Tektronix TDS 520B Service Manual
TDS 520B Mod CM
Digitizing Oscilloscope
Component Service Manual
070-9710-03
First Edition: May 30, 1996
Revised: February 26, 1998
Serial Numbers: B030000 and above
Warning
The servicing instructions are for use by qualified
personnel only. To avoid personal injury, do not
perform any servicing unless you are qualified to
do so. Refer to all safety summaries prior to
performing service.
Copyright T ektronix, Inc. 1996. All rights reserved.
T ektronix products are covered by U.S. and foreign patents, issued and pending. Information in this publication supercedes
that in all previously published material. Specifications and price change privileges reserved.
Printed in the U.S.A.
T ektronix, Inc., P.O. Box 1000, Wilsonville, OR 97070–1000
TEKTRONIX and TEK are registered trademarks of T ektronix, Inc.
Pursuant to DFARS 252.227-7013(e), Tektronix Inc. hereby grants to the Government a nonexclusive, paid-up license
throughout the world of the scope set forth therein for Government purposes for any commercial manuals provided by
T ektronix Inc. under this contract.
WARRANTY
T ektronix warrants that this product will be free from defects in materials and workmanship for a period of three (3) years
from the date of shipment. If any such product proves defective during this warranty period, T ektronix, at its option, either
will repair the defective product without charge for parts and labor, or will provide a replacement in exchange for the
defective product.
In order to obtain service under this warranty, Customer must notify Tektronix of the defect before the expiration of the
warranty period and make suitable arrangements for the performance of service. Customer shall be responsible for
packaging and shipping the defective product to the service center designated by T ektronix, with shipping charges prepaid.
T ektronix shall pay for the return of the product to Customer if the shipment is to a location within the country in which the
T ektronix service center is located. Customer shall be responsible for paying all shipping charges, duties, taxes, and any
other charges for products returned to any other locations.
This warranty shall not apply to any defect, failure or damage caused by improper use or improper or inadequate
maintenance and care. T ektronix shall not be obligated to furnish service under this warranty a) to repair damage resulting
from attempts by personnel other than T ektronix representatives to install, repair or service the product; b) to repair
damage resulting from improper use or connection to incompatible equipment; or c) to service a product that has been
modified or integrated with other products when the effect of such modification or integration increases the time or
difficulty of servicing the product.
THIS WARRANTY IS GIVEN BY TEKTRONIX WITH RESPECT TO THIS PRODUCT IN LIEU OF ANY
OTHER WARRANTIES, EXPRESSED OR IMPLIED. TEKTRONIX AND ITS VENDORS DISCLAIM ANY
IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
TEKTRONIX’ RESPONSIBILITY TO REPAIR OR REPLACE DEFECTIVE PRODUCTS IS THE SOLE AND
EXCLUSIVE REMEDY PROVIDED TO THE CUST OMER FOR BREACH OF THIS WARRANTY. TEKTRONIX
AND ITS VENDORS WILL NOT BE LIABLE FOR ANY INDIRECT , SPECIAL, INCIDENTAL, OR
CONSEQUENTIAL DAMAGES IRRESPECTIVE OF WHETHER TEKTRONIX OR THE VENDOR HAS
ADVANCE NOTICE OF THE POSSIBILITY OF SUCH DAMAGES.
Table of Contents
Theory of Operation
Maintenance
General Safety Summary v. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Service Safety Summary ix. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Preface xi. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Logic Conventions 1–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Module Overview 1–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Detailed Circuit Description 1–5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Acquisition System A10 1–5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Processor System A11 1–17. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Display System A11 1–22. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Firmface A11 1–27. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Front Panel A12 1–27. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
D1 Bus D14 1–29. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Low Voltage Power Supply A16 1–29. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Display Driver Board A20 1–31. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Memory Maps 1–37. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Firmware Reprogramming 2–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Minimum Tool & Equipment List 2–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Instructions 2–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Storage and Shipment Instructions 2–7. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Instructions 2–7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Specifications 2–8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Replaceable Electrical Parts
Replaceable Electrical Parts 3–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Replaceable Mechanical Parts
Replaceable Mechanical parts 4–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Diagrams and Circuit Board Illustrations
Diagrams and Circuit Board Illustrations 5–1. . . . . . . . . . . . . . . . . . . . . .
Symbols 5–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Component Values 5–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Graphic Items and Special Symbols Used in This Manual 5–1. . . . . . . . . . . . . . . . .
Component Locator Diagrams 5–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
TDS 520B Mod CM Component Service Manual
i
Table of Contents
List of Figures
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 2–1: PC & TDS Setup 2–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 2–2: Selecting the I/O system in the Main Menu 2–2. . . . . . . . . . .
Figure 2–3: Accessing the Protection Switch 2–5. . . . . . . . . . . . . . . . . . . .
Figure 4–1: Cabinet 4–7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 4–2: Front 4–9. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 4–3: Chassis and rear 4–11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 4–4: Circuit boards 4–13. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 4–5: LV Power Supply 4–15. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 4–6: Accessories 4–17. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 5–1: A10 Acquisition board front (section A) 5–2. . . . . . . . . . . . . .
