Service Manual
1502C
Metallic Time-Domain Reflectometer
070-7168-04
This document applies to firmware version 5.02
and above.
Warning
The servicing instructions are for use by qualified
personnel only. To avoid personal injury, do not
perform any servicing unless you are qualified to
do so. Refer to all safety summaries prior to
performing service.
www.tektronix.com
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 the products that it manufactures and sells will be free from defects in materials and workmanship
for a period of one (1) year from the date of shipment. If a 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; c) to repair any damage or malfunction
caused by the use of non-T ektronix supplies; or d) 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 IN LIEU OF ANY OTHER WARRANTIES, EXPRESS OR
IMPLIED. TEKTRONIX AND ITS VENDORS DISCLAIM ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. TEKTRONIX’ RESPONSIBILITY TO
REP AIR OR REPLACE DEFECTIVE PRODUCTS IS THE SOLE AND EXCLUSIVE REMEDY PROVIDED TO
THE CUSTOMER 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 xi. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Service Safety Summary xiii. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
General Information xv. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Installation and Repacking xvi. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Contacting T ektronix xviii. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Operating Instructions
Operating Instructions 1–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Overview 1–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Preparing to Use the 1502C 1–5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Display 1–6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Front-Panel Controls 1–6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Menu Selections 1–7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
T est Preparations 1–11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Cable T est Procedure 1–13. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Additional Features (Menu Selected) 1–26. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Operator Performance Checks
Operator Performance Checks 2–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Specifications
Specifications 3–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Electrical Characteristics 3–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Environmental Characteristics 3–3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Certifications and Compliances 3–4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Physical Characteristics 3–5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Options and Accessories
Options and Accessories 4–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Option 04: YT–1 Chart Recorder 4–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Option 05: Metric Default 4–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Option 07: YT–1S Chart Recorder 4–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Power Cord Options 4–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Accessories 4–2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Circuit Descriptions
Circuit Descriptions 5–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Introduction 5–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Power Supply 5–4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1502C MTDR Service Manual
i
Table of Contents
Processor System 5–7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Option Port Interface 5–10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Video Processor 5–13. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Timebase 5–15. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Driver/Sampler 5–23. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Front Panel 5–25. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Display Module 5–28. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Calibration and Adjustments
Calibration 6–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Introduction 6–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Calibration Performance Check 6–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Display Module Check 6–2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Front Panel Check 6–4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Horizontal Scale (Timebase) Check 6–7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Zero Offset Check 6–10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Vertical Position (Offset) Check 6–12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Noise Check 6–13. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Sampling Efficiency Check 6–15. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Offset/Gain Check 6–16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
RAM/ROM Check 6–17. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Aberrations Check 6–17. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Risetime Check 6–19. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Jitter Check 6–21. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Option 04/07: YT-1/YT -1S Chart Recorder Check 6–23. . . . . . . . . . . . . . . . . . . . . . .
Option 05: Metric Default Check 6–23. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Adjustment Procedures 6–25. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Visual Inspection 6–26. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Power Supply Checks and Adjustments 6–26. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Main Board ”12 VDC Check and Adjust 6–30. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Impedance Check 6–35. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
LCD Check and Adjustment 6–36. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Zero Offset Adjust 6–39. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
After Adjustments are Completed 6–41. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Maintenance
ii
Maintenance 7–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Introduction 7–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Preventive Maintenance 7–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Part Removal and Replacement 7–2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Troubleshooting 7–12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Control Panel Installation 7–17. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Installing the Case Cover Over the Chassis 7–19. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1502C MTDR Service Manual
Replaceable Electrical Parts
Replaceable Electrical Parts 8–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Parts Ordering Information 8–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Diagrams
Diagrams 9–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
General Information 9–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Replaceable Mechanical Parts
Replaceable Mechanical Parts 10–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Parts Ordering Information 10–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Using the Replaceable Mechanical Parts List 10–1. . . . . . . . . . . . . . . . . . . . . . . . . . .
Glossary and Index
Table of Contents
1502C MTDR Service Manual
iii
Table of Contents
List of Figures
Figure 1–1: Rear Panel Voltage Selector, Fuse, AC Receptacle 1–1. . . . .
Figure 1–2: Display Showing Low Battery Indication 1–4. . . . . . . . . . . .
Figure 1–3: 1502C Front-Panel Controls 1–5. . . . . . . . . . . . . . . . . . . . . .
