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TM 9-6625-1094-14-1
TECHNICAL MANUAL
OPERATOR'S, ORGANIZATIONAL, DIRECT SUPPORT, AND GENERAL SUPPORT MAINTENANCE MANUAL TIME BASE PLUG-IN TEKTRONIX TYPE 3B4
This copy is a reprint which includes current pages from Changes 1 and 2.
HEADQUARTERS, DEPARTMENT OF THE ARMY FEBRUARY 1972
TM 9-6625-1094-14-1
This manual is an authentication of the manufacturer's commercial literature which, through usage, has been found to cover the data required to operate and maintain this equipment. Since the manual was not prepared in accordance with military specifications, the format has not been structured to consider level of maintenance nor to include a formal section on depot overhaul standards. This manual contains copyrighted information that is printed with the permission of Tektronix, Inc. Beaverton, Oregon.
CHANGE No. 3
TM 9-6625-1094-14-1 Change 3 HEADQUARTERS DEPARTMENT OF THE ARMY WASHINGTON, DC, 14 August 1986
OPERATOR'S ORGANIZATIONAL, DIRECT SUPPORT AND GENERAL SUPPORT MAINTENANCE MANUAL, INCLUDING REPAIR PARTS AND SPECIAL TOOLS LIST: TIME BASE PLUG-IN TEKTRONIX TYPE 3B4 (NSN 4931-00-910-8226)
Current as of 16 April 1986
TM 9-6625-1094-14-1, 4 February 1972, is changed as follows: 1. Remove old pages and insert new pages as indicated below. New or changed material is indicated by a vertical bar in the margin of the page. Remove pages 0-1 7-1 through 7-11 Insert pages 0-1 7-1 through 7-15
2. File this change sheet in front of the publication for reference purposes.
By Order of the Secretary of the Army:
JOHN A. WICKHAM, JR. General, United States Army Chief of Staff Official:
R. L. DILWORTH Brigadier General, United States Army The Adjutant General Distribution: To be distributed in accordance with DA Form 12-34C, Block No. 319, requirements for calibration procedures publications.
TM 9-6625-1094-14-1 Change 2 CHANGE NO. 2 HEADQUARTERS DEPARTMENT OF THE ARMY WASHINGTON, D.C. 21 March 1975
OPERATOR'S, ORGANIZATIONAL, DIRECT SUPPORT, AND GENERAL SUPPORT MAINTENANCE MANUAL, INCLUDING REPAIR PARTS AND SPECIAL TOOLS LIST: TIME BASE PLUG-IN, TEKTRONIX TYPE 3B4 (NSN 4931-00-910-8226)
Current as of 11 September 1974
TM 9-6625-1094-14-1, 4 February 1972, is changed as follows: 1. The title is changed to read as shown above. 2. Remove old pages and insert new pages as indicated below. New or changed material is indicated by a vertical bar in the margin of the page. Remove pages i and ii Insert pages i and ii 7-1 through 7-11
3. File this change sheet in front of the publication for reference purposes.
By Order of the Secretary of the Army:
Official:
FRED C. WEYAND General, United States Army Chief of Staff
VERNE L. BOWERS Major General, United States Army The Adjutant General Distribution: To be distributed in accordance with DA Form 12-34, Section II, (qty rqr block No. 75) requirements for Calibration Procedures Publications.
