Tektronix ADA400A Service and user manual

Instruction Manual
ADA400A Differential Preamplifier
070-9164-01
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 the Safety Summary prior to performing service.
Copyright © T ektronix, Inc. 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. T ektronix, Inc., P.O. Box 500, Beaverton, OR 97077 TEKTRONIX and TEK are registered trademarks of T ektronix, Inc.

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

General Safety Summary iii. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Getting Started 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Product Description 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Accessories 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Installation 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Functional Check 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Operating Basics 7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Determining the Effective Volts/Division 10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Reference 11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Connecting the Inputs 11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Setting the Controls 15. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Tips for Reducing Signal Interference 19. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Specifications 21. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Nominal Characteristics 21. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
W arranted Characteristics 22. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
T ypical Characteristics 24. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Performance Verification 29. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Requirements for Performance 29. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Equipment Required 29. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Procedures 30. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Adjustment Procedures 37. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Requirements for Performance 37. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Equipment Required 37. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Procedure 38. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Maintenance 47. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Warranty Service 47. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Preparation 47. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Cleaning 48. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Replacement Procedures 48. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Replacement Parts 52. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Theory of Operation 52. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Troubleshooting 54. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Repackaging Instructions 54. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Replaceable Parts 55. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Parts Ordering Information 55. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Using the Replaceable Parts List 56. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Glossary 61. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Index 63. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ADA400A Differential Preamplifier
i
Contents

List of Figures

Figure 1: Configuration Jumper for Scale Factor Coding 3. . . . . . . . . . . . . . . . . .
Figure 2: Front Panel Controls 7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 3: Input Connectors and Fuses 8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 4: Output Connector 8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 5: Selecting the Input Impedance 13. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 6: Differential Rejection of Common-Mode Signal 14. . . . . . . . . . . . . . . . .
Figure 7: Eliminating Ground Loops in a Differential Setup 15. . . . . . . . . . . . . . .
Figure 8: Input and Offset Range for X 0.1 Gain 17. . . . . . . . . . . . . . . . . . . . . . . .
Figure 9: Input and Offset Range for X 1 Gain 17. . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 10: Input and Offset Range for X 10 Gain 17. . . . . . . . . . . . . . . . . . . . . . . .
Figure 11: Input and Offset Range for X 100 Gain 18. . . . . . . . . . . . . . . . . . . . . . .
Figure 12: Typical DC and AC Coupled CMRR in X0.1 Gain 26. . . . . . . . . . . . . .
Figure 13: Typical AC and DC Coupled CMRR in X1 Gain 27. . . . . . . . . . . . . . . .
Figure 14: Typical and Warranted CMRR in X10 Gain 27. . . . . . . . . . . . . . . . . . . .
Figure 15: T ypical and Warranted CMRR in X100 Gain 28. . . . . . . . . . . . . . . . . . .
Figure 16: Location of Adjustments Underneath Inner Shield 39. . . . . . . . . . . . . .
Figure 17: Replacing TEKPROBE Interface Pins 49. . . . . . . . . . . . . . . . . . . . . . . .
Figure 18: Replacing the TEKPROBE collar 49. . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 19: Input Connectors and Fuses 50. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 20: Potentiometer Connections 51. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 21: Diagram of the ADA400A Differential Preamplifier 52. . . . . . . . . . . . .
Figure 22: ADA400A Differential Preamplifier — Exploded View 59. . . . . . . . . .

List of Tables

Table 1: Gain settings 5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
T able 2: Controls, Connectors, and Indicators 9. . . . . . . . . . . . . . . . . . . . . . . . . .
T able 3: Effective Volts Per Division Settings 10. . . . . . . . . . . . . . . . . . . . . . . . . .
T able 4: Nominal Characteristics — Signal Acquisition System 21. . . . . . . . . . . .
T able 5: Warranted Characteristics — Signal Acquisition System 22. . . . . . . . . . .
T able 6: Warranted Characteristics — Environmental 23. . . . . . . . . . . . . . . . . . . .
T able 7: Typical Characteristics — Signal Acquisition System 24. . . . . . . . . . . . .
T able 8: Typical Characteristics — Mechanical Characteristics 26. . . . . . . . . . . . .
T able 9: Test Equipment 29. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
T able 10: Equipment Settings for Gain Checks 31. . . . . . . . . . . . . . . . . . . . . . . . .
T able 11: Equipment Settings for X100, 100 kHz CMRR Checks 33. . . . . . . . . . .
T able 12: Equipment Settings for X100, 10 kHz CMRR Checks 34. . . . . . . . . . . .
T able 13: Equipment Settings for X100, 100 Hz CMRR Checks 35. . . . . . . . . . . .
T able 14: Equipment Settings for X10, 100 kHz CMRR Checks 35. . . . . . . . . . . .
T able 15: Equipment Settings for X10, 10 kHz CMRR Checks 36. . . . . . . . . . . . .
T able 16: Equipment Settings for X10, 100 Hz CMRR Checks 36. . . . . . . . . . . . .
T able 17: Equipment Settings for Gain Adjustments 40. . . . . . . . . . . . . . . . . . . . .
T able 18: Equipment Settings for Offset Adjustments 41. . . . . . . . . . . . . . . . . . . .
T able 19: Equipment Settings for Attenuator Balance Adjustments 42. . . . . . . . .
T able 20: Equipment Settings for CMRR Adjustments 43. . . . . . . . . . . . . . . . . . .
T able 21: Equipment Settings for LF Adjustments 45. . . . . . . . . . . . . . . . . . . . . . .
T able 22: Second Equipment Settings for LF Adjustments 45. . . . . . . . . . . . . . . .
T able 23: Electrical Faults 54. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ADA400A Differential Preamplifier
ii

General Safety Summary

Review the following safety precautions to avoid injury and prevent damage to this product or any products connected to it.
Only qualified personnel should perform service procedures.

Injury Precautions

Avoid Electric Overload
Ground the Product
Do Not Operate Without
Covers
Do Not Operate in
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 oscilloscope 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 electric shock, do not operate this product in wet or damp conditions.
Wet/Damp Conditions
Do Not Operate in
Explosive Atmosphere
To avoid injury or fire hazard, do not operate this product in an explosive atmosphere.

Product Damage Precautions

Do Not Operate With
Suspected Failures
Do Not Immerse in Liquids
ADA400A Differential Preamplifier
If you suspect there is damage to this product, have it inspected by qualified service personnel.
Clean the instrument using only a damp cloth. Refer to cleaning instructions.
iii
General Safety Summary

Safety Terms and Symbols

Terms in This Manual
Terms on the Product
These terms may appear in this manual:
WARNING. Warning statements identify conditions or practices that could result in injury or loss of life.
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.
Symbols on the Product
iv
The following symbols may appear on the product:
DANGER
High Voltage
Protective Ground
(Earth) T erminal
ATTENTION
Refer to
Manual
ADA400A Differential Preamplifier
Double
Insulated

Preface

This manual contains both user and service information for the ADA400A Differential Preamplifier. The following is a brief overview of what each section of the manual contains.
H Getting Started includes a description of the product features and a list of
standard and optional accessories. This section also describes how to supply power to the preamplifier and how to connect the preamplifier to an oscilloscope.
H Operating Basics contains a graphical overview and a brief description of
each control and connector of the ADA400A Differential Preamplifier.
H The Reference section describes how to connect the ADA400A Differential
Preamplifier to small signals and make the proper settings.
H Specifications lists the electrical and mechanical characteristics of the
ADA400A Differential Preamplifier.
H Performance Verification contains procedures for verifying the warranted
characteristics of the ADA400A Differential Preamplifier.
H The sections behind the warning page contain service information for the
ADA400A Differential Preamplifier: Adjustment Procedures, Maintenance and Replaceable Parts.
ADA400A Differential Preamplifier
v
Preface

Contacting Tektronix

Phone 1-800-833-9200*
Address Tektronix, Inc.
Department or name (if known) 14200 SW Karl Braun Drive P.O. Box 500 Beaverton, OR 97077 USA
Web site www.tektronix.com
Sales support 1-800-833-9200, select option 1*
Service support 1-800-833-9200, select option 2*
Technical support Email: techsupport@tektronix.com
1-800-833-9200, select option 3* 1-503-627-2400
6:00 a.m. – 5:00 p.m. Pacific time
* This phone number is toll free in North America. After office hours, please leave a
voice mail message. Outside North America, contact a Tektronix sales office or distributor; see the Tektronix web site for a list of offices.
ADA400A Differential Preamplifier
vi

Getting Started

Product Description

Getting Started includes a description of the product features and a list of standard and optional accessories. This section also describes how to supply power to the preamplifier and how to connect the preamplifier to an oscilloscope.
The ADA400A Differential Preamplifier allows direct oscilloscope measure­ments of very low amplitude voltages and signals that do not have a ground reference. These measurements are typical in setups that depend on transducers or other sensitive devices to supply the electrical signal.
Highlights of the ADA400A Differential Preamplifier are as follows: H Selectable gains of X100, X10, X1, and X0.1 provide wide range of
sensitivity.
H Common-mode rejection of greater than or equal to 100,000 to 1 in the
frequency range of DC to 10 kHz removes unwanted common mode electrical noise from sensitive pickups.

