht (without accessories):
3.5 pounds (1.5 kilo rams)
Altitude:
Operatin , to 25,000 feet (maximum operatin tem
perature decreased by 1°C per 1,000 feet shown above
15,000 feet).
Dimensions (measured at maximum points):
Hei ht: 3.0 inches (7.6 centimeters).
Width: 5.25 inches (13.2 centimeters).
Non-operatin , to 50,000 feet. Depth: 9.0 inches (22.8 centimeters).
REV. APR 1974 1-3

FUNCTIONS OF
CONTROLS ND CONNECTORS
Section 2—221 Service
All controls and connectors necessary for operation of
the 221 are located on the ri ht side panel of the
instrument. See Fi . 2-1. A brief description of each control
and connector is iven here.
VOLTS/DIV—selects vertical deflection factor (VAR
VOLTS/DIV must be in the CAL position for indicated
deflection).
STEP ATTEN BAL—screwdriver adjustment to balance
the vertical system for minimum trace shift when chan in
deflection factors.
Vertical POS—controls the vertical position of the trace.
VERT GAIN—screwdriver adjustment to set the ain of
the vertical system.
VAR VOLTS/DIV—provides a continuously variable
deflection factor between the calibrated settin s of the
VOLTS/DIV switch.
INPUT COUPLING—selects method used to couple the
input si nal to the vertical amplifier system.
AC—blocks dc components of input si nal. Low
frequency limit (—3 dB point) is about two hertz.
GND—Input circuit is rounded. The applied si nal is
connected to round throu h a lar e resistor to provide a
prechar e path for the AC input couplin capacitor.
DC—All components of the input si nal are passed to the
vertical amplifier system.
SEC/DIV selects the sweep rate (VAR SEC/DIV must be
in the CAL detent; HORIZ MAG must be in XI position,
for indicated sweep rate). 1 V position allows for X-Y
operation with the horizontal deflection provided by the
si nal connected to the EXT TRIG OR HORIZ INPUT
jack.
Horizontal POS—controls the horizontal position of the
trace.
VAR SEC/DIV—provides continuously variable sweep
rates between calibrated settin s of the SEC/DIV switch.
Extends the minimum sweep rate to about
0.5 second/division.
HORIZ MAG—X10 ma nifier to increase the maximum
sweep time to 0.1 microsecond/division and provides a
horizontal sensitivity of 0.1 volt/division in X-Y operation.
Fig. 2-1 Side panel showing controls and connectors.
REV. B, FEB. 1977 2-1

Functions of Controls nd Connectors—221 Service
VOLTS/DIV
Fig. 2-2. Side panel showing controls and connectors.
SWP CAL—screwdriver adjustment to set the basic
timin of the horizontal system.
TRACE ROTATION—screwdriver adjustment to ali n
trace with raticule lines.
EXT TRIG OR HORIZ INPUT—banana jack for input of
an external tri er si nal or for input of an external
horizontal (X) si nal for X-Y operation.
LEVEL/SLOPE—selects the amplitude point and slope
of the tri er si nal on which the sweep is tri ered. When
the indicator dot is to the left of center, the sweep is
tri ered on the positive- oin slope of the tri er si nal; to
the ri ht of center, on the ne ative- oin slope. When the
LEVEL/SLOPE control is set to the AUTO PRESET
detent, the sweep is automatically tri ered at a preset level
on the positive- oin slope.
AUTO PRESET—screwdriver adjustment to set the
PRESET tri er point for AUTO sweep operation.
EXT-INT—selects the source of the tri er si nal.
INTENSITY—controls bri htness of crt display (detent
turns OFF instrument power).
FOCUS—screwdriver adjustment to obtain a well-defined
display
BATTERY—expanded scale meter to indicate the
relative char e level of the internal batteries.
POWER—(counterclockwise detent of the INTENSITY
control). Controls power to the instrument. Does not
interrupt char in current to the internal batteries when
connected to an AC line volta e.
COMMON—banana jack to establish common round
between the 221 and the external si nal source or
equipment under test.
2-2 REV. B, FEB. 1977