Figure 5–2: A10 Acquisition board front (section B) 5–3. . . . . . . . . . . . . .
Figure 5–3: A10 Aquisition board front (section C) 5–4. . . . . . . . . . . . . . .
Figure 5–4: A10 Acquisition board front (section D) 5–5. . . . . . . . . . . . . .
Figure 5–5: A10 Acquisition board back (section A) 5–6. . . . . . . . . . . . . .
Figure 5–6: A10 Aquisition board back (section B) 5–7. . . . . . . . . . . . . . .
Figure 5–7: A10 Acquisition board back (section C) 5–8. . . . . . . . . . . . . .
Figure 5–8: A10 Acquisition board back (section D) 5–9. . . . . . . . . . . . . .
Figure 5–9: A10 Aquisition component locator 5–10. . . . . . . . . . . . . . . . . .
Figure 5–10: A10 Aquisition component locator (Cont.) 5–11. . . . . . . . . . .
Figure 5–11: A11 Processor board (section A) 5–66. . . . . . . . . . . . . . . . . . .
Figure 5–12: A11 Processor board (section B) 5–67. . . . . . . . . . . . . . . . . . .
Figure 5–13: A11 Processor board (section C) 5–68. . . . . . . . . . . . . . . . . . .
Figure 5–14: A11 Processor board (section D) 5–69. . . . . . . . . . . . . . . . . . .
Figure 5–15: A11 Processor component locator 5–70. . . . . . . . . . . . . . . . . .
Figure 5–16: A11 Processor component locator (Cont.) 5–71. . . . . . . . . . .
Figure 5–17: A12 Front Panel board front 5–126. . . . . . . . . . . . . . . . . . . . . .
Figure 5–18: A12 Front Panel board back 5–127. . . . . . . . . . . . . . . . . . . . . .
Figure 5–19: A12 component locator 5–128. . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 5–20: A14 D1 Bus board 5–136. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 5–21: A17 RBL Mother board (sections A, B) 5–138. . . . . . . . . . . . .
Figure 5–22: A17 RLB Mother board (sections C, D) 5–139. . . . . . . . . . . . .
Figure 5–23: A17 RLB Mother component locator 5–140. . . . . . . . . . . . . . .
ii
TDS 520B Mod CM Component Service Manual
Table of Contents
Figure 5–24: A18 TBL Secondary Monitor board 5–146. . . . . . . . . . . . . . . .
Figure 5–25: A20 CRT Driver board 5–150. . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 5–26: A20 component locator 5–151. . . . . . . . . . . . . . . . . . . . . . . . . . .
TDS 520B Mod CM Component Service Manual
iii
Table of Contents
List of Tables
Table 1-1: Relay Driver Control Data (CD) Bit Pattern 1-6..........
Table 1-2: Bandwidth Limit Selection Bits(Cont.) 1-8...............
Table 1-3: Gain Set Bits 1-8....................................
Table 1-4: Preamps to Track/Hold Input 1-9......................
Table 1-5: Track/Hold Outputs to A/D Input 1-9...................
Table 1-6: Preamps to Track/Hold Input 1-10......................
Table 1-7: 68020 Memory Map 1-37..............................
Table 1-8: Kernel Memory Map (0000 0000 to 00FF FFFF)
All 8 Bits Wide 1-38.........................................
Table 1-9: Bus Control Register (0040 0000 R/W) 1-38..............
Table 1-10: 7 Segment LED (0060 0000 Write Only) 1-39............
Table 1-11: DSP Interrupt Mask Register 1-40.....................
Table 1-12: DSP Interrupt Read Register 1-40.....................
Table 1-13: DSP Memory Map 1-41..............................
Table 1-14: D2MMIO Miscellaneous Register 1-42.................
Table 1-15: 68020 to DSP Instruction Memory Accesses 1-42.........
Table 1-16: Display Memory Map 1-43............................
Table 1-17: BDSACK Combinations For 68020 Memory Space
1-45......................................................
Table 1-18: A11 DRAM Processor/Display Wait State
Generation 1-46............................................
Table 1-19: A11 DRAM Processor/Display DUART Interface
Signals 1-47................................................
Table 1-20: A10 Acquisition Demultiplexer DB Memory Map 1-48....
Table 1-21: Device Interrupt Levels 1-49..........................
Table 1-22: Interrupt Mask Register 0900 0000 (R/W) 1-49..........
Table 1-23: Miscellaneous Register 0920 0000 (R/W) 1-50............
Table 1-24: Interrupt Read Register 1 0940 0000 (Read Only) 1-50....
Table 1-25: Interrupt Read Register 2 0960 0000 (Read Only) 1-51....
Table 1-26: Troubleshooting Procedure For LED Display 1-52........
Table 1-27: DIP Switch Options 1-53.............................
Table 1-28: A11 DRAM Processor/Display LED (DS1) 1-54..........
