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              SPECTRUM DISPLAY
                                  3720A




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         *-
                                                         -
                                                         -
                                                         -
                                       HEWLETT
                                                        u'TPACKARD


                                           SERVICE MANUAL




                                            MODEL 3720A
I-
                                       SPECTRUM DISPLAY

J.



                                                 SERIAL PREFIX

                            This manual applies to all instruments having serial prefix
                            1209U. Instruments with a serial prefix above 1209U may
                            have a Manual Change Sheet, to which reference should be
                                                     made.




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                                                                                                 ,.


                                  Copyright HEW LETT-PACKAR D LIMITED 1972
                               SOUTH QUEENSFERRY, WEST LOTHIAN, SCOTLAND




     03720-95001                                                                          Printed: APRIL 1972



                                                                                                                I
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Foreword




                                                FOREWORD


           For convenience and ease of use, information on Model 3720A Spectrum Display
           has been presented in two publications:


              .OPERATING MANUAL                 hp Part Number 03720-95000
                                                (Microfiche 03720-95025)

               .SERVICE MANUAL                  hp Part Number 03720-95001
                                                (Microfiche 03720-95026)



                                               HOW TO ORDER

           To order the above publications contact the nearest Hewlett-Packard Sales and
           Service Office (addresses a t the rear of this manual). Give the hp Part Number of
           the publication and the complete model number, name and serial number of the in-
           strument.



                                           SERVICE MANUAL CONTENT

           Section I         contains General Servicing Instructions and a Description of Controls
                             and Indicators.

           Section I         gives information on Parts Identification, Maintenance and Repair
                             Procedures.

           Section II contains a list of Replaceable Parts for the 3720A.

           Section V         gives the 3721A/3720A System Troubleshooting Procedure.

           Section V         contains the Functional Diagram, Assembly Location Diagrams and
                             Assembly Packages including Schematic and Component Location.



                                                  MICROFICHE

           rhese publications are also available in 6in x 4in microfiche form. Each sheet contains
           up to 60 pages, maximum, of text and illustrations. Order as above, quoting the
           appropriatehpmicrofiche part number.



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                                                                                                               List of Contents



                                                   LIST OF CONTENTS

                                              SECTION I INTRODUCTION


Paragraph     1.1          OPERATING INSTRUCTIONS . . . . . . . . . . . .                                         .. Page     1-1
              1-3          GENERAL SERVICING INSTRUCTIONS . . . .                                                    ....     1-1

Table         1-1         Accessories furnished with 3720A . . . . . . .                                                      1-1

Figure        1-1          Model 3720A Spectrum Display . . . . . . . . . . . . . .                                          1-0
              1-2          Front panel controls and indicators . . . . . . . . . .                                           1-2
              1-3          Rear panel controls and connectors ..          ...                                                1-4


                                        SECTION II GENERAL MAINTENANCE


Paragraph    2-1          INTRODUCTION . . . . . . . . .                                                          .. Page 2-1
             2-3          IDENTIFICATION . . . . . . . . .                                                        . . . . . . 2-1
                          2-4   Assembly Identification . . . . . . . . .                                               . . . 2-1
                          2-6  Assembly Connection Identification ..                                                    . . . 2-1
                          2-8   Integrated Circuit Identification . . .                               ...                     2- 1
             2-15         INSTRUMENT DlSMANTLl NG . . . . . . . . . . . .                           ........           . . . 2-2
                          2-16 Removing Top and Bottom Covers . . . .                               ........            . . . 2-2
                          2-17 Removing Side Covers . . . . . . . . . . .                             ...                     2-2
                          2-18 Front Panel Access . . . . . . . . . . . . .                                                   2-3.
             2-19         MAINTENANCE
                          2-20 Locations of dc Power Supply Fuses . . . . . . .                                      ...     2-3
                          2-23 Replacement of Display Sensitivity Lamps . . .                                        ...     2-3
                          2-27 Cleaning the Air Filter . . . . . . . . . . . . . .                                   ...     2-4
                          2-29 Cathode Ray Tube RemovaI/RepIacement . . . . . . . . . . . . . .                      ...     2-4
                          2-30 Line Transformer Removal/Replacement . . . . . . . . . . . . . . . .                  ...     2-5
                          2-31 Chassis Mounted Transistors Plate Removal/Replacement . . . .                         ...     2-5
                          2-32 High Voltage Tripler Assembly Removal/Replacement . . . .                             ...     2-5
             2-33         REPAIR PROCEDURES . . . . . . . . . . . . . . . . . . . . . . . . . . . .                  ...     2-5
                          2-34 Etched Circuits . . . . . . . . . . . . . . . . . . . . . . .                         ...     2-5
                          2-36 Integrated Circuit Removal/Replacement                                                . . .   2-6

Table        2- 1         3720A Assem bl ies . . . . . . . . . . . . . .                                             ...     2-1
             2-2          Digital integrated circuit abbreviations         ....                                              2-2

F igure      2- 1         A18/A19 Housing assembly retaining screws ..                                               ...     2-3
             2-2          CRT neck connections . . . . . . . . . . . . . . . .                                       ...     2-4


                                         SECTION 111 REPLACEABLE PARTS


Paragraph   3- 1         I NT R 0 DUCT I0 N . . . . . . . . . .                                                . . . . Page 3-1
            3-3          ORDERING INFORMATION ..                                                                  .....      3-1
            3-7          REFERENCE DESIGNATORS ..                                                                      ..    3-1
                                                                                                                              ...
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        Model 3720A