TM 9-6625-1094-14-1 C1 Change No. 1 HEADQUARTERS DEPARTMENT OF THE ARMY WASHINGTON, D.C. 8 March 1974
Operator's, Organizational, Direct Support and GENERAL SUPPORT MAINTENANCE MANUAL: TIME BASE PLUG-IN TEKTRONIX TYPE 3B4 TM 9-6625-1094-14-1, 4 February 1972, is changed as follows: * Page 5-2. "Figure 5-1" is added for figure number. Page 5-7. The following is added between C151 and C159 for Serial Numbers 5300 and above: Tektronix Part No. 281-0524-00 150 pf
Ckt. No. C156
Description Cer 500 v
Page 5-11. The following is added between R155 and R157 for Serial Numbers 5300 and above: Tektronix Part No. 315-0820-00 82 ohms
Ckt. No. R156
Description 1/4 w 5%
* First foldout, BLOCK DIAGRAM, CMD 864. "Figure 5-2" and page "5-15" are added. * Page 5-17. "Figure 5-3" is added. * Third foldout, SWEEP GENERATOR, CMD 166. "Figure 5-4" and page "5-19" are added. Page 5-19, figure 5-4, SWEEP GENERATOR circuit. For Serial Numbers 5300 and above, components, as shown by miniature hands in the following diagram, are added.
* Indicates pen-and-Ink changes have been made in the manual.
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TM 9-6625-1094-14-1
* Fourth foldout, TIMING SWITCH, CMD 864. "Figure 5-5" and page "5-21" are added. * Fifth foldout, MAGNIFIER SWITCH, CMD 864. "Figure 5-6" and page "5-23" are added. * Sixth foldout, HORIZONTAL AMPLIFIER, CMD 864. "Figure 5-7" and page "5-25" are added.
2
TM 9-6625-1094-14-1 By Order of the Secretary of the Army:
Official:
CREIGHTON W. ABRAMS General, United States Army Chief of Staff
VERNE L. BOWERS Major General, United States Army The Adjutant General
Distribution: To be distributed in accordance with DA Form 12-34 (qty rqr block No. 75) requirements for Calibration Procedures Publications.
TM 9-6625-1094-14-1 TECHNICAL MANUAL No. 9-6625-1094-14-1 HEADQUARTERS DEPARTMENT OF THE ARMY WASHINGTON, D. C., 4 February 1972 Operator's, Organizational, Direct Support, and GENERAL SUPPORT MAINTENANCE MANUAL, INCLUDING REPAIR PARTS AND SPECIAL TOOLS LIST: TIME BASE PLUG-IN, TEKTRONIX TYPE 3B4 (NSN 4931-00-910-8226) Page Section 0 1 2 3 4 5 6 7 APPENDIX INTRODUCTION ............................................................................................................. CHARACTERISTICS ....................................................................................................... OPERATING INSTRUCTIONS ......................................................................................... CIRCUIT DESCRIPTION.................................................................................................. MAINTENANCE AND CALIBRATION ............................................................................... PARTS LIST AND DIAGRAMS ......................................................................................... PREVENTIVE MAINTENANCE INSTRUCTIONS............................................................... REPAIRS PARTS LIST.................................................................................................... REFERENCES ................................................................................................................ BASIC ISSUE ITEMS LIST............................................................................................... MAINTENANCE ALLOCATION CHART............................................................................ 0-1 1-1 2-1 3-1 4-1 5-1 6-1 7-1 A-1 B-1 C-1
A. B. C.
Change 2, i
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ii, Change 2
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SECTION 0 INTRODUCTION SCOPE This manual includes installation and operation instructions and covers organizational, direct support (DS), and general support (GS) maintenance. It describes Time Base Plug-In, Tektronix Type 3B4. The basic issue items list appears in Appendix B. Appendix B is current as of 24 November 1971. INDEXES OF PUBLICATIONS DA Pam 310-4. Refer to the latest issue of DA Pam 310-4 to determine if there are any new editions, changes, or additional publications pertaining to the equipment. DA Pam 310-7. Refer to DA Pam 310-7 to determine whether there are Modification Work Orders (MWO's) pertaining to the equipment. FORMS AND RECORDS Reports of Maintenance and Unsatisfactory Equipment. Use equipment forms and records in accordance with instructions given in TM 38-750. Report of Packaging and Handling Deficiencies. Fill out and forward DD Form 6 as prescribed in AR 700-58 (Army), NAVSUP Pub 378 (Navy), AFR 71-4 (Air Force), and MCO P4030.29 (Marine Corps). Discrepancy in Shipment Report. Fill out and forward Discrepancy in Shipment Report (DISREP) (SF 361) as prescribed in AR 55-38 (Army), NAVSUP Pub 459 (Navy), AFM 75-34 (Air Force), and MCO P4610.19 (Marine Corps). Reporting of Errors. The reporting of errors, omissions, and recommendations for improving this manual is encouraged. Reports should be submitted on DA Form 2028, Recommended Changes to Publications, and forward direct to: Commander, U.S. Army TMDE Support Group, ATTN: AMXTM-LML, Redstone Arsenal, AL 35898-5400.