Table 2–1: Characteristics — Environmental 2–8. . . . . . . . . . . . . . . . . . .
iv
TDS 520B Mod CM Component Service Manual
General Safety Summary
Review the following safety precautions to avoid injury and prevent damage to
this product or any products connected to it. To avoid potential hazards, use the
product only as specified.
Only qualified personnel should perform service procedures.
Injury Precautions
Use Proper Power Cord
Avoid Electric Overload
Ground the Product
Do Not Operate Without
Covers
Use Proper Fuse
Do Not Operate in
Wet/Damp Conditions
Do Not Operate in
Explosive Atmosphere
To avoid fire hazard, use only the power cord specified for this product.
To avoid electric shock or fire hazard, do not apply a voltage to a terminal that is
outside the range specified for that terminal.
This product is grounded through the grounding conductor of the power cord. To
avoid electric shock, the grounding conductor must be connected to earth
ground. Before making connections to the input or output terminals of the
product, ensure that the product is properly grounded.
To avoid electric shock or fire hazard, do not operate this product with covers or
panels removed.
To avoid fire hazard, use only the fuse type and rating specified for this product.
To avoid electric shock, do not operate this product in wet or damp conditions.
To avoid injury or fire hazard, do not operate this product in an explosive
atmosphere.
Keep Probe Surface Clean
To avoid electric shock and erroneous readings, keep probe surface clean.
Product Damage Precautions
Use Proper Power Source
TDS 520B Mod CM Component Service Manual
Do not operate this product from a power source that applies more than the
voltage specified.
v
General Safety Summary
Use Proper Voltage
Setting
Provide Proper Ventilation
Do Not Operate With
Suspected Failures
Do Not Immerse in Liquids
Before applying power, ensure that the line selector is in the proper position for
the power source being used.
To prevent product overheating, provide proper ventilation.
If you suspect there is damage to this product, have it inspected by qualified
service personnel.
Clean the probe using only a damp cloth. Refer to cleaning instructions.
Safety Terms and Symbols
Terms in This Manual
These terms may appear in this manual:
WARNING. Warning statements identify conditions or practices that could result
in injury or loss of life.
Terms on the Product
CAUTION. Caution statements identify conditions or practices that could result in
damage to this product or other property.
These terms may appear on the product:
DANGER indicates an injury hazard immediately accessible as you read the
marking.
WARNING indicates an injury hazard not immediately accessible as you read the
marking.
CAUTION indicates a hazard to property including the product.
vi
TDS 520B Mod CM Component Service Manual
General Safety Summary
Symbols on the Product
The following symbols may appear on the product:
DANGER
High Voltage
Certifications and Compliances
CSA Certified Power
Cords
CSA Certification includes the products and power cords appropriate for use in
the North America power network. All other power cords supplied are approved
for the country of use.
Protective Ground
(Earth) T erminal
ATTENTION
Refer to
Manual
Double
Insulated
TDS 520B Mod CM Component Service Manual
vii
General Safety Summary
viii
TDS 520B Mod CM Component Service Manual
Service Safety Summary
Only qualified personnel should perform service procedures. Read this Service
Safety Summary and the General Safety Summary before performing any service
procedures.
Do Not Service Alone
Disconnect Power
Use Caution When
Servicing the CRT
Use Care When Servicing
With Power On
Do not perform internal service or adjustments of this product unless another
person capable of rendering first aid and resuscitation is present.
To avoid electric shock, disconnect the main power by means of the power cord
or, if provided, the power switch.
To avoid electric shock or injury, use extreme caution when handling the CRT.
Only qualified personnel familiar with CRT servicing procedures and precautions
should remove or install the CRT.
CRTs retain hazardous voltages for long periods of time after power is turned off.
Before attempting any servicing, discharge the CRT by shorting the anode to
chassis ground. When discharging the CRT, connect the discharge path to ground
and then the anode. Rough handling may cause the CRT to implode. Do not nick
or scratch the glass or subject it to undue pressure when removing or installing it.
When handling the CRT, wear safety goggles and heavy gloves for protection.
Dangerous voltages or currents may exist in this product. Disconnect power,
remove battery (if applicable), and disconnect test leads before removing
protective panels, soldering, or replacing components.
To avoid electric shock, do not touch exposed connections.
X-Radiation
TDS 520B Mod CM Component Service Manual
To avoid x-radiation exposure, do not modify or otherwise alter the high-voltage
circuitry or the CRT enclosure. X-ray emissions generated within this product
have been sufficiently shielded.
ix
Service Safety Summary
x
TDS 520B Mod CM Component Service Manual
Preface
Manual Structure
This preface contains information needed to properly use this manual to service
the TDS 520B Digitizing Oscilloscope, as well as general information critical to
safe and effective servicing of this oscilloscope.
This manual is divided into sections, such as Theory of Operation and Parts
Lists. Further, it is divided into subsections, such as Product Description and
Removal and Installation Procedures.
Sections containing procedures also contain introductions to those procedures.