Section 3—221 Service
PREVENTIVE M INTEN NCE
Preventive maintenance, when performed on a re ular
basis, can prevent instrument breakdown and may improve
the reliability of the 221. The severity of environment to
which this instrument is subjected will determine the
frequency of maintenance. A convenient time to perform
preventive maintenance is precedin recalibration of the
instrument.
Disassembly
To ain access to the interior of the instrument, unwind
the probe and the power cord from the rear of the
instrument. Remove the five screws in the bottom cover of
the instrument. See Fi . 3-1. Gently separate the bottom
cover from the instrument and lay aside.
If access to the front of the Input circuit board is
necessary, remove the knobs from all of the external
control shafts. Remove the two screws securin the side
panel to the Input circuit board and remove the instrument
side panel.
Cleaning
The 221 should be cleaned as often as operatin
conditions require. Accumulation of dirt in the instrument
can cause component breakdown.
The hi h impact plastic covers provide protection a ainst
dust in the interior of the instrument. Loose dust accu
mulated on these covers can be removed with a soft cloth
or small brush. The brush is also useful for dislod in dirt
on and around the side panel controls. Dirt that remains
can be removed with a soft cloth dampened in a mild
deter ent and water solution. Abrasive cleaners should not
be used.
Cleanin the interior should only be occasionally neces
sary. The best way to clean the interior is to blow off the
dust with a dry, low-velocity stream of air. A soft-bristle
brush or a cotton-tipped applicator is useful for cleanin in
narrow spaces or for cleanin more delicate components.
Avoid the use of chemical cleaning agents which
might damage the plastics used in this instrument.
Avoid chemicals which contain hydrochloric acid,
sodium hydroxide, or sulfuric acid.
REV. APR 1974 3-1

Preventive Maintenance—221 Service
Visual Inspection
The 221 should be inspected occasionally for such
defects as broken connections, improperly seated transis
tors, dama ed circuit boards, and heat-dama ed parts. The
corrective procedure for most visible defects is apparant;
however, particular care must be taken if heat-dama ed
components are found. Overheatin usually indicates other
trouble in the instrument; therefore, correctin the cause of
the overheatin is important to prevent recurrance of the
dama e.
Semiconductor Checks
Periodically checkin the semiconductors in the 221 is
not recommended. The best check of semiconductor
performance is actual operation in the instrument. If
checkin the performance of a semiconductor out of the
instrument is desired, a dynamic checker, such as the
Tektronix Type 577 Curve Tracer system, is recommended.
Lead confi urations of the semiconductors used in the 221
are shown in Fi . 3-2.
An extractin tool should be used to remove the
ei ht-pin flat inte rated circuit to prevent dama e to the
pins. If an extractin tool is not vailable when removin one
of these inte rated circuits, pull slowly and evenly on both
ends of the device. Avoid havin one end of the inte rated
circuit disen a e from the socket before the other, as the
pins may be dama ed. When replacin semiconductors, key
the semiconductor index with that of the socket. Failure to
do so will result in dama ed components.
Fig. 3-2. Lead configurations of the semiconductors used in the 221 Oscilloscope.
3-2 REV. APR 1974 ©l

Preventive Maintenance—221 Service
Recalibration
To ensure accurate measurements, check the calibration
of this instrument after each 1000 hours of operation, or
every six months if used infrequently. In addition, replace
ment of components may necessitate recalibration of the
affected circuits. The Calibration procedure can also be
helpful in localizin certain troubles in the instrument. In
some cases, minor troubles may be revealed or corrected by
recalibration.
3-3
//manom