                    3-8       LIST OF ABBREVIATIONS ..
                    3-9       COLOUR ABBREVIATIONS ..

        iable       3- 1      Replaceable Parts . . . . . . . . . .                                        ........           .. 3-4
                    3-2       Code List of Manufacturers . . . . .                                         ........           .. 3-50
                                                                                                                                                   P

        Figure      3- 1       Location of cabinet components ..                                                              .. 3-49




                                          SECTION IV SYSTEM TROUBLESHOOTING


        Paragraph   4-1       INTRODUCTION . . . . . . . . . . . . . . . . . . . .                                    . . . Page 4-1
                    4-3       USING TROUBLESHOOTING SECTION ..                                                              . . . . 4-1
                    4-8       TEST EQUIPMENT . . . . . . . . . . . . . . . . . . . . . . . . . .                                 .. 4-2
                              4-10 Logic Probe . . . . . . . . . . . . . . . . . . . . . . . . . . . . .                         .. 4-2
                    4-12      SYSTEM TROUBLESHOOTING CONTROLS SET-UP                                                             .. 4-3
                    4-14      FLOW A . Control Faults . . . . . . . . . . . . . . . . . . . . . .                                .. 4-5
                    4-16      FLOW B . Display Sensitivity Faults . . . . . . . . . . . .                                        .. 4-6        c

                    4- 19     FLOW C . Transfer Faults ,. . . . . . . . .
                                       Data                                                                                      .. 4-7
                    4-21      FLOW D . Other Transferred Signals Faults . . . . . . . .                                          .. 4-8
                    4-23      FLOW D(a) . Timescale Transfer Faults . . . . . . . . . . . .                                      .. 4-8        k

                    4-25      FLOW D(b) . Correction Factors Transfer Faults ..
                                          Gain                                                                                   .. 4-9
                    4-27      FLOW D(c) . Signal Recovery Transfer Faults . . . . . .                                            .. 4-10                   I

        rable       4- 1      Flow charts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .                 .. 4-1
                    4-2
                    4-3
                              3721A/3720A System repair procedure . . . . . . . . . . . .
                              Test equipment required for System Troubleshooting ..
                                                                                                                              ..  4-1
                                                                                                                              .. 4-2
                                                                                                                                           9
                    4-4       Range transfer check . . . . . . . . . . . . . . . . . . . . . . . . . .                        .. 4-6
                    4-5       Range data logic check . . . .                          ...                                     .. 4-6
                    4-6       Ti mescale transfer check . . . . . . . . . . . . . .                                           .. 4-9
                    4-7       Gain correction factors check . . . . . . . . . .                                               .. 4-10
                    4-8       Signal recovery transfer check ..                       ...                                     .. 4-10
        Figure      4- 1      750KHz . . . . . . . . . . . . . . . . . .                                                      .. 4-4
                    4-2       Transfer Data duration . . . . . .                                                              .. 4-4
                    4-3       Data Ready . . . . . . . . . . . . . .                                                          .. 4-4
                    4-'4      Transfer Data repetition rate ..                                                                .. 4-4
                    4-5       Multiplexed range outputs ..                                                                       4-6
                                                                                                                                               c

                                                                                                                                           Y

                            SECTION V SCHEMATICS. COMPONENT LOCATIONS. DIAGRAMS


        Paragraph   5-1       INTRODUCTION . . . . .                                                                  . . . . Page 5-1
                    5-3       DRAWING SYMBOLS . . . . . . . . . . .                                                      .....   5-1
                    5-5       ASSEMBLY PACKAGES . . . . . . . . . . . .                                                  .....   5-1
                              5-7  Locating Assembly Packages . . . .                                                         .. 5-1
                    5-9       THEORY OF OPERATION . . . . . . .                                                               .. 5-1
                              5-10 Functional Diagram ..                                                                      .. 5-1

        Figure      5-1
                    5-2
                              Guide to schematics ..
                              Logic package outlines
                                                                                                                              ..   5-2
                                                                                                                              .. 5-3       1'
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            5-3         Functional diagram .. .. .. .. .. .. .. .. .. .. ..                                  .. 5-4
            5-4         Guide to logic symbols .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..            .. 5-4
            5-5         Location of components (front and rear panels) .. .. .. .. .. .. .. ..               .. 5-5
            5-6         Location of assemblies and chassis mounted components (top view) .. .. .             .. 5-6
            5-7         Location of assemblies and chassis mounted components (underside view)            .. .. 5-7
            5-8         Wiring of rotary switches .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .    .. 5-61
            5-9         Wiring of rear panel connectors                                                         5-63



A1   Not Assigned


A2 Mantissa Range Assembly Package
Figure    A2-1 Component location, A2 .. .. .. .. .. .. .. .. .. .. .                                 .. .. Page 5-10
          A2-2 Schematic A2 (part 1 ), Mantissa Range assembly .                                          . .. .. 5-11
          A2-3 Schematic A2 (part 21, Mantissa Range assembly                                                     5-13


A3 Decade Range Assembly Package
Figure   A3-1 Component location, A3 .. .. .. .. .. .. .                  .. .. .. ..   .. .. .. ..      . Page 5-14
         A3-2 Schematic A3, Decade Range assembly .                       .. .. .. ..   .. .. .. ..      . .. .. 5-15