Accessories

H Bandwidth of greater than or equal to 1 MHz amplifies signals with fast
transients. Selectable bandwidth limits of 100 Hz, 3 kHz, 100 kHz reject normal-mode noise.
H Input impedance of 1 MW in all settings and selectable impedance of
infinite W (u10 impedance prevents loading down signals with high source impedance.
H Adjustable differential offset allows the user to null out transducer bridge
bias, galvanic potentials from the test setup, or other DC voltages.
H Special circuitry greatly reduces the annoying DC drift commonly found in
older types of differential preamplifiers.
H TEKPROBE Interface provides power input and signal output connections.
Standard accessories for the ADA400A Differential Preamplifier include the following items:
H This instruction manual H Two spare input fuses
12
W) in X100 and X10 gain settings. The high input
ADA400A Differential Preamplifier
1
Getting Started

Installation

Recommended accessories for the ADA400A Differential Preamplifier include the following items:
H P6101B 1X Passive Probe H 1103 Probe Power Supply for oscilloscopes that do not have the TEK-
PROBE Interface.
Before you connect the output of the ADA400A Differential Preamplifier, determine whether or not your oscilloscope has the TEKPROBE interface. The interface provides connections for power, signal, and scale factor coding for compatible probes and accessories.
Oscilloscopes with the
TEKPROBE Interface
The polarized output connector of ADA400A Differential Preamplifier connects to any oscilloscope with the TEKPROBE interface.
NOTE. To avoid misleading scale factor readouts of the ADA400A Differential Preamplifier, the oscilloscope must be compatible with the scale factor coding; otherwise, you must remove the preamplifier housing and disconnect the internal line that carries the scale factor coding.
Compatible Oscilloscopes. Most oscilloscopes with the TEKPROBE interface, except the 11000 Series models, are compatible with the scale factor coding of the ADA400A Differential Preamplifier. The factory configures the internal jumper to connect the scale factor coding. See Figure 1.
Perform the Functional Check on page 4, steps 1–6, and verify that the oscilloscope volt/division readings match the manual for all gain settings in step
6. If the readings are not correct for any scale setting, the oscilloscope is not compatible with the scale factor coding of the ADA400A Differential Preamplifi­er. In this case, use the procedure that follows to disable the scale factor coding.
1. Remove the top housing of the preamplifier by following the procedures on
page 50.
2. Identify the jumper on the data line (See Figure 1) and position the jumper to
disable the scale factor coding.
3. Replace the top housing on the preamplifier box.
ADA400A Differential Preamplifier
2
Figure 1: Configuration Jumper for Scale Factor Coding
Getting Started
Enabled Disabled
Oscilloscopes without the
TEKPROBE Interface
Because the line that carries the scale factor coding is disabled, see the chart on page 10 to correctly interpret the volts/division setting of the oscilloscope.
Connecting the TEKPROBE Output. To engage the TEKPROBE output, align the fin on the output head counterclockwise with the clearance on the oscilloscope connector. Push the connector in and and lock the fin clockwise.
Use the 1103 TEKPROBE Power Supply to connect the ADA400A Differential Preamplifier to any oscilloscope that does not provide TEKPROBE power. The 1103 TEKPROBE Power Supply has connections for two probe channels.
NOTE. Use the offset controls of the ADA400A Differential Preamplifier to adjust the offset level. The offset controls on the 1103 TEKPROBE Power Supply do not operate with the ADA400A Differential Preamplifier.
Because the 1103 TEKPROBE Power Supply does not connect the line that carries the scale factor coding, see the chart on page 10 to correctly interpret the volts/division setting of the oscilloscope.
For more information about using the 1103 TEKPROBE Power Supply, refer to the instruction manual that comes with the power supply.
ADA400A Differential Preamplifier
3
Getting Started
Check the Oscilloscope
Input Impedance and
Coupling

Functional Check

Always set the input impedance of the oscilloscope to 1 MW and the input coupling of the oscilloscope to DC. Setting the impedance to 50 W loads (reduces) the amplitude of the output signal from the ADA400A Differential Preamplifier. AC coupling on the oscilloscope interferes with the signal output. Use the input coupling switch on the preamplifier to select other types of signal coupling.
The following procedure checks the output level of the ADA400A Differential Preamplifier and the functionality of the offset controls with no signal applied.
1. Without any connection on the input of the oscilloscope, power on the
oscilloscope and make the following control settings: Volts/Division 100 mV
Time/Division 100 ms Input Coupling DC Input Impedance 1 MW
2. Adjust the oscilloscope to display a flat signal trace at center screen.
3. Connect the output of the ADA400A Differential Preamplifier (or 1103
TEKPROBE Power Supply) to the input connector of the oscilloscope.
4. With no input signal or voltage connected, make the following control
settings on the ADA400A Differential Preamplifier: AC GND DC GND (both inputs)
GAIN 0.1 OFFSET OFF UPPER BANDWIDTH FULL (1 MHz)
5. Check that the trace on the oscilloscope centers around zero volts and the
OVERRANGE indicator does not light.
6. Set the GAIN switch to each of the higher gain settings and check that the
trace on the oscilloscope is adjustable to center screen. Make sure the volts/division reading on the scope matches the readings below in table 1. If the readings do not match, the oscilloscope is not compatible with the scale factor coding of the ADA400A Differential Preamplifier. See page 2. If the scale factor coding is disabled, see table 3 on page 10 for proper readings.
ADA400A Differential Preamplifier
4
Getting Started
T able 1: Gain settings
Gain setting Oscilloscope reading
0.1 1.00 V 1 100 mV 10 10.0 mV 100 1.00 mV
7. With the GAIN switch on the highest setting, set the ON OFF switch for the OFFSET controls to ON.
8. Adjust the COARSE and FINE controls to bring the trace to center screen.
9. Set each input separately to AC, DC, and back to GND and check that the
offset controls still bring the trace to center screen for each setting.
10. Return the GAIN setting to .1 and the input coupling switches to GND.
The ADA400A Differential Preamplifier is now ready to use. For a complete performance verification procedure, refer to page 29.
ADA400A Differential Preamplifier
5
Getting Started
ADA400A Differential Preamplifier
6

Operating Basics

Vertical Gain Control
Operating Basics contains a graphical overview and a brief description of each control and connector of the ADA400A Differential Preamplifier. See Figures 2 through 4 and Table 2.
W
W1
Input Coupling
Overrange Indicator
Upper Bandwidth
Selector
} }
Vertical Offset Controls
Figure 2: Front Panel Controls
ADA400A Differential Preamplifier
7
Operating Basics
+ Input Fuse – Input Fuse– Input BNC
+ Input BNC
Connector
Figure 3: Input Connectors and Fuses
Connector
Signal Output
BNC
TEKPROBE Interface Pins
Figure 4: Output Connector
ADA400A Differential Preamplifier
8
T able 2: Controls, Connectors, and Indicators
Feature Description
Input BNCs. The BNC connectors provide the differential input connections to the
preamplifier. These connectors accept coaxial cables, 1X probes, adapters, or other input leads that terminate with male BNC connectors. Before connecting the inputs, see page 11.
NOTE. Avoid using attenuating probes. The slightest difference in attenuation match
+ Input BNC
Connector
– Input BNC
Connector
greatly lowers the common-mode rejection ratio.
Input Fuses. The input fuses and internal circuitry protect the input circuits from excessive surge currents. To replace the fuses, see page 50.
Operating Basics
+ Input
Fuse
} }
– Input
Fuse
W
W1
Selectable Impedance. Internal jumpers select infinite impedance for measuring signals with high source impedance. To select the input impedance, see page 12.
Input Coupling Switches. Use the input coupling switches to select the proper mode for coupling the input signals to the internal inputs of the preamplifier.
The AC position couples the input signal through a capacitor and blocks any DC and AC components of the signal from 0 to 2 Hz.
GND decouples the signal from the input and couples the internal input of the preamplifier to ground. This position also precharges the coupling capacitor to the DC level of the input signal (see page 16).
The DC position couples both AC and DC components of the input signal. Overrange Indicator. The OVERRANGE indicator lights red when the signal input
exceeds the selected range of the amplifier. If the indicator is on, the output signal is not a true representation of the input signal(s). See page 16.
Gain Selector. The gain selectors set the gain of the preamplifier to X0.1, X1, X10, or X100. If the oscilloscope does not display the correct volts per division for each gain setting, refer to Table 3 on page 10.
Offset Controls. The ON/OFF switch activates the offset controls. The COARSE and FINE controls provide a maximum of 40 volts offset in the X0.1 and X1 gain settings and a maximum of 1 volt offset in X10 and X100 gain settings. See page 16.
ADA400A Differential Preamplifier
9
Operating Basics
T able 2: Controls, Connectors, and Indicators (Cont.)
Feature Description
Upper Bandwidth Selector. The Upper Bandwidth Selector reduces electrical
interference by limiting the frequency response of the amplifier to FULL (1 MHz), 100 kHz, 3 kHz, or 100 Hz.
Output Connector. The output connector contains connections for the TEKPROBE interface and signal output.

Determining the Effective Volts/Division

If your oscilloscope cannot read the scale factor information, see Table 3 to determine the effective volts/division setting. The effective volts per division is the volts per division setting of the oscilloscope divided by the gain setting of the ADA400A Differential Preamplifier. For example, if the volts/division setting on the oscilloscope is 500 mV/division and the gain setting is 10, the effective volts/division is 500 divided by 10 or 50 mV.
T able 3: Effective Volts Per Division Settings
Scope Volts/Div
1 10 1 100 m 10 m 500 m 5 500 m 50 m 5 m 200 m 2 200 m 20 m 2 m 100 m 1 100 m 10 m 1 m 50 m 500 m 50 m 5 m 500 m 20 m 200 m 20 m 2 m 200 m 10 m 100 m 10 m 1 m 100 m
Gain = .1
Effective Volts Per Division
Gain = 1 Gain = 10 Gain = 100
10
5 m 50 m 5 m 500 m 50 m 2 m 20 m 2 m 200 m 20 m 1 m 10 m 1 m 100 m 10 m
ADA400A Differential Preamplifier