Be sure to read these introductions because they provide information needed to
do the service correctly and efficiently. The following is a brief description of
each manual section.
H Theory of Operation contains circuit descriptions that support general service
and fault isolation down to the module level.
H Electrical Parts List contains a statement referring you to Mechanical
Replaceable Parts, where both electrical and mechanical modules are listed.
Manual Conventions
Modules
H Mechanical Parts List includes a table of all replaceable modules, their
descriptions, and their Tektronix part numbers.
H Schematics contains schematic diagrams of the various circuit boards in the
TDS 520B.
H Dollies contains diagrams of the various circuit boards in the TDS 520B.
This manual uses certain conventions which you should become familiar with
before doing service.
Throughout this manual, any replaceable component, assembly, or part of these
Digitizing Oscilloscope is referred to generically as a module. In general, a
module is an assembly, like a circuit board, rather than a component, like a
resistor or an integrated circuit. Sometimes a single component is a module; for
example, each chassis part of the oscilloscope is a module.
TDS 520B Mod CM Component Service Manual
xi
Preface
Safety
Symbols
Related Manuals
Symbols and terms related to safety appear in the Safety Summary found at the
beginning of this manual.
Besides the symbols related to safety, this manual uses the following symbols:
STOP. The stop labels information which must be read in order to correctly do
service and to avoid incorrectly using or applying service procedures.
The clock icon labels procedure steps which require a pause to wait for
the oscilloscope to complete some operation before you can continue.
Various icons such as the example icon at the left are used in procedures
to help identify certain readouts and menu functions on screen.
The TDS 520B Digitizing Oscilloscope, Option CM comes with the following
manuals:
TDS 520B, TDS 540B, TDS 620B, TDS 644B, TDS 680B, TDS 684B, TDS 724A,
TDS 744A, & 784A User Manual (Tektronix part number 070-9383-XX)
contains a tutorial to quickly show you how to operate the TDS 520B Digitizing
Oscilloscope and an in depth discussion of how to more completely use their
features. Applications are also discussed.
TDS 520B, TDS 540B, TDS 620B, TDS 644B, TDS 680B, TDS 684B, TDS 724A,
TDS 744A, & TDS 784A Reference (Tektronix part number 070-9382-XX)
contains a brief overview of oscilloscope operation.
TDS Family (400A, 500B, 600B, and 700A) Programmer Manual (Tektronix part
number 070-9556-XX) contains information for programmed operation via the
GPIB interface. Included are the complete command set, setup information, and
programming examples.
TDS 520B, TDS 540B, TDS 620B, TDS 644B, TDS 680B, TDS 684B, TDS 724A,
TDS 744A, & TDS 784A Technical Reference (Tektronix part number
070-9384-XX) contains performance verification procedures and specifications.
TDS 520B, TDS 540B, TDS 620B, TDS 644B, TDS 680B, TDS 684B, TDS 724A,
TDS 744A, & TDS 784A Service (Tektronix part number 070-9386-XX) contains
repair procedures to the modular level.
xii
TDS 520B Mod CM Component Service Manual
Theory of Operation
Theory of Operation
This section describes the electrical operation of the TDS 520B Digitizing
Oscilloscope. First, an overview discussion, based on the block diagram, gives
an overall view of the module design. Next, a detailed circuit description, based
on the schematic diagrams in Section 5, gives a more detailed view. These
descriptions, together with the troubleshooting information in the TDS 500B,
600B, and 700A Service Manual, Tektronix part number 070-9386-01, should
enable a qualified technician with the appropriate test equipment to isolate a
problem to the appropriate level.
This section has three main parts:
H Logic Conventions describes how logic functions are discussed and
represented in this manual.
H Module Overview describes circuit operation from a functional-circuit block
perspective.
H Detailed Circuit Description provides detailed information about TDS
520B Digitizing Oscilloscope hardware with reference to the numbered
schematics in Section 3.
Logic Conventions
Module Overview
The Digitizing Oscilloscope contain many digital logic circuits. This manual
refers to these circuits with standard logic symbols and terms. Unless otherwise
stated, all logic functions are described using the positive-logic convention: the
more positive of the two logic levels is the high (1) state, and the more negative
level is the low (0) state. Signal states may also be described as “true” meaning
their active state or “false” meaning their nonactive state. The specific voltages
that constitute a high or low state vary among the electronic devices.
Active-low signals are indicated by a tilde prefixed to the signal name
(~RESET). Signal names are considered to be either active-high, active-low, or
to have both active-high and active-low states.
This module overview describes the basic operation of each functional circuit
block as shown in Diagram
. Figure 5-2.
TDS 520B Mod CM Component Service Manual
1–1
Theory of Operation
General
Input Signal Path
The TDS 520B Digitizing Oscilloscope is a portable two-channel instrument.
Each channel provides a calibrated vertical scale factor.
A signal enters the oscilloscope through a probe connected to a BNC on the A10
Attenuator/Acquisition board.