A4 Store 1 Assembly Package
Table      A4-1 Component identification grid, A4                                                        . Page 5 1 7

Figure      A4-1         Component location, A4      .. .. .. .. .. .,                                        .. 5-16
            A4-2         Schematic A4 (part 11, Store 1 assembly ..                                           _. 5-17
            A4-3         Schematic A4 (part 21, Store 1 assembly ..                                           .. 5-19


A5 Store 2 Assembly Package
Figure     A5-1 Component location, A5 .. .. .. ..                                                    _. .. Page 5-20
           45-2 Schematic A5, Store 2 assembly . _                                                        . .. .. 5-21


A6 Buffer Assembly Package
Figure  . A6-1   Component location, A6 .. .. .. ..                                                      . Page 5-22
          A6-2 Schematic A6, Buffer assembly ._                                                          . _ _ _ _ 5-23


A7 Switch Card Assembly Package
Table     A7-1 Component identification grid, A7                                                         . Page 5-25

Figure      A7-1         Component location, A7 .. .. .. .. ._ .                                              .. 5 2 4
            A7-2         Schematic A7, Switch Card assembly .. ..                                             .. 5-25


A8 Hybrid Multiplier Assembly Package
Table     A8-1 Component identification grid, A8 .. .                                                 .. .. Page 5-27

Figure      A8-1         Component location, A8 .. .. .. .. ._ .. .. ._                                       _. 5-26
            A8-2         Schematic A8, Hybrid Multiplier assembly ..                                          .. 5 2 7    ,




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Model 3720A



A9 Window Multiplier Assembly Package
Table     A9-1 Component identification grid, A9 ..                                                            .. Page 5-29

F igure     A9-1      Component location, A9 . . . . . . . . . . . . . . .                                       . . . . 5-28
            A9-2      Schematic A9, Window Multiplier assembly ..                                                ....    529


A10 Integrator Assembly Package
Table       A10-1 Component identification grid, A10               ..                                          .. Page 5-31

Figure      A10-1 Component location, A10 . . . . . . . . . .                                       ........     . . . . 5-30
            A10-2 Schematic A10, Integrator assembly ..                                             ........     . . . . 5-31


A1 1 Polar Converter Assembly Package
Table       A1 1-1 Component identification grid, A1 1                                                           Page 5-33

F igure     A1 1-1 Component location, A1 1 . . . . . . . . . . . .                                              .... 532
            A1 1-2 Schematic A1 1, Polar Converter assembly . . . .                                                 . 5-33


A1 2 Low Voltage Power Supply Assembly Package
Table      A12-1 Component identification grid, A12                ..........                                  .. Page 5-37
                                                                                                                                          1



Figure      A12-1     Component location, Chassis Mounted Transistors . . . . . . . .               ........     . . . . 5-34
            A12-2     Schematic, Line Module and Line Transformer . . . . . . . . . .               ........     . . . . 5-35
            A12-3     Component location, A12 . . . . . . . . . . . . . . . . . . . . . . .           ...        _. ._ 5-36
            A1 2-4    Schematic A1 2, Low Voltage Power Supply assembly .                                              . 5-37


A1 3 Control Logic Assembly Package
Table       A13-1 Component identification grid, A13               ..                                          .. Page 5-39

Figure      A13-1 Component location, A13 . . . . . . . . . . . . . . . . . . . .                                .. _. 5-38
            A13-2 Schematic A13 (part 11, Control Logic assembly ..                                              . . . . 5-39
            A13-3 Schematic A13 (part 2), Control Logic assembly ..                                              .... 541


A14 Triangle Wave Generator Assembly Package
Table       A14-1 Component identification grid, A14               ..                                          .. Page 5-43

Figure      A14-1 Component location, A14 . . . . . . . . . . . . . . . . . . . . . . . . . . . .                .... 542                 r

            A14-2 Schematic A14 (part 11, Triangle Wave Generator assembly ..                                    . . . . 5-43
                                                                                                                 . . . . 5-45
            A14-3 Schematic A14 (part 2), Triangle Wave Generator assembly ..
                                                                                                                                          .
A15 Sine Shaper Assembly Package
Table      A15-1 Component identification grid, A15                                                            .. Page 5-47

Figure      A 1 5 1 Component location, A15 . . . . . . . . . . . . . . .                                        . . . . 5-46
            A1 5-2 Schematic A1 5 (part 11, Sine Shaper assembly ..                                              . . . . 5-47
            A15-3 Schematic A15 (part 21, Sine Shaper assembly ..                                                     ,. 5-49




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                                                                                            List of Contents



            A16 Deflection Amplifiers Assembly Package
            Table       A16-1 Component identification grid, A16                               . Page 5-51

            F igure     A16-1 Component location, A16 .. .. .. .. .. .. .. .. _. .. .. ..           .. 5-50
                        A16-2 Schematic A16 (part l), Deflection Amplifiers assembly ..             .. 5-51
                        A16-3 Schematic A16 (part 21, Deflection Amplifiers assembly              - .. 5-53
1




            A1 7 High Voltage Power Supply Assembly Package
I
            Table       A17-1 Component identification grid, A17                            .. .. Page 5-55

            Figure      A17-1 Component location, A17 .. .. .. .. .. .. .. .. .. .. ..         . .. .. 5 5 4
                        A17-2 Schematic A17, High Voltage Power Supply assembly ..                  .. 5-55