Reference

Connecting the Inputs

The Reference section describes how to connect the inputs of the ADA400A Differential Preamplifier and make the proper control settings. To achieve the best performance it is important to make the proper signal and ground connec­tions, set the controls to optimize the performance of the preamplifier, and reduce unwanted electrical interference.
Making the proper input connections is crucial to maintaining the fidelity of the signal as well as eliminating unwanted noise. The characteristics of the signal source and the type of measurement you wish to make, determine the type of input leads you should use and the way you should connect the inputs.
WARNING. Do not attach the ADA400A Differential Preamplifier to human subjects for any testing or bio-monitoring. The ADA400A Differential Preampli­fier is not safety certified for direct connection to humans.
Input Devices
The ADA400A Differential Preamplifier is able to amplify extremely small signals that may or may not have a ground reference. Often the signals originate from low-level, low-frequency transducers, and other similar sources of small differential or floating voltages.
The inputs of the ADA400A Differential Preamplifier connect easily to devices or leads that terminate with male BNC connectors. There are numerous adapters readily available that can adapt other types of wire, cables, or plugs to a BNC connector.
NOTE. Avoid using attenuating probes. The slightest difference in attenuation match greatly lowers the common-mode rejection ratio.
ADA400A Differential Preamplifier
11
Reference
Using the Proper Input
Leads
Input Voltages
Input Protection
To reduce unwanted electrical interference on the input leads, use shielded coaxial cable or the recommended 1X probes to connect signals to the preampli­fier inputs. The shielding in these types of leads intercepts and shunts electrical noise to ground.
When you must use any length of unshielded wire, twist the wires together and connect the wires differentially. Twisting the wires together helps to introduce any electrical interference as common-mode noise that the differential preampli­fier cancels out with a differential setup on the inputs.
For other tips on reducing signal interference, refer to page 19.
Because the ADA400A Differential Preamplifier is designed to amplify small DC and AC voltages, do not connect voltages that exceed the input rating.
CAUTION. To avoid damaging the inputs of the ADA400A Differential Preampli­fier, do not apply more than 40 volts (DC + peak AC) between any one input and ground or 80 volts (DC + peak AC) differential between the inputs.
To prevent damage to the input circuitry from the misapplication of large voltages, a fuse on each input opens if the input current exceeds 62 mA ( To replace or check these fuses, refer to the procedure on page 50.
1
/16 A).
12
Input Impedance
Each input connector of the ADA400A Differential Preamplifier has a character­istic input impedance of 1 MW to ground in parallel with approximately 55 pF. For low source impedances, this 1 MW is more than adequate to prevent the inputs from loading the signal source.
If impedance of the signal source approaches 1 MW, the impedance of the inputs begin to load the signal source and reduce the amplitude. In effect, the extremely low current of the signal source is not able to develop a voltage across the 1 MW resistance and there is no signal to amplify. In this case you may want to select the infinite W position.
Infinite W. To measure signals from high impedance sources, you can internally disconnect the 1 MW resistance of the ADA400A Differential Preamplifier. and select the infinite W position. This position prevents the preamplifier from loading a high impedance signal source.
Observe the following operating limitations when you select the infinite W position:
H Select either the X100 or the X10 gain position. Operation in the 0.1X and
1X gain results in gain errors.
ADA400A Differential Preamplifier
Reference
H Ensure that the source has some impedance to ground. The internal input
amplifier requires some input bias current to operate. Typically this amount of input bias current is less than 25 pA.
H Select the DC coupling position when operating the preamplifier. The AC
coupling position blocks the bias current that the preamplifier input requires to operate.
H Take steps to reduce interference from other sources (see page 19). Because
the input impedance is essentially infinite you may notice an increased susceptibility to noise and DC drift.
Selecting the Infinite W Position. To select the infinite impedance, remove the knobs and top housing of the preamplifier. Do not remove the inner shield. With a pair of needle-nose pliers or tweezers, move the jumpers from the 1 MW to the infinite W position as Figure 5 illustrates.
Input Configurations
Input+ Input
Infinite W
1 MW
Figure 5: Selecting the Input Impedance
There are two basic types of input configurations on the ADA400A Differential Preamplifier: single-ended or differential. Whether one or the other of these configurations is appropriate depends on the type of signal and the electrical environment of the test setup.
Single-Ended. To monitor a ground-referenced signal you only need to make a single input connection. All the controls on the preamplifier still operate. The only difference is that the preamplifier cannot cancel out common mode noise without using the other input connection. When making single-ended measure­ments, set the coupling for the unused input to GND.
ADA400A Differential Preamplifier
13
Reference
Single-ended measurements, however, often yield unsatisfactory information because of interference resulting from ground-loop currents between the oscilloscope and the device under test. In other cases, it is desirable to eliminate a common-mode DC voltage without using a DC blocking capacitor or the AC coupling capacitor of the preamplifier. These capacitors limit low-frequency response. Connecting the signals differentially virtually eliminates these effects.
Differential. Figure 6 shows two signals connected to the ADA400A Differential Preamplifier. One signal is connected to the + input and the other is connected to the – input. Because the preamplifier inverts the signal at the – input, the preamplifier amplifies only differential voltages between the inputs and rejects (cancels) voltages that are common to both inputs. The oscilloscope displays the waveform of the differential signal only.
NOTE. To avoid creating a fictitious differential offset, set both AC GND DC coupling switches to the same AC or DC switch position.
+
Differential
Amplifier
Figure 6: Differential Rejection of Common-Mode Signal
To avoid ground loops in a differential setup it is important to leave the grounds of the shielded coax disconnected and to route the chassis ground to the oscilloscope ground using a separate ground lead. Figure 7 on page 15 illustrates this type of connection.
14
ADA400A Differential Preamplifier
Reference
Oscilloscope Input
Impedance and Coupling

Setting the Controls

+
Differential
Amplifier
Circuit
Under Test
Common Ground
Oscilloscope
Input
Figure 7: Eliminating Ground Loops in a Differential Setup
Always set the input impedance of the oscilloscope to 1 MW and the input coupling of the oscilloscope to DC. Setting the impedance to 50 W loads (reduces) the amplitude of the output signal from the ADA400A Differential Preamplifier. AC coupling on the oscilloscope interferes with the signal output. Use the input coupling switch on the preamplifier to select other types of signal coupling.
Input Coupling
The controls of the ADA400A Differential Preamplifier determine signal coupling, amplification, DC offset, and the bandwidth limit.
The type of input coupling you select depends on whether or not you want to pass or block the DC component of the input signal.
AC Coupling. Setting the coupling switch to AC places a capacitor in the signal path and blocks DC to about 2 Hz signals. Select the AC position to block DC components on the signal input and couple AC signals higher than approximate­ly 2 Hz. This setup is useful when the test setup has a DC bias which drifts.
NOTE. To prevent the circuit under test from receiving the effects of charging and discharging the AC coupling capacitor, refer to the procedure for Precharging
the Signal Input in the section that follows.
ADA400A Differential Preamplifier
15
Reference
GND Coupling. The GND position decouples the signal from the input and couples the internal input of the preamplifier to ground. This position also precharges the AC coupling capacitor to the DC level of the signal. (See the following section, Precharging the Signal Input.)
DC Coupling. The DC position couples all signal components, AC and DC, to the preamplifier. (You can adjust the offset controls to null out DC biases.)
Precharging the Signal
Input
Gain, Input Range, and
Offset Range
Follow the procedure below when coupling AC signals that have a high DC voltage level or when probing between signals that differ greatly in DC levels. This procedure becomes especially useful when you disable the 1 MW input resistance and it takes a long time to charge the input capacitors back to the bias voltage.
1. Set the input coupling switch to GND before connecting the input to a signal
source.
2. Connect the preamplifier input to the signal source.
3. Wait two seconds for the input coupling capacitor to charge to the DC level
of the signal source.
4. Set the input coupling switch to AC. Position the AC signal within the
graticule area on the oscilloscope display.
The gain selector sets amplification factor of the preamplifier to X0.1, X1, X10, or X100. Each gain setting has a characteristic differential or single-ended range, a common-mode (dynamic) range, and variable offset range. To prevent the signal from distorting or “clipping” (see Figure 10) you must use the appropriate gain setting and offset.
The amount of differential, common-mode, and offset range depends on the gain setting. Figures 8 through 11 beginning on page 17 show the common-mode, differential, and offset range for each gain setting of the preamplifier.
16
The OVERRANGE indicator lights when the input signal is outside the differential input range for a particular gain setting. This light indicates that the output signal is distorted or “clipped” and the oscilloscope display may not be accurate. Try a lower gain setting or check the position of the offset controls if the OVERRANGE indicator is on.
ADA400A Differential Preamplifier
80 40
30 20 10
10203040
80
Maximum
Single-Ended
Input
Common-Mode
and Offset
Range
Figure 8: Input and Offset Range for X 0.1 Gain
40 30 20 10
10203040
Maximum Differential or Single Ended Input
Common-Mode
Range and Offset
Range
Reference
Maximum
Differential Input
Figure 9: Input and Offset Range for X 1 Gain
(Clipped
+10 V
Maximum
Differential and
Single-Ended Input
+1 V
1 V
10 V
Waveform)
Common-Mode
Range
Offset Range
Figure 10: Input and Offset Range for X 10 Gain
ADA400A Differential Preamplifier
17
Reference
+10V
Adjusting the Offset
Controls
+1V
+100mV
100mV
1V
10V
Maximum
Differential and
Single-Ended Input
Offset Range
Common Mode
Range
Figure 11: Input and Offset Range for X 100 Gain
Setups that have a large DC offset, but must measure small changes in DC voltage or signal voltage below 2 Hz, require that you to adjust the offset controls of the preamplifier. Typical setups include those with transducers or setups that measure galvanic potentials.
To compensate for a DC offset, perform the following procedure:
1. Set the input coupling to GND on both inputs of the preamplifier and switch offset controls to OFF.
18
Limiting Bandwidth
2. Preset the GAIN switch of the preamplifier and the volts/division switch of the oscilloscope to the appropriate settings based on the amount of offset you expect to measure. See Figures 8 through 11. (Select a lower gain setting if you are unsure of the amount of the offset.)
3. Center the oscilloscope display using the vertical position control on the oscilloscope.
4. Set the offset controls ON and center the display with the COARSE and FINE offset controls.
5. Set the input coupling to DC on the signal input(s) and, if necessary,
measure the amount of DC offset.
6. Center the display using the COARSE and FINE controls and change the volts/division setting on the oscilloscope to better display the signal.
The ADA400A Differential Preamplifier has a selector for limiting the upper bandwidth. Limiting the bandwidth is desirable in setups where electrical interference from higher frequency sources is a problem. The ADA400A
ADA400A Differential Preamplifier
Differential Preamplifier allows you to select upper bandwidth limits of FULL (1 MHz), 100 kHz, 3 kHz and 100 Hz.

Tips for Reducing Signal Interference

Disruptive electrical interference or “noise” from sources near the test setup can affect measurements. The effects become even more apparent when measuring low-amplitude voltages.
The electric-power system, for example, generates a line frequency of 50 or 60 Hz and can couple electrical noise from other devices. Power switches or switching devices generate power line spikes. Unshielded or poorly grounded electric motors can generate disruptive transients. Power lines and transformers create magnetic fields that can induce a disruptive voltage in wires or input leads that are not properly twisted together.
Devices such as digital or microprocessor based systems can radiate signals that sensitive electronic detectors or amplifiers can receive and amplify. Switch-mode power supplies generate interference in the range of 20 to 100 kHz. Sources of interference can include florescent lights, laser printers, monitors, CRTs, even radio transmissions.
Reference
Signal and Ground
Connections
Proper setup of the ADA400A Differential Preamplifier minimizes or eliminates signal interference in most cases. There are three important strategies to reducing signal interference:
1. Use the proper signal and ground connections for the particular application.
2. Limit the bandwidth of the test setup.
3. Isolate or eliminate sources of signal interference.
The techniques for proper signal and ground connections involve limiting noise to the input:
H Minimize length of input leads. H Select input leads that have the same length and type of construction. H Use shielded coaxial cable or twisted-pair leads on the inputs. H Connect shield or ground leads close to signal source. H Restrict movement of input leads. H Eliminate ground loops. H Reject common-mode noise by operating in differential mode.
ADA400A Differential Preamplifier
19
Reference
Bandwidth Limiting
Isolating or Eliminating
Sources of Interference
Limiting the bandwidth is a useful technique for keeping unwanted high frequency noise from interfering with the display of lower frequency signals. The ADA400A Differential Preamplifier allows you to limit the upper bandwidth to 100 Hz, 3 kHz, 100 MHz, and FULL (1 MHz).
Some pieces of electronic or electrical equipment can generate enormous amounts of electrical noise. One solution is to isolate or eliminate the noise that these devices emit:
H Move sources of noise away from test setup or isolate test setup. H Shield test setup. H Make sure all electronic equipment that is connected to the AC power line is
properly grounded through the power cord.
20
ADA400A Differential Preamplifier

Specifications

This section describes three classes of characteristics for the ADA400A Differential Preamplifier: nominal, warranted, and typical.