Attenuators. Circuitry in the attenuator selects the input coupling, termination,
and the attenuation factor. The processor system, by way of the acquisition
system, controls the attenuators. For example, if 50 input termination is
selected and the input is overloaded, the processor system switches the input to
the 1 M position.
Probe Coding Interface. Probe coding interface signals pass through the attenuator
portion of the A10 Attenuator/Acquisition to the acquisition system, where they
are sensed and controlled.
Acquisition System. The acquisition system amplifies the input signals, samples
them, converts them to digital signals, and controls the acquisition process under
direction of the processor system. The acquisition system includes the trigger,
acquisition timing, and acquisition mode generation and control circuitry.
D1 Bus. The acquisition system passes the digital values representing the
acquired waveform through the A14 D1 Bus to the A11 DRAM Processor/Display board. This happens after a waveform acquisition is complete if the digital
signal processor in the processor system requests the waveform.
Processor System. The processor system contains a 68020 microprocessor that
controls the entire instrument. This system also includes the firmware and a
GPIB interface. You can reprogram the firmware from a remote controller using
the GPIB and an external software package.
The processor also includes a digital signal processor. This signal processor
processes each waveform as directed by the system processor. Waveforms and
any text to be displayed are passed on to the display system. The A11 DRAM
Processor/Display board contains both the processor and display systems.
Display System. Text and waveforms are processed by different parts of the
display circuitry. The display system sends the text and waveform information to
the tube assembly as a video signal. The display system also generates and sends
vertical (VSYNC) and horizontal (HSYNC) sync signals to the tube assembly. A
VGA-compatible video output is at the rear of the TDS 520B.
1–2
TDS 520B Mod CM Component Service Manual
Theory of Operation
Tube Assembly
Front Panel
Rear Panel
All information (waveforms, text, graticules, and pictographs) is displayed by
the A20 Display system. The A20 generates the high voltages necessary to drive
the display tube. It also contains the video amplifier, horizontal oscillator, and
the vertical and horizontal yoke driver circuitry.
The processor system sends instructions to and receives information from the
Front Panel Processor on the A12 Front Panel board. The Front Panel Processor
reads the front-panel switches and potentiometers. Any changes in their settings
are reported to the processor system. The Front Panel Processor also turns the
LEDs on and off and generates the bell signal.
Front-panel menu switches are also read by the Front Panel Processor. The
processor sends any changes in menu selections to the processor system. The
ON/STBY switch is one of the menu switches. However, it is not read by the
Front Panel Processor, but passes through the A12 Front Panel board and the
A11 DRAM Processor/Display board to the low voltage power supply.
The front panel also generates the probe compensation signals SIGNAL
and GND.
The GPIB connector provides access to stored waveforms, and allows external
control of the oscilloscope. Other rear panel connectors are the AUX TRIGGER
INPUT, MAIN and DELAYED TRIGGER OUTPUT, and a CHANNEL 3
SIGNAL OUTPUT.
Low Voltage Power Supply
Fan
You can make hardcopies on the GPIB port. If your TDS 520B has the optional
RS-232 and Centronics ports, you can also use those.
The low voltage power supply is a switching power converter with active power
factor control. It supplies power to all of the circuitry in the oscilloscope.
The principal POWER switch, located on the rear panel, controls all power to
the oscilloscope including the Low Voltage Power Supply. The ON/STBY
switch, located on the front panel, also controls all of the power to the oscilloscope except for part of the circuitry in the Low Voltage Power Supply.
The power supply sends a power fail (~PF) warning to the processor system if
the power is going down.
The fan provides forced air cooling for the oscilloscope. It connects to +25 V
from the Low Voltage Power Supply by way of the A11 DRAM Processor/Display module.
TDS 520B Mod CM Component Service Manual
1–3
Theory of Operation
1–4
TDS 520B Mod CM Component Service Manual
Detailed Circuit Description
This detailed circuit description describes the operation of the oscilloscope
circuitry shown in schematic diagrams in the Diagrams section. While reading
this description, refer to the block diagrams and the schematic diagrams in the
Diagrams section.
Acquisition System A10
The A10 Acquisition board amplifies, via the attenuator assembly, and acquires
the analog signal. The acquisition system converts the signal to digital and stores
it in acquisition memory. Acquisition and trigger control circuitry controls the
acquisition process. DSP and the 68020 monitor and control the overall system,
and transfer the acquired waveform to the display system.
Attenuators A10
3
4 5 6
The attenuator assembly contains four attenuator hybrids, see Figure 1–1, and
four probe connectors. Each attenuator hybrid contains resistive dividers, an AC
coupling capacitor, relays, a 50 terminator, a buffer amplifier, and a preamp.
The outputs of the attenuator assembly (the preamp output) drive the track and
hold.
BNC
1
Resistive
dividers
1
Buffer Preamp
10
Figure 1–1: Attenuator hybrid
From here on the theory refers only to Ch4. The other channels work in similar
ways.