            A1 8 Range Indicator Assembly
            Table       A18-1 LED Truth Table      _.                                        .. .. Page 5-57

            Figure      A18-1 Component location, A18 .. _. .. .. .. .. _.                        ,   .. 5-56
                        A18-2 Schematic A18, Range Indicator assembly ..                              .. 5-57



    i       A19 Range Units Assembly Package
            Figure    A19-1 Component location, A19 .. .. .. .. .. .                        .. .. Page 5 5 6
                      A19-2 Schematic A19, Range Units assembly .                              ,. .. .. 5-57


            A20 Storage Assembly Package
            Table      A20-1 Component identification grid, A20              .. .. .. ..     ._ .. Page 5-59

            Figure      A20-1 Component location, A20 .. .. .;                  .. .           .. .. .. 5-58
                        A20-2 Schematic A20,Storage assembly ..                                   ,   .. 5-59




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Model 3720A




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                                  Figure 1-1 Model 3720A Spectrum Display

1-0


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                                                                                                            Section I



                                                           SECTION I
                                                     INTRODUCTION
        1-1 OPERATING INSTRUCTIONS                                  1-5 Remember, when servicing the 3721A/3720A
                                                                    System, that a high intensity CRT display on the
                                                                    3720A over an extended period of time may cause
        1-2 Detailed operating instructions are contained
                                                                    burn damage to the storage mesh or phosphors of
        in the 3720A Operating Manual but, for conven-
                                                                    theCRT,
        ience, descriptions of the controls, indicators and
        connectors on the front and rear panels of the
        3720A are included in this section.                         1-6 The storage CRT in the 3720A is mechani-
                                                                    cally delicate and is easily damaged by violent
                                                                    movement or by being inverted. To prevent
        1-3 GENERAL SERVICING INSTRUCTIONS
                                                                    accidental damage in use, remember the following
                                                                    points when handling the 3720A:
        1-4 When servicing the 3721A/3720A System,

1




                                            Table 1-1 Accessories furnished with 3720A



    3                           Accessory                                          hp Part Number

                  Detachable Power Cord                                               Various
                  Rack Mounting K i t                                                5060-8742
                  Servicing Extender Board                                          03720-70021
                  3721A/3720A Interface Accessory                                     15549A
                  Trimming Tool                                                      8730-0013
                  Operating Manual                                                  03720-95000
                  Service Manual                                                    03720-95001




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Model 3720A




                                               2                              1         27      26    25    28     29     30


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           3
                                                                                                                                            31
           4
           5                                                                                                                                24
           6                                                                                                                                23
           7                                                                                                                                22
           8

           9

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                                      1'1     1'2   13   14   1'5   16   ii              is                         21




      1.       DISPLAY: 8 y 1 0 division CRT, w i t h graticule                   6.    STORAGE TIME: potentiometer. Varies t h e time
               calibrated in one division squares. Major axes cali-                     any display is stored, when in STORE mode.
               brated in 0.2 division intervals. 1 division = 0.95cm.



                                                                                  7.    FOCUS: potentiometer. Adjusts sharpness o f C R T
      2.       DISPLAY SENSITIVITY: illuminated digital readout.                        beam.
               Scales the horizontal and vertical axes and the fre-
               quency ..interval, Af, as selected b y Scale Factor
               switch.

                                                                                  8.    PERSISTENCE: potentiometer. Controls duration of
                                                                                        written trace, when n o t in STORE mode. F u l l y
                SCALE FACTOR: lever switch. Selects axis calibra-                       clockwise position selects STORE mode.
      3.
                t i o n t o be presented o n the Display Sensitivity panel.


                                                                                  9.    INPUT: lever switch. Routes data f r o m the 3721A
                                                                                        i n t o Store 1 o r 2 as selected. In HOLD position retains
      4.       ERASE: pushbutton. Eradicates all traces displayed
                                                                                        data in stores.
               o n storage C R T screen, when n o t in STORE mode.




      5.        INTENSITY: potentiometer. Controls brightness o f                 10.   LINE-ON: toggle switch. Controls ac supply t o t h e
                CRT beam.                                                               instrument.




                                               Figure 1-2 Front panel controls and indicators

1-2


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                                                                                                                                       Section I




        11.   DATA: lever switch. I n positions 1 o r 2 displays             21.   HORIZONTAL: rotary switch. Selects function t o be
              contents o f respective store on CRT. I n extreme right-             presented on horizontal axis o f CRT. Used together,
              hand position transfers control t o SPECTRUM switch.                 controls 20 and 21 enable the user t o select the
                                                                                   presentation format of the display.

        12.   WINDOW: lever switch. ON position - applies a
              triangular window t o i n p u t data. OFF position        -    22.   CALIBRATION lever switch. Allows external X - Y
              natural window occurs.                                               Recorder p l o t size t o be set.


        13.   SPECTRUM: lever switch. Controls choice o f store              23.   START: pushbutton. Initiates a single sweep of the
              contents t o be transformed.                                         pen across the X-Y Recorder chart.



        14.   REAL/COMPLEX: lever switch.                                    24.   RECORD: Lever switch. Controls outputting o f trace
              R E A L - calculates cosine components only.                         on t o X - Y Recorder.
              COMPLEX - calculates cosine and sine components.