Change 3 0-1
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SECTION 1 CHARACTERISTICS Introduction The Type 3B4 Time Base plug-in unit is designed to be used primarily with the Tektronix Type 561A Oscilloscope system; however, it can also be used with the other 560-Series 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 signals. 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 µsec/div to 5 sec/div in 25 calibrated steps. A five-step, directreading 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 µsec/div to approximately 12.5 sec/div and deflection sensitivities from 0.2 volts/div to approximately 12.5 volts/div are available. Uncalibrated operation is indicated by a neon lamp. Normally, the Type 3B4 is inserted in the right-hand compartment (operator's right, oscilloscope's left) of the oscilloscope 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 signals in a Type 561A. Triggering Facilities TRIGGER MODE Switch TRIGGERING LEVEL Control SLOPE Switch COUPLING Switch SOURCE Switch Free Run, Auto, Normal, and Single Sweep See Tables 1-1 and 1-2. + or Ac, Ac Low-Frequency Reject, and Dc Internal, Line, External, and External ÷ 10
TRIGGERING LEVEL Control Voltage Range (external triggering) See Table 1-1. TABLE 1-1 Voltage Range SOURCE EXT EXT ÷ 10 COUPLING AC, DC or AC LF REJ AC or DC AC LF REJ NOTE The voltage range of the TRIGGERING LEVEL control 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 TRIGGERING LEVEL control voltage range. Triggering Sensitivity. See Table 1-2. Typical +19v +190v Minimum +15v +150v
TABLE 1-2 Voltage Range AC LF REJ 1 minor division of deflection 30 kc to 20 mc. Outside these limits requires larger triggering signal. 0.2 v 30 kc to 20 mc. Outside these limits requires larger triggering signal.
SOURCE
INT
AC 1 minor division of deflection 30 cps to 20 mc. Outside these limits requires larger triggering signal. 0.2 v 30 cps to 20 mc. Outside these limits requires larger triggering signal.
EXT
DC 1 minor division of deflection dc to 20 mc (with trace vertically centered). Above 20 mc requires larger triggering signal. 0.2 v dc to 20 mc (with trace vertically centered). Above 20 mc requires larger triggering signal.
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TM 9-6625-1094-14-1
Characteristics-Type 3B4 Automatic Triggering. In this mode of operation a brightline sweep is displayed automatically in the absence of a trigger. The sweep triggering characteristics stated previously also apply for automatic triggering except that the triggering signal must be higher than about 20 cps. The TRIGGERING LEVEL control operates when a triggering signal is present. Single Sweep. This feature permits only one triggered sweep following each reset pulse. The reset pulse is generated by pressing the PUSH TO RESET button. The triggering characteristics stated previously apply. EXT TRIG IN Connector Input Characteristics. Table 1-3. TABLE 1-3 See
+ GATE OUT Connector Sweep Length
Provides a +20-volt (±10%) output pulse during sweep time. 10.5 ±0.3 major division.
Sweep Amplifier (when used as an external horizontal amplifier) Facilities HORIZONTAL VOLTS/DIV Switch VARIABLE Control EXT HORIZ IN Connector Frequency Response Maximum Input Voltage Environmental Operating TEMPERATURE ALTITUDE VIBRATION 0°C to +50°C. 10,000 feet maximum. 0.015 inch peak-to-peak, (1.9 G,s) for 15 minutes along each axis. Vibration frequency varied from 10-50-10 cps in 1-minute cycles.