Nominal Characteristics

Nominal traits are described using simple statements of fact such as “Differen- tial, + and ‘–’” for the characteristic Input Configuration, rather than in terms of limits that are performance requirements.
T able 4: Nominal Characteristics — Signal Acquisition System
Name Description
Input Configuration Differential, + and ‘–’ Input Coupling DC, AC, or GND
Ground coupling connects a ground reference to the input of the attenuator or differential amplifier and allows the AC coupling capacitor to charge up to the
input voltage through a large resistance. Gain Settings 0.1, 1, 10, 100 Analog Bandwidth Selections 100 Hz, 3 kHz, 100 kHz, and FULL (1 MHz) Offset Ranges Gain Setting Offset Range
0.1 ± 40 V
1 ± 40 V
10 ± 1 V
100 ± 1 V
ADA400A Differential Preamplifier
21
Specifications

Warranted Characteristics

Warranted characteristics are described in terms of quantifiable performance limits which are warranted.
NOTE. In these tables, those warranted characteristics that are checked in the procedure Performance Verification appear in boldface type under the column
Name.
The performance limits in this specification are valid with these conditions:
H This instrument must have been calibrated/adjusted at an ambient tempera-
H The instrument must be in an environment with temperature, altitude,
H The instrument must have had a warm-up period of at least 20 minutes.
ture of 22 ± 5_ C.
humidity, and vibration within the operating limits described in these specifications.
H The instrument must be used with an oscilloscope that is compatible with the
scale factor coding of the ADA400A Differential Preamplifier. See page 2.
T able 5: Warranted Characteristics — Signal Acquisition System
Name Description Input Resistance, DC Coupled 1 MW ±2% DC Gain Accuracy ±2%
Maximum Input Voltage 30 VAC
input; derate at 20 dB/decade above 1 MHz.
Differential Signal Range (DC OFFSET not used) Gain Setting Differential Input Signal Range
0.1 ±80 V 1 ±10 V 10 ±1 V 100 ±100 mV
Common Mode Signal Range Gain Setting Common Mode Input Signal Range
0.1 ±40 V 1 ±40 V 10 ±10 V 100 ±10 V
, 42 V (DC + peak AC), between signal and common of the same
RMS
22
ADA400A Differential Preamplifier
T able 5: Warranted Characteristics — Signal Acquisition System (Cont.)
Name Description
Specifications
Common Mode Rejection Ratio
(See Figures 14 to 15 on page 27.)
1
The limits given are for the ambient temperature of 22 ±5_ C
Frequency Gain Setting
100 Hz 10 85 dB
10 kHz 85 dB
100 kHz 60 dB
100 Hz 100 90 dB
10 kHz 90 dB
100 kHz 60 dB
T able 6: Warranted Characteristics — Environmental
Name Description
Atmospherics Temperature
Operating: 0_ C to +50_ C Non-operating: –55_ C to +75_ C
Relative Humidity (tested to the following limits)
Operating: 90–95% RH, +30_ C to +50_ C
CMRR1 (DC coupled)
Non-operating: 90–95% RH, +30_ C to +60_ C
Dynamics Random Vibration
Operating: 2.66 g rms overall, 3 axis, 20 min/axis (60 min total) Non-operating: 3.48 g rms overall, 3 axis, 20 min/axis (60 min total)
Mechanical Shock
Half Sine, 500 g’s 3 axis, 3 drops each axis, 1 ms duration, 18 drops total
ADA400A Differential Preamplifier
23
Specifications
T able 6: Warranted Characteristics — Environmental (Cont.)
Name Description
Electromagnetic Compatibility (EMC) Emissions:
Meets or exceeds the requirements of the following standards:
EN 55022 Class B limits for radiated emissions when operated as a system with a TDS460 series oscilloscope (FCC 47 CFR, Part 15, Subpart B for Class A equipment.)
ADA400A Settings: Gain=100; Offset=off; DC coupled; Filter=1 MHz TDS 460 Settings: 500 ns/div; 5 mV/div; DC coupled
Immunity: Radio Frequency Electromagnetic Field
less than ±2 divisions of leakage signal when the instrument is subjected to a 3 V/M electromagnetic field over the frequency range of 27 MHz to 500 MHz.
Electrostatic Discharge (ESD)
Up to 8 kV with no change to control settings of impairment of normal operation, and up to 15 kV with no loss of stored data or damage that prevents recovery of normal operation by the user.

Typical Characteristics

Typical characteristics are described in terms of typical or average performance. Typical characteristics are not warranted.
T able 7: Typical Characteristics — Signal Acquisition System
Name Description
Input Capacitance 55 pF ± 20% Analog Bandwidth Selection Accuracy ± 12% for 100 Hz, 3 kHz, 100 kHz selections
1 MHz for the FULL (1 MHz) selection Linearity ± 0.01% of linear dynamic range Lower Frequency Limit, AC Coupled 2 Hz (lower –3 dB frequency) Harmonic Distortion 0.002% measured using 3 V Recovery Time ≤ 1.5 ms to recover to within 0.5% of zero level after over driving the amplifier
by ± 150%
output at 100 Hz and 1 kHz
RMS
24
ADA400A Differential Preamplifier
T able 7: Typical Characteristics — Signal Acquisition System (Cont.)
Name Description
Specifications
Zero Offset (Offset control off)
DC Offset Drift with Temperature Gain Setting Offset On Offset Off
Input Current Less than 25 pA at an ambient temperature of 22 ± 5_ C Random Noise RMS Noise
Bandwidth Selection Gain of 0.1 Gain of 1 Gain of 10 Gain of 100
1 MHz 5 mV 3 mV ≤50 mV ≤30 mV 100 kHz 4 mV 1 mV ≤40 mV ≤10 mV 3 kHz 4 mV 1 mV ≤40 mV ≤10 mV 100 Hz 4 mV 1 mV ≤40 mV ≤10 mV
Common Mode Rejection Ratio (See Figures 12 to 15 on pages 26 to 28)
Gain Setting
0.1 ±50 mV 1 ±5 mV 10 ±500 mV 100 ±50 mV
0.1 0.750 mV/_ C 0.250 mV/_ C 1 0.300 mV/_ C 0.200 mV/_ C 10 10 mV/_ C 5 mV/_ C 100 5 mV/_ C 3 mV/_ C
Frequency Gain Setting
100 Hz 0.1 60 dB 45 dB 10 kHz 52 dB 50 dB 100 kHz 50 dB 50 dB 100 Hz 1 75 dB 50 dB 10 kHz 60 dB 55 dB 100 kHz 52 dB 52 dB 100 Hz 10 100 dB 75 dB 10 kHz 100 dB 95 dB 100 kHz 90 dB 90 dB 100 Hz 100 100 dB 80 dB 10 kHz 100 dB 100 dB 100 kHz 90 dB 90 dB
Zero Offset Referred to the Input of the Amplifier
CMRR (DC coupled)
CMRR (AC coupled)
ADA400A Differential Preamplifier
25
Specifications
T able 8: Typical Characteristics — Mechanical Characteristics
Name Description
Weight Shipping: 1.78 kg (3.92 lbs) including accessories
Net Weight: 1.14 kg (2.51 lbs) Overall Dimensions Height: 36 mm (1.42 in)
Width: 1 12 mm (4.41 in)
Depth: 203 mm (8.00 in) Cable Length 2 m (78.7 in)
Gain – 0.1
110 100
90 80 70
dB
DC Typical
60 50
AC Typical
40 30 20 10
0
10 100 1 k 10 k
Frequency (Hz)
Figure 12: Typical DC and AC Coupled CMRR in X0.1 Gain
100 k 1 M
26
ADA400A Differential Preamplifier
Gain – 1.0
110 100
90 80
DC Typical
70
dB
60
AC Typical
50 40 30 20 10
0
10 100 1 k 10 k
Frequency (Hz)
Specifications
100 k 1 M
Figure 13: Typical AC and DC Coupled CMRR in X1 Gain
Gain – 10.0
110
DC Typical
100
90
DC Warranted
80
AC Typical
70
dB
60 50 40 30 20 10
0
10 100 1 k 10 k
Frequency (Hz)
100 k 1 M
Figure 14: Typical and Warranted CMRR in X10 Gain
ADA400A Differential Preamplifier
27
Specifications
Gain – 100.0
110
DC Typical
100
DC Warranted
90 80
AC Typical
70
dB
60 50 40 30 20 10
0
10 100 1 k 10 k
100 k 1 M
Frequency (Hz)
Figure 15: Typical and Warranted CMRR in X100 Gain
28
ADA400A Differential Preamplifier

Performance Verification

This section contains procedures for checking that the ADA400A Differential Preamplifier meets warranted specifications.

Requirements for Performance

The performance limits of this procedure are valid with the following conditions: H The ADA400A Differential Preamplifier is in an environment that is within
the operating limits of temperature, altitude, humidity, and vibration described in Specifications.
H The data line jumper located inside the ADA400A Differential Preamplifier.
is properly configured depending on the type of oscilloscope you connect to the output. See the Installation section on page 2.
H The ADA400A Differential Preamplifier has a period of at least a 20 minutes
to warm up prior to verification.