Section 4—221 Service
CIRCUIT DESCRIPTION
The followin circuit description be ins with a discus
sion of the instrument usin theblockdia ram. Then each
circuit is described in detail, usin detailed dia rams
where necessary to show the relationship of each sta e
and the controls to that sta e. The block dia ram is shown
in Section 9.
BLOCK DI GR M
Si nals to be displayed on the crt are applied to the
probe tip. The si nal is then amplified by the vertical
amplifier. The vertical amplifier contains the vertical
position, attenuation, ain compensation, and input
couplin circuitry.
The Tri er Generator initiates the sweep si nal
produced by the sweep enerator. The input si nal to the
tri er enerator is selected from the vertical si nal or
from an external si nal applied to the EXT TRIG connec
tor.
The Sweep Generator circuit produces a linear saw
tooth si nal that is amplified by the Horizontal Amplifier
circuit. The slope of the sawtooth enerator is controlled
by the SEC/DIV switch. This circuit also produces the
unblankin si nal coincident with the sawtooth to permit
display presentation.
The power supply circuit provides all the volta e
necessary for the operation of the instrument. Input power
is provided by internal batteries or a line source. This
circuit also provides a rechar in circuit for the internal
batteries.
CIRCUIT OPER TION
The followin is a description of the electrical operation
and relationship of the circuits in the 221 with a descrip
tion of the circuitry most commonly used by Tektronix. If
more information is desired on the commonly used circuit,
refer to the followin textbooks:
Phillip Cutler, "Semiconductor Circuit Analysis",
McGraw-Hill, New York, 1964.
Vertical mplifier
The Vertical Amplifier circuit is divided into three
sections; the attenuators, the Preamplifier, and the Output
Amplifier. A block dia ram of the Vertical Amplifier is
shown in Fi . 4-1. Schematics of the Vertical Amplifier are
shown on dia rams 1 and 3.
The input si nals are applied to a 800 kilohm im
pedance in the probe and a 200 kilohm attenuator
network, which provides the 1 me ohm impedance for the
oscilloscope. The output of the attenuator is applied to the
input of the Preamplifier, which consists of three sections;
the buffer amplifier (Q132A and B, Q136A and B), a
resistive attenuator (R143-R156), and an operational
amplifier (Q162A and B, Q172A and B, and Q164). The
Preamp sta e also provides Probe compensation,
Attenuator compensations, Step Attenuator Balance,
Volts/Div Balance, and Vertical Step Response (C167).
Output si nals from the resistive attenuator are applied
to the positive input of the operational amplifier (Q162A
base). The output si nal (from collector Q164) is then
applied to both the input of the output amplifier (base
Q422A) and, throu h feedback network R166and R167,to
the ne ative input of the operational amplifier (base of
Q162B). Transistor Q172A and B serve as dc biasin
circuitry for these amplifiers.
The Output Amplifier provides the final amplification
for the crt deflection plates and consists of three amplifier
sta es. Transistors Q422A and B, Q426A and B, and Q424
are connected as an operational amplifier, with resistors
R416, R417, R418, and R432 servin as the feedback
network. It is otherwise similiar in operation to the
operational amplifier described for the Preamplifier sta e.
The operational amplifier drives a differential amplifier
(Q442A and B), which in turn drives a dual output
amplifier. The Output Amplifier sta e also provides the
circuitry for the bandwidth adjustment (C432), the VER
TICAL POSITION control (R413), the Vertical Gain con
trol (R417), and the VOLTS/DIV VARIABLE control
(R418). Transistor Q432 is connected as an emitter
follower and provides the internal tri er si nal for the
tri er circuitry.
REV. B, AUG 1974 4-1

Circuit Description—221 Service
Fig. 4-1. Simplified block diagram of the Vertical mplifier circuit.
One half of the dual output amplifier sta e is an
operational amplifier consistin of transistors Q452,
Q456, and diodes CR454-CR455, which provide the
amplification for the positive si nal to the crt vertical
deflection plate. Likewise, transistors Q464, Q466, and
diodes CR467-CR468 make up the other half of the
operational amplifier, which serves the same function for
the ne ative vertical deflection plate. Both amplifiers
operate the same, so only the positive si nal amplifier will
be explained.
Under normal si nal conditions, the volta e on the
positive deflection plate is maintained by the emitter
follower Q456. The output si nal from the differential
amplifier (collector Q442A) is applied to the input of the
operational amplifier (base Q452). Feedback resistor R456
receives a common output si nal from the collector of
Q452 and the emitter of Q456. Under fast, positive output
si nal conditions, the deflection plate is driven throu h
the emitter follower Q456. Under fast ne ative si nal
conditions the collector of Q452 oes ne ative, and turns
on a commutatin diode CR454, which turns off Q456
throu h diode CR455, and thereby allows the collector of
Q452 to drive the deflection plate.
Transistors Q452, Q456, Q464, and Q466 are specially
selected transistors for a low' Cob (0.3 pf max.), a
500 Me ahertz Ft and a Vet™ and Vcev not less than 80 volts.
The lead confi uration is B ECS with the emitter and shield
leads tied to ether on the printed circuit board.
4-2 REV B, AUG 1974
http://m Q n om an.sqhill.com