Calibrated volts/div steps of 0.2, 0.5, 1, 2, and 5 volts/div. Accuracy ±3% when calibrated to match the oscilloscope in which used. The amplifier is dc coupled to the EXT HORIZ IN connector. Multiplies volts/div of any step by a factor variable from 1 to 2.5. Input R and C is typically 1 meg shunted by 40 pf. Dc to 400 kc. Response 30% down at 400 kc with the VARIABLE control set to CALIB position. ±20 volts dc, or 20 volts peak ac.
Non Operating TEMPERATURE ALTITUDE VIBRATION TRANSIT 0.2 µsec/div to 5 sec/div in 23 steps, 1, 2, 5 sequence. The calibration accuracy (unmagnified) is ±3% from 0.2 µsec/div to 2 sec/div; ±5% at 5 sec/div. Uncalibrated variable time/div control. Multiplies the sweep time/div of any step of the TIME/DIV switch by a factor variable from 1 to 2.5. Coarse horizontal positioning to position any portion of the trace to the center of the crt. The FINE control has a range of about 2 minor divisions. Provides direct readout magnification of the sweep (up to 50X). The magnifier also provides the 0.05 and 0.1 µsec/div sweep rates. Magnified sweep accuracy, ±5% (exception: 5 sec/div). Magnified sweep registration, ±1 minor division. -35°C to +60°C. 50,000 feet maximum. 0.015 ±0.003 inch total displacement from 10 to 5 cycles. 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.
Sweep Facilities TIME/DIV Switch
VARIABLE Control
Mechanical Construction Dimension (approx.) Net Weight Accessories Information on accessories for use with this instrument is included at the rear of the mechanical parts list. Aluminum-alloy chassis with chromeplated side rails. Front panel is photoetched and anodized. 6 1/4 inches high, 4 1/4 inches wide, 14 1/2 inches deep (overall). 4.5 pounds.
POSITION Controls MAGNIFIER Control
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TM 9-6625-1094-14-1
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 Operation" later in this section. TRIGGER MODE Switch FREE RUN AUTO Selects the manner in which the Time Base sweeps are initiated. For example: In this position, recurrent sweeps are provided. 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 position. Normal method of operation. Each sweep is triggered by the signal from the internal 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 triggered 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 triggering signals can be attenuated by using the EXT ÷ 10 position. Permits acceptance or rejection of some triggering signal characteristics: Rejects dc and attenuates very lowfrequency ac triggering signals. Ac low-frequency reject. Rejects dc and discriminates against low-frequency ac triggering signals. The 30% down point is 17 kc. Accept ac and dc triggering signals. Determines whether triggering will occur during the positive-going (+) or negativegoing (-) portion of the triggering signal. Selects the amplitude point on the triggering signal where triggering will occur.
TIME/DIV OR HORIZONTAL VOLTS/DIV
NORM SINGLE SWEEP and PUSH TO RESET SOURCE INT LINE
MAGNIFIER
EXT and EXT ÷ 10 COUPLING AC AC LF REJ
VARIABLE
DC SLOPE (+ or -) TRIGGERING LEVEL
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 control is in the CALIB position. The number bracketed by the two heavy black lines on the clear plastic knob flange is the unmagnified sweep time per division. To change the unmagnified sweep rate, the concentric flange and the MAGNIFIER knob must first be interlocked by positioning 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 deflection. Provides magnification of the time base display up to 40X or 50X in five directreading steps (Magnification of the four fastest unmagnified sweep rates is limited to 0.05 µsec/div). For example, at 10X magnification, the 5 minor division segment at the center of an unmagnified crt display is horizontally expanded to full graticule width. Any other 5 minor division 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 conditions necessary for most measurements. In many applications, it is desirable for a repetitive signal to produce a stationary
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TM 9-6625-1094-14-1 Operating Instructions-Type 3B4
Fig 2-1. Front Panel Controls and Connectors.