                                                                             25.   HORIZONTAL SHIFT: potentiometer. Moves trace
        15.   GAIN: rotary switch.       Selects    gain o f   integrator.         horizontally o n CRT.


        16.   GAIN VERNIER: potentiometer. Provides continuous               26.   CAL: potentiometer. Adjusts horizontal size o f display.
              gain adjustment between calibrated steps. I n CAL,
I             gain selected b y G A I N switch.
                                                                             27.   HORIZONTAL GAIN: lever switch. Magnifies horiz-
                                                                                   mtal axis o f displayed trace b y a factor of 2.
        17.   OVERLOAD: lamp. Indicates if integrator becomes
              overloaded at any time during processing.
                                                                             28.   PHASE SHIFT: lever switch. Adds 0. +goo, or
        18.   INTERPOLATION: potentiometer. I n the M A N U A L                    -90' phase shift t o any display axis representing
              mode fractionally alters each o f the 100 frequencies                phase information.
              a t which the transform is computed (up t o A f max).
              I n A U T O 10 equally spaced display points are pro-
              duced i n each frequency interval d f .                        29.   VERTICAL SHIFT: potentiometer. Moves trace ver-
                                                                                   tically o n C R T screen.


        19.   MARKER: potentiometer. Puts a marker o n any
                                                                             30.   CAL: potentiometer. Adjusts vertical size o f display.
              p o i n t o f the displayed function.

                                                                             31.   VERTICAL GAIN: lever switch. Provides magnifi-
        20.   VERTICAL: rotary switch. Selects function t o be                     cation o f vertical axis o f displayed trace b y a factor
              presented o n vertical axis of CRT.                                  of 2.




    3                               Figure 1-2 Front panel controls and indicators (continued)
                                                                                                                                               1-3


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Model 3720A




                                1                                        2        4         5             3         6            7




      1.   POWER MODULE: contains ac line socket,               fuse,        4.       X-RECORDER: BNC connector. O u t p u t t o horizontal
           and voltage selector switch.                                               axis o f X-Y Recorder.


           AC Line. 11 51230V. k 10%. 48 t o 65Hz. 250VA.
                                                                             5.       Y-RECORDER: BNC connector. O u t p u t t o vertical
           Fuse. 1 1 5 V -2.5AT, 2 3 0 V -1.25AT.                                     axis of X-Y Recorder.
           C l i p i n fuse. Cannot be changed w i t h o u t first re-
           moving power cable.

           Selector. Lever switch, 115V or 230V line voltage                 6.       PEN LIFT: BNC connector. Provides control signal f o r
           selector. Cannot be changed w i t h o u t first removing                   pen o f an X-Y Recorder w i t h remote pen control
           power cable.                                                               facility.



                                                                                                                                               c
                                                                                      VALID DATA: BNC connector. Provides p signal t o
                                                                                      indicate that valid data is present at X and Y Re-
      2.   EXTERNAL INTERFACE:           50-contact connector.                        corder output connectors.
           Duplicates 3721A Data Interface rear panel connector.




      3.   3720A13721A CONNECTOR: 50-contact connector.
           Input socket f o r data f r o m 3721A.                            NOTE:     -   denotes alternating current ( a d .




                                         Figure 1-3 Rear panel controls and connectors
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                                                                                                              Section II



                                                        SECTION I I
                                            GENERAL MAINTENANCE
             2-1 INTRODUCTION                                       2-6 Assembly Connection Identification

             2-2 This section contains information on Identi-
             fication, Instrument Dismantling and Repair Pro-       2-7 Throughout this manual connections to printed
             cedures for the 3720A.                                 circuit assemblies are referred to by an abbreviated
                                                                    form. For example, the connection to pin M on A5
                                                                    assembly is written as A5(M).
             2-3 IDENTIFICATION

             2-4 Assembly Identification                            2-8 Integrated Circuit Identification

             2-5 Table 2-1 lists the designator, title and hp       2-9 Digital integrated circuits are referenced by
             Part Number of all assemblies in the 3720A             the physical location of each package (MC pre-
             Spectrum Display. (Assembly is abbreviated to          fix) on the circuit board, and by their function in
             Assy in this Table).                                   the circuit (G, FF, etc, as applicable).

                                                 Table 2-1 3720A Assemblies

                        Assemb Iy                                                                   hp Part
                                                            Title
                        Designator                                                                  Number

                             A?                 Not Assigned                                            -
                             A2                 Mantissa Range Assy                               03720-70002
                             4.3                Decade Range Assy                                 03720-70003
                             A4                 Store 1 Assy                                      03720-70004
                             A5                 Store 2 Assy                                      03720-70005

                             A6                 Buffer Assy                                       03720-70006
                             A7                 Switch Card Assy                                  03720-70007
                             A8                 Hybrid Multiplier Assy                            03720-70008
                             A9                 Window Multiplier Assy                            07320-70009
                             A1 0               Integrator Assy                                   03720-70010

                             A1 1               Polar Converter Assy                              03720-70011
                             A12                Low Voltage Power Supply Assy                     03720-70012
                             A13                Control Logic Assy                                03720-70013
                             A14                Triangle Wave Generator Assy                      03720-70014
                             A1 5               Sine Shaper Assy                                  03720-70015

                             A16                Deflection Amplifiers Assy                        03720-70016
                             A1 7               High Voltage Power Supply Assy                    03720-70017
                             A1 8               Range Indicator Assy                              03720-70018
                             A1 9               Range Units Assy                                  03720-70019
                             A20                Storage Assy                                      03720-70020


                                                                                                                    2-1


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Model 3720A



.2-10The MC number gives the physical location of        2-15 INSTRUMENT DISMANTLING
 each package in the form of a grid reference.