Circuit Description—221 Service
TRIGGER SOURCE
FOLLOWER
Fig. 4-2. Simplified block diagram of the Trigger Sweep circuit.
T rigger/Sweep
The Tri er Sweep circuit performs two functions. The
Tri er portion of the circuit derives tri er si nals
internally from the input of the vertical amplifier, or from
si nals applied to the EXT TRIG INPUT banana jack. The
tri er output si nals are coupled to the Sweep Multi
circuit, which starts the action of the Sweep circuit.
The Sweep portion of the circuit produces a linear
sawtooth output si nal when initiated by the Tri er
circuit. The output si nal is then amplified by the Horizon
tal Amplifier circuit for horizontal deflection of the crt. An
unblankin ate si nal is also developed that is coincident
with the sawtooth waveform. This ate si nal unblanks the
crt to permit a display presentation. An EXT HORIZ INPUT
is also provided so external si nals can be applied to the
Horizontal Amplifier circuit to produce horizontal deflec
tion for the crt. The block dia ram of the Tri er/Sweep
circuit is shown in Fi . 4-2. The schematic of the circuit is
shown on dia ram 2.
The Tri er Source Follower (Q232A, Q232B) receives
and buffers all incomin tri er si nals and couples them
to the base of Q234, one half of a differential amplifier
(Q234 and Q226). TRIGGER LEVEL/SLOPE control R213
sets a reference volta e level that corresponds to a desired
tri er point on the incomin si nal. This volta e is
coupled throu h Q212 to the base of Q226, the other half
of the differential amplifier. Transistor Q214 provides a
slope switchin function in conjunction with Tri er
Slope Selector transistors Q216 and Q218. When
TRIGGER LEVEL/SLOPE control R213 is rotated, the
resultin volta e applied to the base of Q222 causes it to
saturate at about the mid-point, or a zero volt level of the
control. At this point Q214 turns on and slope switchin
occurs throu h Q216 or Q218.
REV. B, AUG 1974 4-3

Circuit Description—221 Service
The output of the differential amplifier (Q226-Q234) is
coupled throu h emitter follower Q236 to the Schmitt
Tri er, composed of transistors Q244 and Q246. This
circuit controls the action of the Sweep Multi. When Q246
turns on, Tri erSlopetransistorsQ216 (—Slope) orQ218
(+Slope) will conduct. This couples the output throu h
T312, chan es CR317 to a hi h state, and enerates a
tri er pulse for the Sweep Multi. Diode CR317 returns to
the low state when Hold-off transistor Q312 becomes
turned off
The Sweep Multi circuit composed of transistors Q322,
Q324, and Q326 drives the Sweep Start transistors Q330
and Q334, which produce an unblankin si nal for the crt
and sets the sweep start volta e for the Miller Inte rator
When the sweep is tri ered, transistor Q322 is turned off
and Q324 turns on. Transistor Q332 then char es up
sweep hold-off capacitors C325, C326, and C327 Tran
sistor Q334 turns off Q328 and Q330. The Miller Inte rator
is composed of Q336A and B, Q338, Q340, and Q342.
Transistor Q316 is turned off and Q312 is turned on. This
resets CR317 to its low state, inhibitin any further tri er
pulses. The sweep is now set for the run-down. As the
sweep runs down, Q324 becomes turned off by the current
throu h CR328 and R328. When Q324 turns off, Q322
turns on. Transistor Q328 also turns on and supplies
retrace current throu h R333. The sweep runs back up
until Q330 turns on and sets the sweep start volta e. The
retrace current from the collector of Q330 then dischar es ,
the sweep start hold-off capacitors. When transistor Q316
turns on and Q312 off, the tri er pulses are no lon er
inhibited.
The Latch circuit composed of transistors Q252, Q254,
and emitter follower Q256, controls the Sweep Multi
operation in the Auto Preset position. The output of Q244
turns on the Latch transistors and dischar es C256, the
free-runnin hold-off capacitor, when S213B is in the
open position (Auto Preset mode). In the closed position,
S213B keeps C256 from bein char ed throu h resistor
R256, permittin tri er pulses to initiate the circuit
action. Emitter follower Q256 chan es CR317 to its hi h
state (in the absence of tri er pulses) throu h R258,
R316, and the secondary of T312.
In the EXT Sweep mode of operation, CR228 is
connected to —5 volts by S350, which turns off the tri er
amplifier. Transistor Q322 is turned off by R318 and
CR318, turnin on Q324 to unblank the crt. Transistor
Q328 is turned off, which turns off the retrace current,
permittin the Miller Inte rator to be connected as an
invertin operational amplifier
4-4 REV. B, AUG 1974