TDS 520B Mod CM Component Service Manual
100
Gain and
BW controls
1–5
Detailed Circuit Description
Mode
The 68020 interprets user commands and initiates changes to the settings. The
Acquisition Processor monitors the input overload sense (OVLS1–OVLS4) and
the probe data (PRDATA1–PRDATA4) communication lines.
Each attenuator hybrid has five relays. One or more of the relays must be turned
on if a signal is to pass from the BNC to the output of the attenuator.
The AC/DC coupling relay couples the output of the BNC to the other relays in
the attenuator hybrid. For AC signals, the AC/DC coupling relay inserts a
coupling capacitor into the input signal path.
When active, the 1 M/50 relay terminates the input in 50 .
A relay driver (U1102, sheet 6) selects an attenuator’s attenuation factor by
connecting one of its relays to the input BNC, and connecting all of its other
relays to the ATTNCAL adjustment signal.
When ATTENSTB goes high, all attenuators enter their inactive state. Attenuator
clock CCATTN clocks control data (DIN, U1102, pin 3) from the processor
system into the attenuator Relay Driver. With a new pattern in the Relay Driver,
the processor system sets ATTENSTB low, enabling the attenuators.
The serial data line (DIN, U1102, pin 3) comes from sheet 21, U1050, pin 27.
The strobe (ATTENSTB, U1102, pin 8) comes from sheet 21, U1050 pin 11
(SCLK2). The DOUT line (U1102, pin 6) feeds the shifted data to the Ch3 relay
driver, where it becomes DIN for Ch3 (U1202, pin 3). This continues until Ch1.
After Ch1, the DOUT pin (sheet 3, U1402, pin 6) is sent back to sheet 21,
U1050, pin 6. By feeding the serial data back to the control IC (U1050), the
system can perform diagnostics on the serial data path.
T able 1–1: Relay Driver Control Data (CD) Bit Pattern
Bit
7 6 2 8 5 4 1 3
AC 1 NC
DC 0 NC
50 NC
1 M NC
1X BNC NC
10X BNC NC
100X BNC NC
1
1
1
1
1
1 NC
0 NC
NC
NC
NC
1
1
1
1
1
NC
NC
1
1
1
1
NC
NC
NC
NC
1
1
1
1
NC
NC
NC
NC
1
1
1
1
NC
NC
NC
NC
1
1
1
1
NC
NC
NC
NC
1
1
1
1
1 0 0 1 0 0
0 1 0 0 1 0
0 0 1 0 0 1
NC
NC
NC
NC
1
1
1
1
1–6
OFF 0 0 0 0 0 0 0 1
1XCAL NC
10XCAL NC
1
1
NC
NC
1
0 0 0 1 0 0
1
0 0 0 0 1 0
TDS 520B Mod CM Component Service Manual
Detailed Circuit Description
T able 1–1: Relay Driver Control Data (CD) Bit Pattern (Cont.)
Bit
Mode
Mode 31458267
100XCAL NC
INACTIVE 0 0 0 0 0 0 0 0
1
NC equals no change.
1
NC
1
0 0 0 0 0 1
Preamps A10
3
4 5 6
Since the preamp circuitry for each preamp is similar, only the circuitry for
Preamp 4 is described. Preamp 4 provides gain switching, bandwidth limit
7
filters, and outputs for the display, trigger, and other signal paths.
The system processor controls the Preamp 4 functions. It sends commands over
serial data line.
The Analog DAC Control system provides DC voltage signals that set the
Preamp offset. The Acquisition Processor (U600) stores the digital values of
each of the voltage levels in digital-to-analog converter (DAC) U900. The
Acquisition Processor transfers each voltage through DAC Multiplexer U934 to
Preamp 4. Preamp variable gain, HF adjust, fine offset and balance controls are
controlled by the daculator (U904) which is controlled by the GTL (U1050) via
the serial data bus (SDOUT U1050).
Preamp 4 Control Buffers. (sheet 6) The Preamp 4 Control Buffers provide offset,
balance, variable gain, and high frequency compensation voltages for the
preamp.
The offset control voltage is sampled by U934 (sheet 26) and held on capacitor
C1101. U1405 buffers the hold voltage so it can be fed into the attenuator hybrid
and then to the preamp. Fine offset and balance controls do not need a hold cap
because they come from the daculator (U904) which internally holds the
voltages. Fine offset and balance are buffered by U1101 and then summed
together with offset. HF adjust and var gain are fed directly to the preamp from
the daculator (U904).
Preamp Control 4. U1403 and U1404 (sheet 7) are the serial in, parallel out shift
registers that load the preamp control bits. Serial data flows into U1403 pin 1
(from sheet 21, U1050, pin 27). The data is shifted into the registers by SCLK3
(U1403 and U1404, pin 8). SCLK3 comes from sheet 21, U1050, pin 12. Data
flows from the last bit of U1043 to the serial input pin of U1404 and then from
the last bit of U1404 back to sheet 21, U1050, pin 7 for diagnostic purposes.