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TM 9-6625-1094-14-1
Operating Instructions-Type 3B4 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 triggering 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 operation and because of the reference trace produced in the absence of a triggering signal. The time base free runs without 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 control 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 photographing non-repetitive 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 yield 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 confusion 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 inoperative and the lamp extinguishes. A 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 control range. DC. Dc coupling allows the trigger circuits to receive signals of all frequencies from dc upward. It is best to dc couple for very low-frequency signals (below about 20 cps). AC. Ac coupling rejects the dc 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 attenuates ac signals as frequency decreases (30% down point 17 kc). 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 instantaneous voltage on the triggering signal at which the sweep is triggered. (This instantaneous voltage can also include a dc level if the COUPLING switch is set to DC.)
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Operating Instructions-Type 3B4 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. Likewise, with the SLOPE switch at -, adjusting the TRIGGERING 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 MAGNIFIER The Time Base has 23 calibrated sweep rates ranging from 0.2 µsec/div to 5 sec/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 control 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 VARIABLE 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. Uncalibrated sweep rates are indicated when the UNCAL lamp is lit. The sweep ranges between 5 sec/div and 2 µsec/div can be magnified up to 40X or 50X in 5 steps. The degree of magnification is the ratio between the indicated magnified rate (number opposite the dot on the skirt of the MAGNIFIED 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 µsec/div the number of steps of magnification decrease until at the .2 µSEC setting of the TIME/DIV switch only two steps of magnification are available. The .2 µSEC position is the highest sweep rate to which the TIME/DIV switch can be set, but by the use of the two additional magnified positions, and effective sweep rate of 50 nSEC/DIV is obtained. FIRST-TIME OPERATION The following control and switch settings for the Type 3B4 can be used for a wide range of measurements. The operating conditions established by these settings also provide a starting point for the operator who is learning to use the instrument. TRIGGER MODE COUPLING SOURCE VARIABLE (TIME/DIV) MAGNIFIER AUTO AC INT CALIB fully clockwise) Locked to TIME/DIV switch To position the TIME/DIV switch to the EXT HORIZ IN position, turn the MAGNIFIER knob until the dot on the knob is positioned between the two block 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.
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 amplifier 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 sensitivity are available. The five sensitivity ranges are from 0.2 volts/div to 5 volts/div.
The Type 3B4 now provides the time base for measurements of vertical deflection signals above about 20 cps. In many cases, only the TIME/DIV switch and the TRIGGERING 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 50 kc the vertical deflection amplitude must be at least 1 minor division. See Table 1-2.
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Operating Instructions-Type 3B4 3. The TRIGGERING LEVEL control must be properly adjusted. If 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 function 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 squarewave output. Set the Type 3B4 controls as outlined in Table 2-1. TABLE 2-1 Typical Control Settings for Time Measurements Control TRIGGER MODE TIME/DIV MAGNIFIER SLOPE COUPLING SOURCE VARIABLE Settings AUTO 1 mSEC 1 mSEC (--) AC INT CALIB Example 2, Risetime Check: At the completion of the measurement listed in Example 1, unlock the MAGNIFIER knob by pulling it out, then, while holding it out, set it to the 20 µSEC 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 control of the vertical plug-in amplifier to move the 90% point down to the horizontallyscribed centerline. The 90% point will intersect the horizontally-scribed centerline less than one major graticule division to the right of the vertically-scribed centerline, thus providing a 10% to 90% risetime of less than 20 µsec. Example 3, Type 3B4 Used as a Trigger Source: Ordinarily, the signal to be displayed is also used to trigger the oscilloscope. In some instances, it may be desirable to reverse this situation. The sweep-related output pluses, available 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 display while the oscilloscope free runs. For this type of operation, set the controls on the Type 3B4 as listed in Table 2-1 except set the TRIGGER MODE switch to FREE RUN. Connect the Type 3B4 +GATE OUT output to the external device 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 oscilloscope system to be used to plot one function against another (e.g., Lissajous figures). However, the system is not intended for precise phase-angle measurements. To use an external signal for horizontal deflection, connect 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 by changing the MAGNIFIER switch when using horizontal deflection. To change sensitivity, MAGNIFIER knob out to unlock it, then set to the position of the SEC OR EXT VOLTS positions. changed external pull the selected
With the controls set as outlined in Table 2-1, apply a 2volt 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 vertical plug-in POSITION control until the vertical deflection extends 2 divisions above and 2 divisions below the horizontally scribed centerline. Turn the POSITION and FINE control 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 half-cycle 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.