Circuit Description—221 Service
+ R545
I
| HOBIZ MAg]
S521
HORIZSIG
TO CRT
DEFLECTION
PLATES
Fig. 4-3. Simplified block diagram of the Horizontal Output mplifier circuit.
Horizontal mplifier
The Horizontal Output Amplifier provides amplification
for the sweep si nal or the horizontal si nal (used in theX-
Y mode), to drive the crt deflection plates. A block dia ram
of the Horizontal Output amplifier is shown in Fi . 4-3. The
schematic is shown on dia ram 3.
Transistor Q502 is connected as a buffer amplifier
between the sweep enerator and the horizontal amplifier.
The horizontal amplifer consists of three operational
amplifiers. Transistors Q516, Q522, and Q526 are con
nected as the first operational amplifier that controls the
horizontal ain, positionin , and ma nification.
Resistors R504 and R505 serve as the input resistance
to the amplifier. The feedback resistance (R525, CR525,
and R511) is connected from the emitter of Q526 back to
the operational amplifier input (emitter Q516), and deter
mines the ain for the XI and X10 mode. In the XI mode,
Q518 is turned on and shorts R511. In the XI0 mode, Q518
is turned off, addin R511 to the feedback resistance.
Horizontal Position control R518 applies an offset current
to the input of the operational amplifier for the required dc
positionin .
Current output from the collector of Q526, which is
proportional to the output si nal, is applied throu h the
diode limiter CR532, CR533, CR535, and CR536 to the
input of the second operational amplifier.
TransistorsQ532, Q542, and Q544 are connected as the
second operational amplifier, which drives the input
resistance (R548) of the third operational amplifier and the
positive deflection plate. Resistor R545 serves as the
amplifier feedback resistance, with R542 and C542
providin the Hi h Frequency si nal path for the positive
oin output si nal.
The third operational amplifier consists of transistors
Q552, Q554, and Q556, with R548 bein the input
resistance and R556 the feedback resistance. It is con
nected as an invertin amplifier with a ain of one, and
drives the ne ative deflection plate. This amplifier
operates similarly to the vertical deflection plate drivers
described in the Vertical Amplifier section.
REV. B, AUG 1974 4-5

Circuit Description—221 Service
BRIDGE
RECTIFIER
CR612
CR613
CR614
CR615
POWER INVERTER
RFI
FILTER
P610
LINE
INPUT
LINE
INVERTER
0622
Q626
T623
RECTIFIERS
T633
CR633
CR632
REGUL TOR
+5 -5 SECOND RY INVERTER
Gl
REFEF
f
U6
D
=IENCE
rfP
54
I ON
I
S738
+48 V
+76 V
Fig. 4-4. Simplified block diagram of the Power Supply circuit.
The circuit from the power line to the primary of
T633 is floating at line potential. Any signal
measurement in this circuit must be referenced to
pin 1 of T633, and should be measured only if an
Isolation transformer is used on the power line.
Power Supply
The 221 Power Supply circuit is divided into three
sections; the Power Inverter, the +5 V -5 V Re ulator, and
the HV Inverter. A block dia ram of the Power Supply is
shown on Fi . 4-4. The schematic of the Power Supply is
shown on dia ram 4.
When the instrument is connected to a power source,
C612, R612, C613, R613, R614, L610, and C614 function as
a RFI filter to minimize RFI interference. The line volta e is
rectified by diode brid e CR612, CR613, and CR615,
which supplies the dc volta e for the Line Inverter circuit.
Transistors Q622 and Q626 convert the dc volta e into a
square-wave volta e. The square-wave volta e is applied
to an LC resonant circuit consistin of C623 and T633.
Feedback is provided from T633, throu h R626, back to
the base drive transformer T623, to sustain the oscillation.
As the output power chan es, the frequency of the square-
wave chan es with respect to the resonance of L (T633)
and C (C623), permittin the Power Inverter to remain
constant. In this way a correct output level is maintanined
over the specified line volta e ran e and operatin
conditions.
4-6 REV. B, AUG 1974