Figure 1–4: Display and Indicators 1–6. . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 1–5: Vp Set at .30, Cursor Beyond Reflected Pulse
(Set Too Low) 1–12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 1–6: Vp Set at .99, Cursor Less Than Reflected Pulse
(Set Too High) 1–12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 1–7: Vp Set at .66, Cursor at Reflected Pulse (Set Correctly) 1–12
Figure 1–8: 20-ft Cable at 5 ft/div 1–13. . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 1–9: Short in the Cable 1–13. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 1–10: Open in the Cable 1–14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 1–11: 455-ft Cable 1–14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 1–12: 455-ft Cable 1–15. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 1–13: Reflection Adjusted to One Division in Height 1–15. . . . . . .
Figure 1–14: Return Loss 1–17. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 1–15: Ohms-at-Cursor 1–17. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 1–16: Display with VIEW INPUT Turned Off 1–18. . . . . . . . . . . . .
Figure 1–17: Display of a Stored Waveform 1–19. . . . . . . . . . . . . . . . . . . .
Figure 1–18: Display of a Stored Waveform 1–19. . . . . . . . . . . . . . . . . . . .
Figure 1–19: Waveform Moved to Top Half of Display 1–20. . . . . . . . . . . .
Figure 1–20: Current Waveform Centered, Stored Waveform Above 1–20.
Figure 1–21: Current Waveform Center, Stored Waveform Above,
Difference Below 1–21. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 1–22: Waveform of Three-Foot Lead-in Cable 1–22. . . . . . . . . . . . .
Figure 1–23: Cursor Moved to End of Three-Foot Lead-in Cable 1–22. . . .
Figure 1–24: Cursor Moved to End of Three-Foot Lead-in Cable 1–23. . . .
Figure 1–25: Cursor Moved to 0.00 ft 1–23. . . . . . . . . . . . . . . . . . . . . . . . .
Figure 1–26: Incident Pulse at Three Divisions 1–24. . . . . . . . . . . . . . . . . .
Figure 1–27: Waveform of Short 75W Cable 1–24. . . . . . . . . . . . . . . . . . . .
Figure 1–28: Waveform Centered and Adjusted Vertically 1–25. . . . . . . . .
Figure 1–29: Cursor Moved to Desired Position 1–25. . . . . . . . . . . . . . . . .
Figure 1–30: Waveform Viewed in Normal Operation 1–26. . . . . . . . . . . . .
Figure 1–31: Waveform Showing Intermittent Changes 1–27. . . . . . . . . . .
Figure 1–32: Waveform Display with No Outgoing Pulses 1–27. . . . . . . . .
Figure 1–33: A Captured Single Sweep 1–29. . . . . . . . . . . . . . . . . . . . . . . .
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1502C MTDR Service Manual
Table of Contents
Figure 2–1: Start-up Measurement Display 2–2. . . . . . . . . . . . . . . . . . . .
Figure 2–2: Measurement Display with 3-foot Cable 2–2. . . . . . . . . . . .
Figure 2–3: Cursor at End of 3-foot Cable 2–3. . . . . . . . . . . . . . . . . . . . .
Figure 2–4: Flat-Line Display Out to 50,000+ Feet 2–3. . . . . . . . . . . . . .
Figure 2–5: Flat-Line Display at –2.000 ft 2–4. . . . . . . . . . . . . . . . . . . . .
Figure 2–6: Waveform Off the Top of the Display 2–4. . . . . . . . . . . . . . .
Figure 2–7: Waveform at the Bottom of the Display 2–5. . . . . . . . . . . . .
Figure 2–8: Waveform with Gain at 5.00 mr/div 2–5. . . . . . . . . . . . . . .
Figure 2–9: Top of Pulse on Center Graticule 2–7. . . . . . . . . . . . . . . . . .
Figure 2–10: Rising Edge of Incident Pulse in Left-most
Major Division 2–7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 2–11: Waveform Centered, Cursor at 0.000 ft 2–8. . . . . . . . . . . . .
Figure 2–12: Pulse Centered on Display 2–8. . . . . . . . . . . . . . . . . . . . . . .
Figure 2–13: Cursor on Lowest Major Graticule that Rising
Edge Crosses 2–9. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 2–14: Cursor on Highest Major Graticule that Rising
Edge Crosses 2–9. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 2–15: Jitter Apparent on Leading Edge of Incident Pulse 2–10. . . .
Figure 2–16: Jitter Captured Using Max Hold 2–10. . . . . . . . . . . . . . . . . . .
Figure 5–1: System Block Diagram 5–2. . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 5–2: Waveform Accumulation Diagram 5–3. . . . . . . . . . . . . . . . .
Figure 5–3: Power Supply Block Diagram 5–4. . . . . . . . . . . . . . . . . . . . .