There are three steps in the process of programming the preamps. First, 16 bits
are shifted into the two registers (U1403 and U1404) – only QA, QB, QC, QD,
and QE of each register will be used. The Ch1/Ch3 preamp strobe (sheet 3,
TDS 520B Mod CM Component Service Manual
1–7
Detailed Circuit Description
JP1400, pin 112 and sheet 5, JP1200, pin 112) is strobed to latch the gain and
bandwidth bits into Ch1 and Ch3. This strobe pin comes from sheet 21, U1050,
pin 17. Next, 16 more bits are shifted in and again only the 10 bits mentioned
above are used. However, this time, the Ch2/Ch4 preamp strobe (sheet 4,
JP1400, pin 212 and sheet 6, JP1200, pin 212) is strobed to latch the gain and
bandwidth bits into Ch2 and Ch4. Finally, 16 more data bits are shifted in. These
are left there to set the output controls of all four channels.
Preamp 4. The preamps amplify the input voltage. Input signals come from the
attenuator. The nominal gain of each preamp is 1.05 (at 50 mV per division); the
gain of the attenuator is 0.95 (in 1X attenuation). The combined gain from BNC
connector to A/D Converter D is 1.00.
Preamp 4 is an integrated circuit containing:
H Two four-pole bandwidth-limit filters: 20 MHz and 250 MHz. Inputs B0–B1
control the bandwidth of Preamp 4. See Table 1–2.
H Six gain settings of 1 mV, 2 mV, 5 mV, 10 mV, 20 mV, and 50 mV per
division (see Table 1–3). Inputs G0–G2 control the gain of Preamp 4.
H High-frequency adjust inputs.
H A variable gain control input which linearly adjusts the overall gain. The
gain is zero at –1 V and maximum at +1 V.
H Three separate differential outputs that can be turned on or off using the
output enable control signals (out1en, out2en, out3en). The inv controls are
left at 0.
T able 1–2: Bandwidth Limit Selection Bits(Cont.)
Bandwidth B1 B0
20 MHz 0 0
250 MHz 0 1
Maximum 1 X
T able 1–3: Gain Set Bits
Gain Setting G2 G1 G0
1 mV 0 0 0
2 mV 0 0 1
5 mV 0 1 0
10 mV 0 1 1
1–8
TDS 520B Mod CM Component Service Manual
T able 1–3: Gain Set Bits (Cont.)
Gain Setting G0G1G2
20 mV 1 0 X
50 mV 1 1 X
Detailed Circuit Description
Track/Hold A10
8
The track/hold IC (U1250) samples the differential analog signals coming from
the preamps before sending them to the A/D converters. The A/D clocks are also
provided by the track/hold. The track/hold IC also provides all channel switching
necessary to facilitate 2–way and 4–way interleaving. There are 8 control bits
that are serially shifted into U1251 and parallel fed to the track/hold. The data
line (SDATA, U1251 pin 1) comes from sheet 21, U1050, pin 27. The data is fed
back (SDIAG1, U1251, pin 13) to U1050, pin 5 for diagnostic purposes). The
data is clocked in by U1251, pin 8 (which comes from sheet 21, U1050 pin 10.)
The differential analog signals coming from the preamps are labelled
DISP1+/DISP1– thru DISP4+/DISP4–. The differential clocks going to the A/D
converters are labelled CLKAH/CLKAL thru CLKDH/CLKDI. The differential
analog sampled signals going to the A/D converters are labelled AP+/AP–
through DP+/DP–. Note, from the top level block diagram, that the signals going
from the preamps to the A/D converters get crossed (see Tables 1–4, 1–5, and
1–6 to verify this).
T able 1–4: Preamps to Track/Hold Input
Track/Hold
Preamps
Ch1 DISP1
Ch2 DISP2
Ch3 DISP4 Ch3 and Ch4 cross here
Ch4 DISP3
Input
Comments
T able 1–5: Track/Hold Outputs to A/D Input
Track/Hold
Outputs
AP SIGB AP and BP cross here
BP SIGA
CP SIGC CP and DP are inactive on
DP SIGD
A/D Input Comments
TDS 520B Mod CM Component Service Manual
the TDS 520B and
TDS 724A
1–9
Detailed Circuit Description
T able 1–6: Preamps to Track/Hold Input
Track/Hold
Clock
Outputs
CLKA CLKB
CLKB CLKA
CLKC CLKC CLKC and CLKD are inactive
CLKD CLKD
A/D Clock
Input
Comments
on the TDS 520B and
TDS 724A
In order to provide interleave capability, the Track/Hold must independently
adjust the delays of each of the sample clocks going to the A/D converters. These
are controlled by PHSA, PHSB, PHSC, and PHSD (pins 10, 111, 31, and 90
respectively of U1250) analog control voltages from the daculator (sheet 24,
U906). A three phase version of the 1GHz timebase clock is fed in through the
PHS1, PHS2, and PHS3 signals.
A/D Converters A10
1211109
NOTE. The TDS 520B and 724A only have A/D converts A and B. C and D are
not placed.