Circuit Description—221 Service
The output of the Power Inverter is rectified by CR632
and CR633, filtered by L632-C632, and then used to power
the instrument and char e the batteries. Transistor Q634
is an error amplifier that re ulates the battery char e
current by providin a feedback si nal throu h current-
sensin resistor R632 back to the control windin of T623.
This windin (pins 6 throu h 9), varies the frequency of
the Power Inverter circuit. When the 221 is operated from
the battery source, CR634 serves to connect the power to
the instrument. When the 221 is connected to a power line,
diode CR634 becomes reversed biased, which permits the
error amplifier (Q634) to function. A start-up circuit
consistin of CR622, C622, and R622 injects a si nal into
the base of Q626 to start-up the Line Invertercircuit. Diode
CR621 serves to stop the free-runnin action of the start
up network.
The +5 V —5 V Re ulator circuit derives its volta e
from the Line Inverter circuit or the batteries, and
re ulates this volta e to 10 volts. Diodes CR654 and
VR654 serve as the reference source, with Q648 func
tionin as a series-pass element. Transistors Q642 and
Q644 operate as an error amplifier of the series-pass
re ulator circuit. Transistors Q640 and Q646 function as a
protective circuit for the battery supply. When the battery
volta e becomes lowerthan 10.3 volts, Q640and Q646are
turned off, which turns off the entire power supply. This
action prevents the complete dischar e of the batteries
whenever the battery char e becomes low.
Operational amplifier U654 is connected as a buffer
amplifier providin a round reference at the mid-point of
the 10 volt supply, creatin the +5 volt and the —5 volt
supplies. Capacitors C656 and C657 provide filterin for
the respective supply.
The Secondary Inverter circuit produces the +48 volt,
+75 volt, approximately 600 volt peak-to-peak supply,
and a 1.4 volt peak-to-peak crt heatersupply. The+48 volt
peak-to-peak supply is rectified and filtered by the
network consistin ofC712,CR712,CR713,and L713.The
+75 volt peak-to-peak supply is rectified and filtered by
the network consistin of C715, CR715, CR716, C714, and
L716. Transistors Q666 and Q668 are connected as a free-
runnin inverter, drivin T701. Transistors Q660 and
Q662, in conjunction with FET Q664, operate as a
re ulatin circuit for the 1000 volt supply in the Secon
dary Inverter sta e. When the 1000 volt supply is at a
normal level, Q664 supplies the base drive to Q666 and
Q668. When a chan e occurs in the 1000 volt supply, a
difference is sensed by the ate of Q664 {throu h
feedback resistor R667), which results in a re-adjustment
of the base drive to Q666 and Q668. An adjustable current
reference is also provided to Q664 throu h Q660and Q662
by HIGH VOLTAGE adjustment R662.
REV. B, AUG 1974 4-7

Circuit Description—221 Service
Fig. 4-5. Simplified block diagram of the CRT circuit.
CRT Circuit
The CRT circuit provides the hi h volta e and control
circuits necessary for operation of thecrt. A block dia ram
of the CRT circuit is shown in Fi . 4-5. A schematic is
shown on dia ram 5.
A network consistin of CR733, C733, CR734, C734,
CR735, and CR736 is connected as a volta e doubler that
provides approximately 1100 volts to the crt circuit. The
1100 volts is connected to a 110 V Zener diode VR738,
which provides a 1000 volts supply to the Intensity circuit.
It is further divided by R734 and R735to provide the Focus
control volta e. The 1000 volt supply is also returned to
the Secondary Inverter sta e and serves as a reference for
the re ulatin circuit.
Deflection plate blankin is used for controllin the crt
beam. When an unblankin si nal is received, Q754 turns
on and forward biases CR756, which lowers the deflection
blankin volta e to approximately 40 volts, which allows
the electron beam to pass to the crt screen. The CRT GRID
BIAS adjustment R739 controls the maximum usable
intensity. The TRACE ROTATION adjustment R751 con
trols the current throu h L751, which affects both the
vertical and horizontal rotation of the crt beam. FOCUS
control R733, used in conjunction with ASTIGMATISM
adjustmenet R752, is adjusted to obtain a well-defined
display. UNBLANKING adjustment R753 is adjusted for
optimum trace bri htness.
4-8 REV. B, AUG 1974