Equipment Required

Table 9 lists the equipment required to verify and adjust the ADA400A Differential Preamplifier. The Adjustment Procedures section begins on page 37.
T able 9: Test Equipment
Item Number and Description
1. Digitizing Oscilloscope Bandwidth: > 5 MHz
2. Sine Wave Generator Frequency Range: 1 Hz to
3. Digital Multimeter Resolution: 3.5 digits
Minimum Requirements Example Purpose
Sensitivity: 1 mV/div Auto Measurement: Frequency, Amplitude Input Impedance: 1 MW Must have TekProbe Level 2 Meet functional check with scale factor coding (see page
2).
5 MHz
Accuracy: 0.5% Resistance Range: 200 W to 10 MW
–– Supply power to and display
output of ADA400A
SG5030 CMRR checks and adjustments
DM2510 Input resistance check
ADA400A Differential Preamplifier
29
Performance Verification
T able 9: Test Equipment (Cont.)
Item Number and Description
PurposeExampleMinimum Requirements
4. Calibration Generator Calibrated Amplitude:
Period: 1 ms Amplitude: 50 mVp-p to 20 V p-p into 1 MW Aberrations: 2% p-p Accuracy: 0.5%
Fastrise: 500 ns 1 Vp-p into 50 W
5. BNC Adapters BNC Female to Dual Banana Tektronix part number
6. Dual Input Connector Dual Input Cable BNC Tektronix part number
7. 50 W Terminators (2) 50 W, 2W, BNC Tektronix part number
8. 10X Attenuators (2) 10:1 Attenuator, 50 W, BNC Tektronix part number
9. Coaxial Cables (2) 50 W, 36 in. L, BNC male both
ends
10. Adjustment Tool, Probe Plastic Insulated Tektronix part number
CG5011 Gain check and adjustment.
103–0090–00
067–0525–02
011–0049–01
011–0059–02 Tektronix part number
012–1341–00
003–0675–01
LF Compensation adjustments
Signal connection
Signal connection
Signal connection
Signal attenuation
Signal connection
Adjustments (Adjustment Procedure only)

Procedures

30
Before beginning the procedures in this section, connect the output of the ADA400A Differential Preamplifier to the oscilloscope, turn the oscilloscope on, and let the ADA400A warm up for 20 minutes.
NOTE. Before performing these procedures, make sure your oscilloscope can display the proper scale factor. If you are using an oscilloscope that is not compatible with the scale factor coding of the ADA400A Differential Preamplifi­er to perform these procedures, see page 2 to properly configure the scale factor coding.
To convert the volts/division settings for oscilloscopes that cannot read the scale factor from the ADA400A, multiply the volts/div setting in the procedure by the gain setting of the ADA400A.
ADA400A Differential Preamplifier
Performance Verification
Input Resistance
Equipment Required
One digitizing oscilloscope (item 1) to supply power to the ADA400A One digital multimeter (item 3) One BNC female to dual banana connector (item 5) One coaxial cable (item 9)
1. Set digital multimeter to measure resistance.
2. Connect banana-to-BNC adapter to digital multimeter.
NOTE. To avoid an erroneous resistance measurement, make sure the 1 MW input resistance jumpers are installed.
3. Set ADA400A + input to DC.
4. Connect coaxial cable from + input of ADA400A to the BNC-to-banana
adapter on the multimeter.
5. Check input resistance = 1 MW ± 2% (980 kW to 1.02 MW).
6. Remove coaxial cable from ADA400A + input and connect it to the
‘–’ input.
Gain
7. Set the ADA400A ‘–’ input to DC.
8. Check input resistance = 1 MW ± 2% (980 kW to 1.02 MW).
Equipment Required
One digitizing oscilloscope (item 1) One dual input coupler (item 6) One calibration generator (item 4) One coaxial cable (item 9)
1. Connect the ADA400A to Ch1 of the oscilloscope and make the equipment
settings according to Table 10.
T able 10: Equipment Settings for Gain Checks
ADA400A Control Setting
+ Input DC – Input Gnd Gain 100 Upper Bandwidth 100 kHz
ADA400A Differential Preamplifier
31
Performance Verification
T able 10: Equipment Settings for Gain Checks (Cont.)
ADA400A Control Setting
Offset Off
Oscilloscope Control Setting
Channel Selection Ch1 Vertical input impedance 1 MW Vertical gain 10 mV/div Time base 200 ms/div Vertical Coupling DC Vertical Position 0 V (mid-scale) Trigger Edge Trigger position 50% Trigger source Ch4 Acquisition mode Hi Res Auto Measurement Amplitude Bandwidth Full
Calibration Generator Control Setting
Output 50 mV, 1 kHz
2. Connect a dual input connector to inputs of ADA400A.
3. Connect a coaxial cable from calibration generator output to dual input
connector.
4. Adjust vertical position knob on the oscilloscope to center square wave on
screen.
5. Check DC gain accuracy is ± 2% (49 to 51 mV). (Use amplitude measure-
ment function.)
6. Set ADA400A gain setting to 10.
7. Set calibration generator to 0.5 V amplitude.
8. Adjust vertical position knob on oscilloscope to center square wave on
screen.
9. Check DC gain accuracy is ± 2% (490 mV to 510 mV).
10. Set ADA400A gain setting to 1.
32
11. Set calibration generator to 5 V amplitude.
ADA400A Differential Preamplifier
Performance Verification
12. Adjust vertical position knob on oscilloscope to center square wave on
screen.
13. Check DC gain accuracy is ± 2% (4.9 V to 5.1 V).
14. Set ADA400A gain setting to 0.1.
15. Set calibration generator to 20 V amplitude.
16. Adjust vertical position knob on oscilloscope to center square wave on
screen.
17. Check DC gain accuracy is ± 2% (19.6 V to 20.4 V).
18. Disconnect setup from the inputs of the ADA400A.
CMRR
Equipment Required
One digitizing oscilloscope (item 1) One sine wave generator (item 2) One dual input coupler (item 6) One 50 W terminator (item 7) Two 10X attenuators (item 8) Two coaxial cables (item 9)
1. Connect the ADA400A to Ch1 of the oscilloscope and make the equipment
settings according to Table 11.
T able 11: Equipment Settings for X100, 100 kHz CMRR Checks
ADA400A Setting
+ Input DC – Input Gnd Gain 100 Upper Bandwidth FULL (1 MHz) Offset Off
Oscilloscope Setting
Vertical gain 2 mV/div Time base 5 ms/div Acquisition mode Average Number of waveforms to average 20 Trigger source Ch4
ADA400A Differential Preamplifier
33
Performance Verification
T able 11: Equipment Settings for X100, 100 kHz CMRR Checks (Cont.)
Sine Wave Generator Setting
Output 100 kHz, 1 Vp-p into 50 W
2. Connect a coaxial cable from sine wave generator trigger output to Ch4 of
the oscilloscope.
3. Connect dual input connector to inputs of ADA400A.
4. Connect 50 W terminator to dual input connector.
5. Connect two 10X attenuators to 50 W terminator.
6. Connect a coaxial cable from sine wave generator output to 10X attenuators.
7. Adjust trigger level for a steady display.
8. Adjust the amplitude of the sine wave generator for 5 divisions on screen.
9. Remove the two 10X attenuators and connect the cable directly to the 50 W
terminator.
10. Set ADA400A ‘–’ input to DC.
11. Set oscilloscope to 1 mV/div.
12. Measure signal is 1 division (1 mV, 60 dB).
13. Modify the equipment settings according to Table 12.
T able 12: Equipment Settings for X100, 10 kHz CMRR Checks
ADA400A Setting
Upper Bandwidth 100 kHz
Oscilloscope Setting
Vertical gain 2 mV/div Time base 50 ms/div
Sine Wave Generator Setting
Output 10 kHz
34
14. Set ‘–’ input to GND.
15. Do steps 5 to 10.
16. Set oscilloscope to 10 mV/div. Measure trace is t 3.2 divisions wide (32 mV,
90 dB).
ADA400A Differential Preamplifier
Performance Verification
17. Modify the equipment settings according to Table 13.
T able 13: Equipment Settings for X100, 100 Hz CMRR Checks
ADA400A Setting
Upper Bandwidth 3 kHz
Oscilloscope Setting
Vertical gain 2 mV/div Time base 5 ms/div
Sine Wave Generator Setting
Output 100 Hz
18. Set ‘–’ input to GND.
19. Do steps 5 to 10.
20. Set oscilloscope to 10 mV/div. Measure trace is t 3.2 divisions wide (32 mV,
90 dB).
21. Modify the equipment settings according to Table 14.
T able 14: Equipment Settings for X10, 100 kHz CMRR Checks
ADA400A Setting
Gain 10 Upper Bandwidth 1 MHz
Oscilloscope Setting
Vertical gain 20 mV/div Time base 5 ms/div
Sine Wave Generator Setting
Output 100 kHz
22. Set ‘–’ input to GND.
23. Do steps 5 to 10 but with only one 10X attenuator.
24. Set oscilloscope to 1 mV/div. Measure trace is t 1 division wide (1 mV,
25. Modify the equipment settings according to Table 15.
ADA400A Differential Preamplifier
60 dB).
35
Performance Verification
T able 15: Equipment Settings for X10, 10 kHz CMRR Checks
ADA400A Setting
Upper Bandwidth 100 kHz
Oscilloscope Setting
Vertical gain 20 mV/div Time base 50 ms/div
Sine Wave Generator Setting
Output 10 kHz
26. Set ‘–’ input to GND.
27. Do steps 5 to 10 but with only one 10X attenuator.
28. Set oscilloscope to 100 mV/div. Measure trace is t 0.56 division wide
(56 mV, 85 dB).
29. Modify the equipment settings according to Table 16.
T able 16: Equipment Settings for X10, 100 Hz CMRR Checks
ADA400A Setting
Upper Bandwidth 3 kHz
Oscilloscope Setting
Vertical gain 20 mV/div Time base 5 ms/div
Sine Wave Generator Setting
Output 100 Hz
30. Set ‘–’ input to GND.
31. Do steps 5 to 10 but with only one 10X attenuator.
32. Set oscilloscope to 100 mV/div. Measure trace is t 0.56 division wide
(56 mV, 85 dB).
33. Disconnect setup.
36
This completes the performance verification procedure.
ADA400A Differential Preamplifier
WARNING
The following servicing instructions are for use only by qualified personnel. To avoid injury, do not perform any servicing other than that stated in the operating instructions unless you are qualified to do so. Refer to all safety summaries before performing any service.

Adjustment Procedures

Use the procedures in this section to return the ADA400A Differential Preampli­fier to conformance with the Warranted Characteristics listed in the Specifica- tions section on page 21.
Before performing any procedures in this section, please read the sections entitled Requirements for Performance and Equipment Required.

Requirements for Performance

Before performing these procedures, please address the following requirements:
H You must be a trained service technician to perform this procedure. H You must adjust the ADA400A Differential Preamplifier in an environment
in which temperature, altitude, humidity, and vibration are within the operating limits described in Specifications.
H You must calibrate the ADA400A Differential Preamplifier at the center
temperature range of 22 ± 5_ C.