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SECTION 3 CIRCUIT DESCRIPTION Introduction This section contains the theory of operation of the various circuits in the Type 3B4. The discussions ore supported by the block diagram and schematics in Section 5. The relationship of the circuits in a particular block to those in other portions 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 linearramp horizontal deflection voltage, and in addition, adapts externally generated signals to provide horizontal deflection when such operation is desired. From the Sweep Generator 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 frequency but with greater wave-shape consistency than the signals generally encountered. The Trigger Generator converts the triggering signal into a pulse having a consistently fast risetime while retaining the characteristic repetition frequency 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 lowvoltage 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 dc. From the COUPLING switch, the signal is applied through SLOPE switch SW10 to one side of a longtoiled 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 SW10 in the + position, TRIGGERING LEVEL control R16A applies conducting bias to V24B. With V24B conducting, the current flow through R22 develops a voltage which keeps V24A cut off. When the triggering signal 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 triggering 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 is strapped to the +125 volt supply through diode D28. When the comparator is switched by the triggering signal and V24A starts to conduct, the conduction 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 conduction of Q24 provides about 2.5 ma of current to D30 which causes D30 to switch to its high voltage 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 increase 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 Q34 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 HORIZONTAL VOLTS/DIV switch is set to any of the TIME/DIV positions, the Sweep Generator (see Block Diagram)
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Circuit Description-Type 3B4 produces four simultaneous output signals: 1. A positive-going sawtooth that is applied to the Horizontal 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 sync 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 amplitude, 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 Goring circuit can be switched by a pulse from the Trigger Generator. 3. FREE RUN results in recurrent sweeps that are independent 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 Gating 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 pulse; exceeds 80 msec, the Auto Trigger Multi reverts to thc 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 Conditions. In the quiescent state, that is, when the sweep generator is triggerable and is waiting 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 3.8 ma, 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 operating point of cathode follower V173A. 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 collector voltage cuts off V173B 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 trigger 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 voltage on its collector goes negative and reverse biases Disconnect 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 Disconnect 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 V161A goes negative. The tube amplifies 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 V161A. (The positive going voltage also reverse biases D161 and cuts off Q164). This action persists throughout the sawtooth period A
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Circuit Description-Type 3B4 and limits the total damage of grid voltage of V161A to less than 0.5 volt. Since the voltage drop across the timing resistor is held nearly constant, 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 con be varied by turning the VARIABLE front panel control (R160W) shown on the Timing Switch schematic. This control permits the operator to obtain uncalibrated sweep rates at least two and one half times slower than the calibrated rates obtained with the control 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 voltage 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 Q144 and Q184. The time duration of the trigger pulses from the Trigger Generator, which switch D143 to its high voltage state and start the cycle of operation, will always be considerably less than the time duration of the sweep. However, once a sweepgating 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 conduction 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 associated 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 Runup 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. When the sweep ends and the voltage on the cathode of V173A returns to its quiescent level, the voltage at the wiper A 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 conduction. 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 conduction until the charge on the holdoff capacitor is removed by current through R175 and R177. When the charge decreases 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 required 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 TRIGGERING LEVEL control. FREE RUN Mode. When the TRIGGER MODE switch is set to FREE RUN, sweep gating tunnel diode D143 is connected through L139, R116, and the TRIGGER MODE switch to +125 volts. This current path provides approximately 2.2 ma, which added to the approximately 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 Lockout 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 TRIGGER 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 control) 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 permits 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