2-11 With the printed circuit board held compon-
                                                         I                     DANGER
                                                              115/230V AC AND +158V DC SUPPLY
ent side uppermost, and tongued connector near-
                                                              WIRES ARE EXPOSED WHEN ANY OF
est, numbering of the rows and columns of inte
                                                              THE INSTRUMENT COVERS ARE RE-
grated circuits starts from the top left hand corner
                                                              MOVED. USE EXTREME CAUTION DUR-
of the board. The first figure following the MC
                                                              ING TROUBLESHOOTING, ADJUSTMENT
prefix gives the row and the second gives the
                                                              OR REPAIR. AVOID DAMAGE TO THE
column. For example, MC52 will lie in the 5th
                                                              INSTRUMENT BY DISCONNECTING THE
row down and the 2nd column across, whilst
                                                              POWER CABLE BEFORE REMOVING OR
MC103 will be in the 10th row and 3rd column.
                                                              REPLACING COVERS, ASSEMBLIES OR
                                                              COMPONENTS.

2-12 The second method of identification of the
individual 'component blocks' helps the circuit          2-16 Removing Top and Bottom Covers
description and signal flow indication.
                                                         1.  Remove the four cross-head screws holding the
                                                                                                                 c
                                                             cover in position.
2-13 Each 'block' is given a prefix according t o        2. Slide the cover about l i n (2.5cm) t o the rear
its function (see Table 2-2 for a full list) and a           and lift clear.
number indicating i t s position on the schematic        NOTE: I t is not necessary to remove the feet or
diagram, in the same manner as resistors, capacitors,    the tilt stand from the bottom cover before
etc, are referenced.                                     remova I.


                                                         2-17 Removing Side Covers
Table 2-2 Digital integrated circuit abbreviations
                                                         1.    Remove the four cross-head screws securing
I      Abbreviation                      Function              each cover.
                                                         2.    Lift cover clear.
           B                          Buffer
           DD                         Decade Divider
           FF                         FIip-flop
                                                         2-18 Front Panel Access
           G                          Gate
           IG                         Inverter Gate
                                      Monostable         1.    Remove the top and bottom covers from the
           MS
                                      Sh if t Register         instru ment.
           SR
                                                         2.    Release the two screws securing the A l / A l l
                                                               retaining strip and lift this strip clear.
                                                         3.    Remove assemblies A2 to A1 1 inclusive.
                                                         4.    Release the two screws a t the base of each
2-14 All I C leads are referred to in the same way as
                                                               of the right hand and left hand board guides.
assembly connections. For example, lead 12 on
integrated circuit MC25, on A5 assembly, is              5.    Withdraw the board guides to give access to
referred t o as A5MC25(12). Similarly when de-                 the rear of the front panel.
scribing schematics, lead 6 on Flip-flop 9 on            6.    Re-assembly is a reversal of the above pro-
assembly A 2 would be referenced A2FF9(6).                     cedu re.

2-2


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                                                                                                               Section II



     2-19 MAINTENANCE                                         6.     Remove the four nuts holding the A18/A19
                                                                     housing assembly to the front panel. If
                                                                     necessary, gently move the wiring to gain
                                CAUTION                              access to the nuts.
                                                              7.     Release screw B shown in Figure 2-1.
          When handling the 3720A do not tilt the
                                                              8.     Holding the A18/A19 housing assembly with
          instrument onto its front panel.
                                                                     one hand, gently press the Display Sensi-
                                                                     tivity panel on the front of the instrument
                                                                     with the other hand to release the assembly.
     2-20 Locations of dc Power Supply Fuses                  9.     Replacement of the A1 8/A19 housing assem-
                                                                     bly is a reversal of the above procedure.

     2-21 Access t o the +158V, +50V, +15V, +5V, -15V,
     -22V and -5OV power supply fuses is gained by
     removing the bottom cover of the instrument.


     2-22 The +12.6V power supply fuse is on the A20
     Storage assembly. Access to the fuse is gained by
     removing the top cover of the 3720A.

     2-23 Replacement of Display Sensitivity Lamps

     2-24 The lamps are mounted on the A18 and A19
     assemblies. To replace the lamps the A18/A19
3    housing assembly must be removed from the
     instrument and then dismantled.