Since each A/D converter is similar, only the circuitry for A/D Converter D is
described. A/D Converter D (U700) converts the selected differential analog
input voltage to an 8-bit binary number. The analog input sensitivity is 2 mV per
digitizing level. Conversions occur at the 1 GHz clock rate (CLKD U700, pins
53 and 55). Even though conversions occur at this rate, data is output as two
differential 8-bit words (D0H/D0L–D7H/D7L and A0H/A0L–A7H/A7L) at a
500 MHz rate.
Pipes C and D (sheets 11 and 12) are not placed in the TDS 520B and TDS
724A.
Inputs. The A/D converter has one differential input (pins 60 and 62) fed from
the track/hold. Tables 1–4, 1–5, and 1–6 show which track/hold output connects
to which A/D converter. The 1 GHz differential input clocks from the track/hold
are fed into pins 53 and 55. Each side of the differential clock is 250 mV p–p
swing with the high level at 0 V.
Outputs. Outputs from the A/D Converter are differential, 500 mV digital swings
(peak to peak on each side.) The output resistance is 65 ohms. The two 8–bit 500
1–10
TDS 520B Mod CM Component Service Manual
Detailed Circuit Description
MS/s streams become valid on alternate edges of the clock cycle (D is valid on
the rising edge, A is valid on the falling edge.)
Control. The A/D converter has two DC analog controls: OFFSET, which sets the
A/D offset, and VREF, which adjusts the gain. These controls come from a
daculator IC (U906, sheet 24). The VREF control voltage is preconditioned by
U701 so that it ranges from 1.56 V to 3.44 V.
Sampling of the analog input voltage occurs on the positive going transition of
convert clock (CLK0, pins 53 and 55). Digitized value is available after the 11th
subsequent clock cycle.
DMUX & Acquisition
Memory A10
ADATA_D
DDATA_D
ADCLK_D
8
8
16151413
Level shift
Trigger
interface
NOTE. The TDS 520B and 724A only have pipes A and B placed. They do not use
C and D.
Since the circuitry for each demultiplexer and acquisition memory is similar,
only the circuitry for pipe D Acquisition Memory is described. The demultiplexer is the time base and memory control system for the output of an A/D
converter. Each demultiplexer has an A/D data input (Ch4D and Ch4A),
acquisition memory output, DSP bus interface, and a trigger interface (see
Figure 1–2).
Demultiplexer Level shiftDecimators
Counters
64
Acquisition
memory
Decode
TriStar
interface
Figure 1–2: Demultiplexer Block Diagram
TDS 520B Mod CM Component Service Manual
Formatter
1–11
Detailed Circuit Description
Demultiplexer D. Demultiplexer D has two operating modes. In acquire mode,
Demultiplexer D (U100) collects data from an A/D converter and writes the data
into Acquisition Memory D. In save mode, the DSP reads the acquired data from
Acquisition Memory D. The display system then processes and displays the data.
In acquire mode, Demultiplexer D (U100) gets its data (ADATA_DH0/ADATA_DL0 – ADATA_DH7/ADATA_DL7 and DDATA_DH0/DDATA_DL0 –
DDATA_DH7/DDATA_DL7) from A/D Converter D (U700) at a rate of two
new 8-bit samples every 2 ns. The input data sample is a 500 mV swing with
Von 4.2V. It latches the data on the falling edge of clock ADCLK_D and
converts it to CMOS levels. Data then passes to a demultiplexer at full speed, or
is decimated under program control.
The decimation mode determines the sample-rate. When the digital trigger is the
source of the trigger, the state of the decimators is latched at the trigger to assist
in point placement.
There are three decimation modes: normal, min/max, and hires:
H Normal (sub-sample) mode throws away samples between saved sample
points.
H Min/max mode saves the maximum and minimum samples over the
decimation interval.
H Hires mode gives extra resolution by averaging the samples, on a single-shot
basis, over the decimation interval.
An internal demultiplexer splits the two 8-bit data streams coming out of the
decimators into 16 8-bit data streams. The data streams are 2–way interleaved
resulting in a 64–bit data bus, with two memory chips on each byte. This results
in a 64-bit wide data word.
Demultiplexer D has three programmable counters that keep track of the number
of samples before the trigger, the number of samples after the trigger, and the
location in Acquisition Memory D where the trigger occurred. Before a trigger
occurs, the RUNM signal is asserted by the trigger logic (U1001, pin 146, sheet
20). After the trigger when the proper number of post–trigger samples have been
taken, RUNM is deasserted which stops the DMUX and causes it to interrupt the
processor.
During save mode, the DSP can access Acquisition Memory D. Memory mapped
I/O select MMIO accesses pin 74, the internal programming and status registers.
To further decode the MMIO select, the middle address bits are used as
sub-system selects.
1–12
Input MMIOA (U100, pin 73) acts as the sub-system selector for the memory
mapped I/O in the demultiplexers. To address the internal registers, DSP asserts
both MMIO and MMIOA.
TDS 520B Mod CM Component Service Manual
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