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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 approximately 80 milliseconds or less. If a second trigger pulse is received 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 milliseconds. As long as incoming trigger pulses arrive at intervals shorter than about 80 milliseconds, the sweep is triggered 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 initiated sweep is in progress. In this case the Sweep Generator cannot 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 repetition 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 it connected to +125 volts, which serves to keep D179 reverse biased at all times. As the TRlGGER MODE switch is turned from NORM position to the SINGLE SWEEP position, 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, it is necessary to press the PUSH TO RESET switch (SW135). Pressing the PUSH TO RESET switch applies -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 whenever 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 arrangement of the horizontal amplifier circuits. The input to the Horizontal Amplifier proper is taken from the output of cathode follower V173A in the Miller Runup circuit. Normally, the signal input to the Horizontal Amplifier is the sweep ramp voltage. However, when the TIME/DIV OR HORIZONTAL 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 follower 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 controls. The EXT HORIZ GAIN control is a screwdriver adjustable 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 control R402 provides a means of adjusting the amount of signal drive to the Horizontal Amplifier. Front panel FINE and POSITION controls apply dc voltages to the base of Q414, which in turn establishes the operating points of the transistors in the output stages of the Horizontal Amplifier. (Changing the dc 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 horizontal input signals are used. The output of Q414 is applied to the input of a paraphase amplifier consisting of Q424, Q434, Q423, Q433, and associated 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 920 when no magnification is used (X1) and is decreased to about 20 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 applied through pins 17 and 21 of the interconnecting plug to the horizontal deflection plates of the crt. A
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SECTION 4 MAINTENANCE AND CALIBRATION1 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 components). Hardened dirt may be removed with a dry, soft point 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 lack and plug should be lightly lubricated with on oil of the type used on switch contacts. To extend the life of the contacts, clean and relubricate if the oil 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, overheating 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 maintenance checks on the tubes and transistors used in the instrument are not recommended. The circuits within the instrument generally provide the most satisfactory means of checking tube or transistor performance. Performance of the circuits is thoroughly checked during recalibration so that substandard tubes and transistors will usually be detected at this time. Recalibration. To insure accurate measurements, the instrument calibration should be checked after each 500 hours of operation or every six months if used intermittently. Complete calibration instructions are contained later in this section. 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 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 remember that the physical size and shape of a component may affect its performance at high frequencies. After repair, portions of the instrument may require recalibration. Soldering. Special silver-bearing solder is used to establish a bond to the ceramic terminal strips in Tektronix instrument. 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. 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 concentrated 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 containing about 3% silver. 3. Use long-nose pliers for a heat sink. Attach pliers between 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. Overfilling 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. 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 ore manufactured for Tektronix to our specifications. See "Parts Ordering Information" and "Special Notes and Symbols" on the first page of Section 6 and page 4-10.
General Information. Certain parts in the instrument are Ceramic Strip Replacement. Unsolder all connections, most easily replaced if definite procedures are followed as then use a 3/8" diameter by 3" long plastic or hardwood outlined in the following paragraphs. __________ 1 This procedure is to be used only for maintenance. For calibration procedure, see TB 750-236.
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Maintenance and Calibration-Type 3B4 dowel and a small (2 to 4 oz.) 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 terminal strip is to use diagonal cutters to cut off the side of the stud that holds the ceramic strip. The ceramic strip is removed 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 thoroughly in the spacers. Be sure that these pins are driven completely through the spacers. You may wish to 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. 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 resistances 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