Equipment Required

H You must warm up the ADA400A Differential Preamplifier for at least 20
minutes prior to adjustment.
For a complete list of equipment required to perform the procedures in this section, see the Equipment Required section under Performance Verification on page 29.
ADA400A Differential Preamplifier
37
Adjustment Procedures

Procedure

Before you begin these procedures, remove the top housing using the procedure on page 50. Leave the inner shield in place. See Figure 16 for a diagram of the adjustment locations.
NOTE. To avoid contaminating the sensitive areas of the circuit board, do not remove inner shield or touch the circuit board. Access all adjustments through holes of inner shield
Connect the output of theADA400A Differential Preamplifier to the oscillo­scope, turn the oscilloscope on, and let the ADA400A warm up for 20 minutes.
NOTE. Before performing these procedures, make sure your oscilloscope can display the proper scale factor. If you are using an oscilloscope that is not compatible with the scale factor coding of the ADA400A Differential Preamplifi­er to perform these procedures, see page 2 to properly configure the scale factor coding.
To convert the volts/division settings for oscilloscopes that cannot read the scale factor from the ADA400A, multiply the volts/div setting in the procedure by the gain setting of the ADA400A.
38
ADA400A Differential Preamplifier
Adjustment Procedures
CV14
(LF Compensation)
*CV13
R18
(HF CMRR)
*CV17
RV106
(10X Gain)
RV32
(Offset Zero)
CV6 (LF Compensation)
*CV12
*CV18
RV17 (LF CMRR)
CV4 (HF)
RV62 (100X Gain)
RV33 (Offset Balance)
Figure 16: Location of Adjustments Underneath Inner Shield
ADA400A Differential Preamplifier
*Factory adjust only
39
Adjustment Procedures
Gain Adjustments
Equipment Required
One digitizing oscilloscope (item 1) One dual input coupler (item 6) One calibration generator (item 4) One coaxial cable (item 9) One adjustment tool (item 10)
1. Connect the ADA400A to Channel 1 and make the equipment settings
according to Table 17.
T able 17: Equipment Settings for Gain Adjustments
ADA400A Setting
+ Input DC – Input Gnd Gain 100 Upper Bandwidth 100 kHz Offset Off
Oscilloscope Setting
Channel Selection Ch1 Vertical input impedance 1 MW Vertical gain 10 mV/div Time base 200 ms/div Coupling DC Vertical Position 0 V (mid-scale) Trigger Edge Trigger position 50% Trigger source Ch4 Acquisition mode Hi Res Auto Measurement Amplitude Bandwidth Full
Calibration Generator Setting
Output 50 mV calibrated, 1 kHz
2. Connect a dual input connector to inputs of ADA400A.
3. Connect a coaxial cable from the output of the calibration generator to the
dual input connector.
40
ADA400A Differential Preamplifier
Adjustment Procedures
4. Adjust vertical position knob on the oscilloscope to center square wave on
screen.
5. Adjust RV62 for 5.0 divisions on screen (50 mV).
6. Set ADA400A gain setting to 10.
7. Set calibration generator to 0.5 V amplitude.
8. Adjust the vertical position knob on the oscilloscope to center square wave
on screen.
9. Adjust RV106 to 5.0 divisions.
Zero Offset Adjustments
Equipment Required
One digitizing oscilloscope (item 1)
1. Connect the ADA400A to Channel 1 and make the equipment settings
according to Table 18.
T able 18: Equipment Settings for Offset Adjustments
ADA400A Setting
+ Input Gnd – Input Gnd Gain 10 Upper Bandwidth 100 Hz Offset Off (remains off through out the test)
Oscilloscope Control Setting
Channel Selection Ch1 Vertical input impedance 1 MW Vertical gain 500 mV/div Time base 5 ms/div Vertical Coupling DC Vertical Position 0 V (mid-scale) Trigger mode Auto Acquisition mode Hi Res Bandwidth Full
2. Check to make sure oscilloscope is at position 0 and vertical offset 0.
ADA400A Differential Preamplifier
41
Adjustment Procedures
3. Switch the gain setting between 10 and 100 while adjusting RV33 for
minimum shift in the oscilloscope trace.
a. Make note of trace position at gain setting of 10. b. Switch gain setting to 100. c. Adjust trace to where it was at the gain setting of 10. d. Repeat steps a to c until there is a minimum amount of shift.
4. Adjust RV32 to center trace on screen.
5. Switch the gain setting from 0.1, 1, 10 and 100 and verify that trace does not
shift more than one division from center.
6. Disconnect setup.
LF CMRR Adjustments
Equipment Required
One digitizing oscilloscope (item 1) One sine wave generator (item 2) One dual input coupler (item 6) One 50 W terminator (item 7) Two coaxial cables (item 9) One adjustment tool (item 10)
1. Connect the ADA400A to Channel 1 and make the equipment settings
according to Table 19.
T able 19: Equipment Settings for Attenuator Balance Adjustments
ADA400A Setting
+ Input DC – Input Gnd Gain 1 Upper Bandwidth 100 Hz
Oscilloscope Setting
42
Vertical gain 1 V/div Time base 20 ms/div Trigger Source Ch4
Sine Wave Generator Setting
Output 10 Hz
ADA400A Differential Preamplifier
Adjustment Procedures
2. Connect dual input connector to inputs of ADA400A.
3. Connect 50 W terminator to dual input connector.
4. Connect a coaxial cable from sine wave generator output to 50 W terminator.
5. Connect another coaxial cable from trigger output of sine wave generator to
Ch4 of oscilloscope.
6. Adjust sine wave generator attenuator variable knob for 5 divisions (5 V) on
screen.
7. Set ADA400A ‘–’ input to DC.
8. Set oscilloscope volts/div to 1 mV.
9. Adjust RV17 for minimum signal amplitude.
10. Disconnect setup.
CMRR Adjustments
Equipment Required
One digitizing oscilloscope (item 1) One sine wave generator (item 2) One dual input coupler (item 6) One 50 W terminator (item 7) Two 10X attenuators (item 8) Two coaxial cables (item 9) One adjustment tool (item 10)
1. Connect the ADA400A to Channel 1 and make the equipment settings
according to Table 20.
T able 20: Equipment Settings for CMRR Adjustments
ADA400A Setting
+ Input DC – Input Gnd Gain 100 Upper Bandwidth FULL (1 MHz)
Oscilloscope Setting
Vertical gain, Ch 1 2 mV/div Time base 5.0 ms/div Acquisition mode Average
ADA400A Differential Preamplifier
43
Adjustment Procedures
T able 20: Equipment Settings for CMRR Adjustments (Cont.)
Oscilloscope Setting
Number of waveforms to average 20 Trigger source Ch4
Sine Wave Generator Setting
Output 100 kHz, 1 Vp-p into 50 W
2. Connect a coaxial cable from trigger output of sine wave generator to Ch4 of
oscilloscope.
3. Connect dual input connector to inputs of ADA400A.
4. Connect 50 W terminator to dual input connector.
5. Connect two 10X attenuators to 50 W terminator.
6. Connect a coaxial cable from sine wave generator output to 10X attenuators.
LF Compensation
Adjustments
7. Adjust trigger level for a steady display.
8. Adjust amplitude for 5 divisions (10 mV) on screen.
9. Remove the two 10X attenuators and connect the cable directly to the 50 W
terminator.
10. Set ADA400A ‘–’ input to DC.
11. Set oscilloscope to 2 mV/div.
12. Adjust CV4 and R18 for minimum signal amplitude ( 1 mV).
13. Disconnect setup.
Equipment Required
One digitizing oscilloscope (item 1) One calibration generator (item 4) One dual input coupler (item 6) One 50 W terminator (item 7) Two coaxial cables (item 9) One adjustment tool (item 10)
44
1. Connect the ADA400A to Channel 1 and make the equipment settings
according to Table 21.
ADA400A Differential Preamplifier
T able 21: Equipment Settings for LF Adjustments
ADA400A Setting
+ Input DC – Input Gnd Gain 1 Upper Bandwidth Full (1 MHz)
Oscilloscope Setting
Vertical gain, Ch1 200 mV/div Time base 20 ms/div
Calibration Generator Setting
Output Mode Fast Rise, 10 kHz
2. Connect dual input connector to ADA400A input.
Adjustment Procedures
3. Connect 50 W terminator to dual input connector.
4. Connect a coaxial cable to calibration generator fast rise output to 50 W
terminator.
5. Connect a coaxial cable from trigger out of calibration generator to Ch4 of
oscilloscope.
6. Adjust amplitude for 5 divisions on screen.
7. Adjust CV6 for flat response.
8. Make the second equipment settings according to Table 22.
T able 22: Second Equipment Settings for LF Adjustments
ADA400A Setting
+ Input DC – Input DC
Oscilloscope Setting
Vertical gain 5 mV/div Time base 20 ms/div
9. Adjust CV14 for minimum trace.
10. Disconnect setup.
This completes the ADA400A adjustment procedures.
ADA400A Differential Preamplifier
45
Adjustment Procedures
46
ADA400A Differential Preamplifier

Maintenance

Warranty Service

This section details the maintenance and replacement procedures for the ADA400A Differential Preamplifier.
Tektronix warrants this product for three years from date of purchase. (A complete warranty statement appears at the front of this manual.) Tektronix provides warranty service at most Tektronix service locations worldwide. The Tektronix product catalog lists all service locations worldwide.
Should the ADA400A Differential Preamplifier require replacement under terms of the warranty, return the preamplifier to a Tektronix service center. Include the following information: name of purchaser, return address, name and phone number of a person that Tektronix may contact, date of purchase, and a description of the defect.
In the U.S., call 1-800-TEK WIDE (1-800-835-9433) for further assistance.

Preparation

Before Servicing
Preventing ESD
This manual provides information for limited servicing of the ADA400A Differential Preamplifier
NOTE. Only qualified service personnel should attempt any internal repair or maintenance of the ADA400A Differential Preamplifier.
Before servicing the ADA400A Differential Preamplifier, please read the General Safety Summary starting on page iii.
The ADA400A Differential Preamplifier contains internal components that are susceptible to damage from electrostatic discharge (ESD).
ADA400A Differential Preamplifier
47
Maintenance

Cleaning

CAUTION. To prevent damaging internal components by means of electrostatic discharge (ESD), perform all service at a static-free work station and wear a grounded anti-static wrist strap.
Do not slide the internal module over any surface. Place internal module in static-free bag for transportation away from work station.
To prevent damage to the ADA400A Differential Preamplifier, avoid using chemicals that contain benzine, benzene, toluene, xylene, acetone, or similar solvents.
Do not immerse the ADA400A Differential Preamplifier or use abrasive cleaners.
Dirt on external surfaces may be removed with a soft cloth dampened with a mild detergent and water solution, or isopropyl alcohol.
NOTE. Certain areas of the circuit board are sensitive to surface contamination. Avoid touching the surfaces of the circuit board. Handle the circuit board by the edges. If the circuit board is contaminated, wash the board with Isopropyl Alcohol and rinse with warm deionized water.