     2-25 Removal of A18/A19 Housing Assembly                             (                         103720 x O O 5 6 j



     1.    Remove the top cover, left side cover and                  Figure 2-1 A18/A19 Housing assembly
           fluted aluminium plate from the instrument.                           retaining screws
           Note that the fluted aluminium plate is self-
           adhesive.                                          2-26 Dismantling the A18/A19 Assembly

     2.     Release the two screws securing the A l / A l l   1.     Remove the A18/A19 housing assembly as
            retaining strip and lift this strip clear.               detailed i n Paragraph 2-25.
                                                              2.     Release the two screws holding the range
     3.    Remove assemblies A2 to A6 inclusive.                     units lamp separator in place.
                                                              3.     Slide the separator away from the assembly.
     4.    Release the two screws a t the base of the
           left hand board guide and withdraw the
           board guide.
                                                              I                    CAUTION
                                                                   If the separator is forced sideways the units
     5.    Remove the left hand board guide support
                                                                   lamps will be damaged.
           by releasing the three screws A shown in
.3         Figure 2-1.
                                                                                                                         2-3



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Model 372QA



4.    Pull out A18 and/or A19 assemblies as re       12. Remove the black light shield surrounding
      quired and disconnect the A18/A19 inter-           the CRT screen by gently squeezing i t a t the
      connecting cables.                                 top centre and bottom centre and pulling
5.    Renew the faulty lamps.                            clear.
6.    Re-assembly is a reversal of the above pro-    13. Unscrew and remove the bezel.
      cedu re.                                       14. Slacken theclamp on the rear of the CRT neck.
                                                     15. Holding the screen of CRT with one hand,
                                                         gently press the rear of the tube with the
2-27 Cleaning The Air Filter                             other hand and slide the CRT forward and
                                                         out.

2-28 The air filter on the fan cover of the 3720A    NOTE: To prevent accidental damage to the
should be removed periodically for cleaning. Four    storage mesh DO NOT TILT THE CRT FACE
screws secure the fan cover t o the back panel.      DO WNWARDS.

                                                     16. Re-assembly is a reversal of the above pro-
2-29 Cathode Ray Tube Removal/Replacement                cedure.



                      DANGER
     WHEN HANDLING THE CRT ALWAYS
     WEAR GOGGLES AND GLOVES. HANDLE
     WITH EXTREME CARE.
                                                          1 A16   DEFLECTION AMPLIFIERS ASSY              I
1.  Disconnect the power cable from the 3720A
2.  Remove the top cover from the instrument.
3.  Remove the back panel high voltage cover.
4.  Unplug the CRT socket.
5.  Release the two screws holding A20 in
    place and lift out A20.
6. Unplug the wires connected t o the neck
    of the CRT. The colours of the wires are
    shown in Figure 2-2.
7. Remove AZO support block by releasing
    the two screws which hold it in place.
8. Release the two screws securing the A l / A l l           cu    CR3
    retaining strip and lift this strip clear.
9. Remove assemblies A2 t o A6 inclusive.
10. Remove the two screws holding the high
    voltage connector A55J1 in place. Disconnect
    the flexible wiring from this connector.
11. Unplug the wire from the collimator conn-
    ector on the side of the CRT.                            Figure 2-2 CRT neck connections

2-4                                                                                                       1


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                                                                                                 Section I1



2-30 Line Transformer Removal/Replacement              2.   Remove the internal high voltage cover.

 1.   Tilt the 3720A onto its right hand side.         3.   Remove the rear panel high voltage cover.

2.    Remove the top and bottom covers from the        4.   Unplug the five wires from A17 and then
                                                            remove A1 7.
      instrument.
3.                                                     5.   Unsolder the black and grey wires from the
      Release the two screws holding A20 in place
                                                            ground tag.
      and lift out A20.
                                                       6.   Release the two screws holding A20 in place
.4.   Remove the back panel high voltage cover.
                                                            and lift out A20.
5.    Remove the internal high voltage cover.
                                                       1.   Remove XA20 mounting plate.
6.    Unplug the five wires from A17 and then
                                                       8.   Release the two screws securing the A l / A l l
      remove A I 7.
                                                            retaining strip and lift this strip clear.
7.    Remove XA20 mounting plate and pull it
                                                       9.   Remove assemblies A2 to A6 inclusive.
      gently to the side.
                                                       10: Remove A20 support block. Two screws
8. Note the wire colours against the corres-
                                                           hold it in place.
      ponding pin numbers on the top and bottom
      of the line transformer and then unsolder        11. Remove the two screws holding the high
      the connections.                                     voltage connector A55J1 in place. Disconnect
                                                           the flexible wiring from this connector.
9.    Remove the four screws holding the trans-
      former in position. Retain the underside         12. Unsolder the wires from XA(20(L) and
      nuts and safety mouldings and pull the trans-        XA20(N) after noting their colours.
      former out through the top of the instrument.
                                                       13. Remove the wires from the grommet.
10. Re-assembly is a reversal of the above pro-
                                                       14. Lift out the high voltage tripler assembly.
    cedure.
                                                       15. Re-assembly is a reversal of the above pro-
2-31 Chassis Mounted Transistors Plate                     cedu re.
Removal/Replacement
1.    Remove the top cover and right side cover
                                                       2-33 REPAIR PROCEDURES
      from the instrument.
2.    Release the two screws securing the A12/
      A16 retaining strip and lift this strip clear.   2-34 Etched Circuits

3.    Remove assemblies A12 to A16 inclusive.          2-35The etched circuit boards in the Spectrum
4. Release the two screws a t the bottom of the        Display are of the plated-through type, consisting
                                                       of metallic conductors bonded to both sides of the
      transistor plate.
                                                       insulating material. The metallic conductors are
5.    Withdraw the plate.                              extended through the component mounting holes
                                                       by a plating process. Solder connection can be
6.    Renew the faulty transistors as necessary.       made from either side of the board with equally
7.    Re-assembly is a reversal of the above pro-      good results. Following are recommendations and
      cedure.                                          precautions pertinent to etched circuit repair
                                                       work :
2-32 High Voltage Tripler Assembly Removal/
Replacement                                            a.   Avoid unnecessary component substitution;
                                                       it can result in damage to the circuit board and/or
1.    Remove the top cover from the instrument.        adjacent components.
                                                                                                       2-5