Replacement Procedures

Refer to the procedures in this section before replacing any part on the ADA400A Differential Preamplifier. For a list of all customer replaceable parts, see the Replaceable Parts section that begins on page 55 and the exploded view on page 59.
Replacing TEKPROBE
Interface Pins
Periodically check to see that each of the interface pins move freely and fully extends out of the interface. If any pin fails to move freely and fully extend, it should be replaced.
To remove a TEKPROBE interface pin, firmly grasp the pointed tip with pliers and pull the pin out of the connector. See Figure 17.
No tools are required to install a replacement pin. Insert a new pin into the connector socket as far as possible using finger pressure. If necessary, seat the pin into the connector by pressing the tip gently but firmly against a hard surface, such as a wood block or table top.
48
ADA400A Differential Preamplifier
Figure 17: Replacing TEKPROBE Interface Pins
Maintenance
Replacing the TEKPROBE
Interface Collar
To remove the TEKPROBE interface collar, firmly grasp the body of the output head with one hand, and the TEKPROBE interface collar with the other hand. Firmly pull the interface collar off.
To replace the collar, first note the pin configuration in the interface collar. The group of three pins fit through the smaller of the two holes in the interface collar. Align the tab to the slot and gently press the two pieces together. See Figure 18.
Once installed, the TEKPROBE collar should rotate freely to lock and unlock.
Tab
Slot
Figure 18: Replacing the TEKPROBE collar
ADA400A Differential Preamplifier
49
Maintenance
Replacing the Input Fuses
To remove and replace an input fuse, insert a flat-blade screwdriver into the slot on the fuse cap, press in and turn counter clockwise to remove the fuse.
CAUTION. To properly protect the inputs of the ADA400A Differential Preamplifi­er, replace fuses with the type specified in the Replaceable Parts section.
Insert the replacement fuse into the cap on the fuse holder, insert, and use the flat-blade screwdriver to press in and lock the fuse cap counterclockwise.
+ Input Fuse – Input Fuse
Figure 19: Input Connectors and Fuses
Accessing Internal
Components
Replacing the
Potentiometers
To access internal components of the ADA400A Differential Preamplifier, refer to the exploded view, Figure 22, on page 59 and perform the following proce­dure:
1. Using a 1/16-inch Allen wrench, loosen the set screws on the COARSE and
FINE controls and remove the knobs.
2. Remove the four screws that hold the top housing, separate the top housing
from the bottom housing and set the top housing to one side.
STOP. If you intend to electrically adjust the ADA400A or move a jumper, do not proceed further. The adjustments and jumpers are accessible through holes in the circuit board shield. Proceed further only if you intend to replace parts under the shield.
3. Following the static precautions presented at the beginning of this section,
remove the screws on the top of the shield and carefully lay the shield over to the side without straining the wires of the potentiometers.
After performing the procedure to access the internal components of the ADA400A Differential Preamplifier, replace one of the potentiometers as follows:
50
ADA400A Differential Preamplifier
Maintenance
1. Unsolder the wires from the potentiometer.
2. Remove the nut on the shaft of the potentiometer and replace the potentiom-
eter with the new part. Replace and tighten the nut and washer on the shaft.
3. Resolder the wires as Figure 20 illustrates.
Replacing the Cable
Assembly
(Fine)
311–2533–00
Brown
Orange
Red
Orange
(Coarse)
311–2158–02
Brown
Red
Figure 20: Potentiometer Connections
After performing the procedure to access the internal components of the ADA400A Differential Preamplifier, replace the cable assembly as follows:
1. Remove the remaining two screws that hold the circuit board to the bottom
NOTE. To prevent contaminating sensitive areas of the circuit board, handle the circuit board by the edges only.
2. Unsolder the four colored wires from the top of the circuit board and the
3. Note the color-code information on the circuit board. Replace the cable
4. Place the circuit board and cable strain relief in the bottom housing and
ADA400A Differential Preamplifier
housing.
three ground prongs from the bottom of the circuit board.
assembly and solder the new wires.
reinstall hardware.
51
Maintenance

Replacement Parts

Theory of Operation

Refer to the Replaceable Parts section beginning on page 55 for a list of customer replacement parts.
Figure 21 illustrates the functional blocks of circuitry from left to right in the order of input to output. The darker boxes in the illustration designate front panel controls and lines with arrows indicate the functional blocks that the controls affect.
Input
ADA400A Differential Preamplifier
AC-GND-DC
+
Input Coupling/
Input Protection
1 M / 1 W
Select
High-Z
Attenuator
(1/1, 1/100)
Input Coupling/
Input Protection
AC-GND-DC
High-Impedance
Amplifier
+
Gain = X10
Gain .1, 1, 10, 100
DC
Offset
+
On/Off,
Coarse, Fine
Low-Z Attenuator (1/1, 1/10)
100 Hz, 3 kHz, 100 kHz 1 MHz
Scale Factor
Coding
Overrange
Detect
Output Amplifier
Low-Pass
Filter
Gain = X10
Upper Bandwidth Select
TEKPROBE
Interface
50 W
Output Cable
Oscilloscope
Signal Out
+15V –15V
+5V
Data
Ground
Figure 21: Diagram of the ADA400A Differential Preamplifier
52
ADA400A Differential Preamplifier
Maintenance
Input Protection and
Coupling
Input Impedance
Attenuation and
Amplification
Any signals on the inputs of the ADA400A Differential Preamplifier must pass through the input protection and coupling circuits.
Input Protection. The input protection circuit shunts excessively high-voltage signals to ground and blows the protective fuse if the current exceeds 1/16 am­pere for any length of time.
Input Coupling. The coupling switch for a particular input selects one of the following connections to the input of the preamplifier: AC, GND (ground), or DC. For more information on these switch positions, see page 15.
Internal jumpers connect an input impedance of 1 MW in parallel with 55 pF. With the jumpers disconnected the input impedance is virtually infinite (10 For more information about these jumpers, see page 12.
The gain switch sets the gain of the preamplifier by selecting the amount of attenuation at two different points in the circuitry: 1/1 or 1/100 attenuation in the high-impedance attenuator and 1/1 or 1/10 attenuation in the low-impedance attenuator. The lowest gain setting, for example, selects the highest total amount of attenuation.
12
W).
DC Offset
Low-Pass Filter
Overrange Detect
Scale-Factor Coding
TEKPROBE Interface
The offset controls adjust the DC component of the input signal. To keep the signal from distorting, the signal must be within the dynamic range of the amplifier. For more information on the dynamic range characteristic, refer to the notes on page 16.
The Upper Bandwidth Control selects different RC networks in the low-pass filter. The bandwidth settings are 100 Hz, 3 kHz, 100 kHz, and 1 MHz.
Should the input signal exceed the dynamic range of the output amplifier, the overrange detection circuit activates the indicator on the front panel.
The gain switch also selects a resistance that appears on the data pin. If the host oscilloscope is properly equipped (see Installation on page 2), this resistance determines the vertical scale factor on the oscilloscope display.
The TEKPROBE interface provides power, signal, and data connections between the ADA400A Differential Preamplifier and the oscilloscope.
ADA400A Differential Preamplifier
53
Maintenance

Troubleshooting

Table 23 lists symptoms of electrical faults, possible causes, and corrective actions.
T able 23: Electrical Faults
Symptom Possible Cause Corrective Action(s)
No power Damage to TEKPROBE interface connec-
tions. Check interface pins and cable assembly wires for damage.
No output signal on connector end of cable assembly or output too high or low
Intermittent or difficult positioning Defective position controls Replace position control(s) No signal output to cable assembly
interface power is present and fuses are not blown
Blown input fuse Damage to output cable
Faulty module Send unit to service center for exchange or
Replace interface pin(s) Replace or repair cable assembly
Check and replace fuse(s) Repair or replace cable assembly
replacement.

Repackaging Instructions

If the original packaging is unfit for use or not available, use the following packaging guidelines:
1. Use a corrugated cardboard shipping carton having inside dimensions at least
one inch greater than the probe dimensions. The box should have a carton test strength of at least 200 pounds.
2. Put the probe into a plastic bag or wrap to protect it from dampness.
3. Place the probe into the box and stabilize it with light packing material.
54
4. Seal the carton with shipping tape.
ADA400A Differential Preamplifier

Replaceable Parts

This section contains a list of the replaceable modules for the ADA400A Differential Preamplifier. Use this list to identify and order replacement parts.

Parts Ordering Information

Replacement parts are available through your local Tektronix field office or representative.
Changes to Tektronix instruments are sometimes made to accommodate improved components as they become available and to give you the benefit of the latest circuit improvements. Therefore, when ordering parts, it is important to include the following information in your order.
H Part number H Instrument type or model number H Instrument serial number H Instrument modification number, if applicable
Module Servicing
If you order a part that has been replaced with a different or improved part, your local Tektronix field office or representative will contact you concerning any change in part number.
Change information, if any, is located at the rear of this manual.
Modules can be serviced by selecting one of the following options. Contact your local Tektronix service center or representative for repair assistance.
Module Exchange. In some cases you may exchange your module for a reman­ufactured module. These modules cost significantly less than new modules and meet the same factory specifications. For more information about the module exchange program, call 1-800-TEK-WIDE, extension 6630.
New Modules. You may purchase replacement modules in the same way as other replacement parts.
ADA400A Differential Preamplifier
55
Replaceable Parts

Using the Replaceable Parts List

This section contains a list of the mechanical and/or electrical components that are replaceable for the ADA400A Differential Preamplifier. Use this list to identify and order replacement parts. The following table describes each column in the parts list.
Parts List Column Descriptions
Column Column Name Description
1 Figure & Index Number Items in this section are referenced by figure and index numbers to the exploded view
illustrations that follow. 2 Tektronix Part Number Use this part number when ordering replacement parts from Tektronix. 3 and 4 Serial Number Column three indicates the serial number at which the part was first effective. Column four
indicates the serial number at which the part was discontinued. No entries indicates the part is
good for all serial numbers. 5 Qty This indicates the quantity of parts used. 6 Name & Description An item name is separated from the description by a colon (:). Because of space limitations, an
item name may sometimes appear as incomplete. Use the U.S. Federal Catalog handbook
H6-1 for further item name identification. 7 Mfr. Code This indicates the code of the actual manufacturer of the part. 8 Mfr. Part Number This indicates the actual manufacturers or vendors part number.
Abbreviations
Mfr. Code to Manufacturer
Cross Index
Abbreviations conform to American National Standard ANSI Y1.1–1972.
The table titled Manufacturers Cross Index shows codes, names, and addresses of manufacturers or vendors of components listed in the parts list.
56
ADA400A Differential Preamplifier
Replaceable Parts
Manufacturers Cross Index
Mfr. Code
0JR05 TRIQUEST CORP 3000 LEWIS AND CLARK HWY VANCOUVER WA 98661–2999 0KB01 STAUFFER SUPPLY 810 SE SHERMAN PORTLAND OR 97214 18359 PYLON CO INC 51 NEWCOMB ST ATTLEBORO MA 02703–1403 22526 BERG ELECTRONICS INC (DUPONT) 857 OLD TRAIL RD ETTERS PA 17319 32997 BOURNS INC
61935 SCHURTER INC 1016 CLEGG COURT PETALUMA CA 94952–1152 71400 BUSSMANN
73743 FISCHER SPECIAL MFG CO 111 INDUSTRIAL RD COLD SPRING KY 41076–9749 78189 ILLINOIS TOOL WORKS INC
80009 TEKTRONIX INC 14150 SW KARL BRAUN DR
93907 TEXTRON INC
Manufacturer Address City, State, Zip Code
TRIMPOT DIV
DIV OF COOPER INDUSTRIES INC
SHAKEPROOF DIV
CAMCAR DIV
1200 COLUMBIA AVE RIVERSIDE CA 92507–2114
114 OLD STATE RD PO BOX 14460
ST CHARLES ROAD ELGIN IL 60120
PO BOX 500 600 18TH AVE ROCKFORD IL 61108–5181
ST LOUIS MO 63178
BEAVERT ON OR 97077–0001
ADA400A Differential Preamplifier
57
Replaceable Parts
Replaceable Parts List
Fig. & Index Number
221 380109800 1 HOUSING:TOP & BOTTOM,STEELZINC PLATE 80009 380109800
2 334890000 1 MARKER,IDENT:INSTRUMENT LABEL 80009 3348900003 366186103 2 KNOB:GREY,0.252 ID X 0.706 OD X0.612 H,
4211054100 4 SCREW,MACHINE:632 X 0.25,FLH,100 DEG,STL,CD PL,
5 220049500 2 NUT,PLAIN,HEX:0.375–32 X 0.438 HEX,BRS,CD PL 73743 ORDER BY DESC6 210001200 2 WASHER,LOCK:0.384 ID,INTL,0.022 THK,STL 78189 1220020005417 337403700 1 SHIELD:0.040 STEEL,ZINC PLATE,7.5X 5.0 80009 3374037008311215802 1 RES,VAR,WW:PNL,5K OHM,5%,1W 32997 84A1CB24J139 –––––––––– 1 CIRCUIT BD ASSY:MAIN
10 159002400 2 FUSE,CARTRIDGE:3AG,0.062A,250V,0.3 SEC 71400 AGC 1/1611 200226400 2 CAP,FUSEHOLDER:3AG FUSES 61935 FEK 031 166612 131099300 3 CONN,BOX:SHUNT ,;FEMALE,STR,1 X 2,0.1 CTR,
13 220049700 2 NUT,PLAIN,HEX:0.528 X 0.562 HEX,BRS CD PL 73743 ORDER BY DESC14 210098600 2 WASHER,FLAT:0.5 ID X 0.672 OD X 0.035,STL CD PL 80009 21009860015 2110711–00 4 SCR,ASSEM WSHR:6–32 X 0.250,PNH,STL,CDPL,
16 210103900 2 WASHER,LOCK:0.521 ID,INT ,0.025 THK,SST 0KB01 1224020054117 348018700 4 FOOT,CABINET:BLACK POLYURETHANE 80009 34801870018 211040800 1 SCR,ASSEM WSHR:440 X 0.250,PNH,STL,CDPL,
19 131362701 7 CONTACT,ELEC:GOLD PLATED TIP
20 205019100 1 SHELL,ELEC CONN:BNC,ABS,DOVE GRAY
21 174346201 1 CABLE ASSY:CABLE W/COMP BOX 80009 17434620122 311253300 1 RES,VAR,P ANEL:CERMET;50K OHM,10%,1.0W,LINEAR
23 210000400 5 WASHER,LOCK:#4 INTL,0.015 THK,STL 78189 12040000054124 211039400
Tektronix Part Number
Serial No. Effective
Serial No.
Discontd
Qty Name & Description
W/SET SCREWS
POZ
(EXCHANGE ONLY)
0.385 H,30 GOLD,BLACK,JUMPER (SUBPAR T OF 22–9)
T–15 TORX DR,MACHINE
T–10 TORX DR
(SUBPAR T OF 22–21)
(SUBPAR T OF 22–21)
TAPER,12.5 MM SQ,0.375DIA X 0.375 L BUSHING, SOLDER LUGS
5
SCREW,MACHINE:4–40 X 0.875,PNH,STL CD PL TORX, T10
Mfr. Code
80009 366186103
80009 211054100
22526 65474–006
0KB01 ORDER BY DESC
0KB01 211–0408–00
18359 P–6158–1
80009 205019100
32997 53AAA–B24–A18R7
93907
Mfr. Part Number
B20–69595–003
58
159–0024–00 070–9164–xx
P6101B
STANDARD ACCESSORIES
2
FUSE,CARTRIDGE:3AG,0.062A,250V,0.3SEC
1
MANUAL,TECH:INSTRUCTION,ADA400A,DP
OPTIONAL ACCESSORIES
1
PROBE,PASSIVE:15MHZ 1X 2.0M
71400 80009
80009
AGC 1/16 0709164xx
P6101B
ADA400A Differential Preamplifier
Replaceable Parts
3
2
1
4
5 6
5 6
24 23
7
8 9
11
10
19
21
20
18
22
17
15
12
13
14
16
1
Figure 22: ADA400A Differential Preamplifier — Exploded View
ADA400A Differential Preamplifier
59
Replaceable Parts
60
ADA400A Differential Preamplifier

Glossary

Alternating Current (AC)
An electric current whose instantaneous value and direction change periodically.
Amplitude
The difference between a high and a low point on a waveform. Signal amplitude can be measured in terms of “peak-to-peak” or “peak” for example.
Attenuation
The degree the amplitude of a signal is reduced when it passes through an attenuating device such as a probe or attenuator. That is, the ratio of the input measure to the output measure. For example, a 10X attenuator will attenuate, or reduce, the input voltage of a signal by a factor of 10.
Bandwidth
Bandwidth is the specified frequency range of the vertical system wherein the vertical response is greater than or equal to 0.707 (–3dB) of the specified frequency down to DC or 0 Hz.
Common mode
Signals on both preamplifier inputs that are identical in voltage and phase.
Common-Mode Rejection Ratio (CMRR)
The extent to which a differential amplifier rejects a common-mode voltage presented on the inputs. CMRR is the ratio of the differential gain to the common-mode gain and is usually expressed in decibels (dB).
Coupling
The method of connecting the input circuit to the signal source. A coupling circuit, for example, may pass only AC signals above a certain frequency.
Differential
Signals that are not identical in amplitude or phase and thereby present a difference on the inputs of the preamplifier.
Direct Current
An electric current that flows in only one direction with essentially constant value.
Frequency
A timing measurement that is the reciprocal of the period. Frequency is measured in Hertz (Hz) where 1 Hz = 1 cycle per second.
Floating
A signal or voltage that does not have a reference to ground.
ADA400A Differential Preamplifier
61
Glossary
Gain
Increase in signal strength.
Ground
A connection or reference to the zero voltage potential of earth ground.
Ground loop
Two or more paths between grounded points in a circuit in which a current circulates. This current may induce a voltage potential which corrupts sensitive measurements.
Hertz
The unit of frequency, one cycle per second.
Megahertz (MHz)
6
A frequency of one million Hz (cycles per second), or 10
Hz.
Noise
An unwanted voltage or current in an electrical signal.
Normal mode
The signal of interest without the common-mode element.
Peak
The difference in amplitude between the maximum value and the average or mean value of a waveform.
Peak-to-Peak
Amplitude measurement of the absolute difference between the maximum and minimum amplitude.
Period
A timing measurement of the time covered by one complete signal cycle. It is the reciprocal of frequency and is measured in seconds.
Phase
A timing measurement between two waveforms of the amount one leads or lags the other. Phase is expressed in degrees where 360_ comprises one complete cycle of one of the waveforms.
62
RMS
Amplitude (voltage) measurement of the true Root-Mean-Square voltage.
Single ended
A connection to one input of the preamplifier only. The coupling of the other side must be set to ground (GND).
Waveform
The shape or form (visible representation) of a signal expressed as amplitude versus time (Y-T).
ADA400A Differential Preamplifier

Index

A
accessories
recommended, 2 standard, 1
adjustment procedures, 37
CMRR, 43 equipment required, 29 gain, 40 LF CMRR, 42 LF compensation, 44 zero offset, 41
B
bandwidth limit, 18, 53 block diagram, 52
C
cable housing, procedure for replacing, 51 checks, functional, 4 cleaning, 48 clipping, 16 common-mode rejection, 14 connections
differential, 14 input, 11–15
single-ended, 13 connectors, illustrated, 8 controls
offset, 18, 53
overview , 7–10 cover, procedure for removing, 50
D
F
fuses, 50
location of, 8
G
gain, 16, 53 ground loops, 15
H
housing, procedure for removing, 50
I
input
common-mode range, 16 differential range, 16
input coupling, 15, 53
oscilloscope, 4, 15 precharging, 16
input impedance
oscilloscope, 4, 15
preamplifier, 12, 53 input protection, 53 input range, 16 installation, 2 interference, 19
J
jumper
input impedance, 12
scale-factor coding, 2
diagnostic procedures, 54
E
effective volts/division, 10 electrostatic discharge, preventing, 47
ADA400A Differential Preamplifier
M
maintenance, 47–54
O
offset range, 16 overrange detection circuit, 53 overrange indicator, 9, 16
63
Index
P
parts
list of replaceable, 55–60 replacement of. See Maintenance
performance verification, 29
CMRR, 33 equipment required, 29 gain, 31
input resistance, 31 potentiometers, procedure for replacing, 50 procedures, performance verification, 29
R
repackaging, 54 replacement procedures, 48
S
safety , general summary, iii scale-factor coding, 53 shield, procedure for removing, 50 signal distortion, 16
T
TEKPROBE interface, 53
installation, 2 replacing interface collar, 49 replacing pins, 48
troubleshooting, 54
W
warranty service, 47
64
ADA400A Differential Preamplifier
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