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Model 3720A



b. D o ' n o t use a high-power soldering iron on       removing integrated circuit packages from a printed
etched circuit boards. Excessive heat may lift a        circuit board:
conductor or damage the board. A 40 watt solder-
ing iron is sufficient.                                 a.   Solder Gobbler. This is the best method.
                                                        Solder is removed from the board by a soldering
c.   Use a suction device, eg, Soldapult, or wooden     iron with a hollow tip connected t o a vacuum
toothpick to remove solder from component               source. This permits an IC to be removed intact
mounting holes. Care must be i3ken when clear-          so that it may be replaced if an error has been
ing out component mounting holes; never use             made in diagnosis.
sharp metal objects, such as an awl or a twist-drill,
which could damage the plated-throughconductor.

d. After soldering, remove excess flux from the         b. Desoldering Tool. (Soldapult - hp Part No.
soldered areas with a soac and water solution.          8690-0060). This method is recommended if a
                                                        vacuum operated Solder Gobbler is not available.
e.   When removing a multiple connection com-           Remove the solder from each lead by using the
ponent, such as an integrated circuit, loosen           soldering iron and the desoldering tool together.
it gradually, using a gentle side-to-side motion,
to avoid damage to the plated-throughconductors.

                                                        c.    Clip Out. This is the least satisfactory of the
2-36 Integrated Circuit Removal/Replacement             three methods. Clip the leads as close to the case
                                                        as possible. With a soldering iron and long nose
2-37 There are three recommended methods of             pliers carefully remove the leads from each hole.




2-6

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                                                                                                         Section I I I



                                                   SECTION 111
                                         REPLACEABLE PARTS
    3-1 INTRODUCTION



    3-2 This section contains information for ordering replaceable parts. Table 3-1 lists parts in alpha-
    numerical order of their reference designators and gives the following information for each part:
    a.    Hewlett-Packard stock number.
    b.    Description (abbreviations given in Paragraphs 3-7, 3-8 and 3-9).
    c.    Total quantities of each part used in the instrument (refer to TQ column).
    d.    Manufacturer and Manufacturer's part number (Code List of Manufacturers given in Table 3-2).



1
    3-3 ORDERING INFORMATION

J

    3-4 To order a replacement part, address the order or enquiry to your local Hewlett-Packard Sales and
    Service Office (addresses are listed a t the rear of this manual).



    3-5 Specify the following information for each part:
    a.    Model and full serial number of instrument.
    b.    Hewlett-Packard stock number.
    c.    Circuit reference designator.
    d.    Description.



    3-6 To ocder a part not listed in the tables, give a complete description of the part including its function
    and location in the instrument.




    3-7 REFERENCE DESIGNATORS

    A       = assembly                       L          = inductor                     S       -= switch
    C       = capacitor                      MC         = micro circuit                SR      = shift register
    CR      =diode                           MP         = metal work/                  T       = transformer
    DS      =lamp                                         miscellaneous part           XA      = printed circuit
    F       = fuse                           P          = plug (male)                            board edge
    IC      = integrated circuit             0          = transistor                             connector
    J '     = connector (female)             R          = resistor

                                                                                                                3-1

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Model 3720A



3-8 LIST OF ABBREVIATIONS



A       = ampere                                   INCD = incandescent                                  QUAD = quadruple
AC      = alternating                              IND = inductor                                       REC = rectifier
         current                                   INV = invert                                         RH   = right hand
AL     = aluminium                                 I/P  = input
                                                                                                               side
AMPL   = amplifier                                 K    = kilo ( lo3)                                   RND =round
ASSY   = assembly                                  LED = light emitting diode                           RTRY = rotary
BD     = board                                     LH   = left hand side
                                                                                                        SI   = si I icon
BHD    = bulkhead                                  LIN = linear                                         SPDT = single pole,
                                                                                                               double throw
BKDN   = breakdown                                 LVR = lever
CBL    = cable
                                                                                                        SPST = single pole,
                                                   M    = mega ( 1O6 )
                                                                                                               single throw
COAX   = coaxial                                   MA   = milli ampere
                                                                                                        SW   =switch
COMP   = compensated                               MH   = milli henry
                                                                                                        T    = throw
CONCEN = concentric                                MTG = mounting
                                                                                                        TEMP = temperature
CONN   = connector                                 MW   = milli watt
                                                                                                        TGL = toggle
CONT   = controlled                                NAND = not and
                                                                                                        TQ"  = total quantity
CRT    = cathode ray tube                          NOR = n o t o r
                                                                                                        UF   = micro farad
DIO    = diode                                     NPN = negative-positive-                                         (10-6)
DPDT   = double pole,                                      negative
                                                                                                        V      = volt
         double throw                              NSR = not separately
                                                           repIaceable                                  VAR    = variable
FET    = field effect
         transistor                                OPER = operational                                   W      = watt
FXD    = fixed                                     PC   = printed circuit
                                                                                                        WVDC   = working voltage
                                                                                                               d irect cu rrent
GE     = germanium                                  PF  = pic0 farad ( 1O-'*
                                                                                                        XFMR = transformer
HV     = high voltage                               PIV = peak inverse volts
       = high speed
                                                                                      



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