Figure 5–4: Processor Block Diagram 5–8. . . . . . . . . . . . . . . . . . . . . . . .
Figure 5–5: Option Port Interface Block Diagram 5–11. . . . . . . . . . . . . . .
Figure 5–6: Video Processor Block Diagram 5–13. . . . . . . . . . . . . . . . . . .
Figure 5–7: Video Processor Output 5–15. . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 5–8: Timebase Block Diagram 5–16. . . . . . . . . . . . . . . . . . . . . . . .
Figure 5–9: Timebase Control 5–17. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 5–10: Combined Effects of Time Delay 5–18. . . . . . . . . . . . . . . . . .
Figure 5–11: Calibration of Delay Zero and 50-ns Analog Delay 5–19. . . .
Figure 5–12: Driver/Sampler Block Diagram 5–24. . . . . . . . . . . . . . . . . . .
Figure 5–13: Front Panel Block Diagram 5–26. . . . . . . . . . . . . . . . . . . . . . .
Figure 5–14: Display Module Block Diagram 5–29. . . . . . . . . . . . . . . . . . .
Figure 5–15: SBE Cell 5–30. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 5–16: Row Driver Block Diagram 5–31. . . . . . . . . . . . . . . . . . . . . .
Figure 5–17: Column Driver Block Diagram 5–32. . . . . . . . . . . . . . . . . . . .
Figure 5–18: Row Timing Diagram 5–33. . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 5–19: Column Timing Diagram 5–35. . . . . . . . . . . . . . . . . . . . . . . .
1502C MTDR Service Manual
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Table of Contents
Figure 5–20: Shift Register 5–36. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 5–21: CPU and Display Memory Interface 5–39. . . . . . . . . . . . . . . .
Figure 6–1: Typical Start-Up Display 6–2. . . . . . . . . . . . . . . . . . . . . . . . .
Figure 6–2: Waveform on the Display 6–2. . . . . . . . . . . . . . . . . . . . . . . .
Figure 6–3: Setup Menu 6–3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 6–4: Main Menu 6–4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 6–5: Diagnostics Menu 6–5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 6–6: Front Panel Diagnostic Display 6–5. . . . . . . . . . . . . . . . . . . .
Figure 6–7: Front Panel Diagnostic Display 6–6. . . . . . . . . . . . . . . . . . . .
Figure 6–8: Front Panel Diagnostic Display 6–6. . . . . . . . . . . . . . . . . . . .
Figure 6–9: Front Panel Diagnostic Display 6–7. . . . . . . . . . . . . . . . . . . .
Figure 6–10: Waveform on the Display with No Cable Attached 6–8. . . .
Figure 6–11: Display with 3-ft Cable and Stored Waveform 6–8. . . . . . . .
Figure 6–12: Cursor on Rising Edge of Pulse 6–9. . . . . . . . . . . . . . . . . . .
Figure 6–13: Cursor at 0.000 ft n 6–9. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 6–14: Cursor on Rising Edge of Pulse 6–9. . . . . . . . . . . . . . . . . . .
Figure 6–15: Flatline Display to >2,000 ft 6–10. . . . . . . . . . . . . . . . . . . . . .
Figure 6–16: Incident Pulse at –2.000 ft 6–11. . . . . . . . . . . . . . . . . . . . . . . .
Figure 6–17: Incident Pulse at –2.000 ft with 3-ft Cable Connected 6–11. .
Figure 6–18: Incident Pulse at –2.000 ft with Max Hold 6–11. . . . . . . . . . .
Figure 6–19: Waveform at Top of the Display 6–12. . . . . . . . . . . . . . . . . .
Figure 6–20: Waveform at Bottom of the Display 6–13. . . . . . . . . . . . . . . .
Figure 6–21: Waveform at Centered 6–13. . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 6–22: Cursor Moved to 100.000 ft 6–14. . . . . . . . . . . . . . . . . . . . . .
Figure 6–23: Noise with Gain at 5.00 mr 6–14. . . . . . . . . . . . . . . . . . . . . .
Figure 6–24: Noise Diagnostic Display 6–15. . . . . . . . . . . . . . . . . . . . . . . .
Figure 6–25: Service Diagnostic Menu 6–15. . . . . . . . . . . . . . . . . . . . . . . .
Figure 6–26: Sampling Efficiency Diagnostic 6–16. . . . . . . . . . . . . . . . . . .
Figure 6–27: Service Diagnostic Menu 6–16. . . . . . . . . . . . . . . . . . . . . . . .
Figure 6–28: Service Diagnostic Menu 6–17. . . . . . . . . . . . . . . . . . . . . . . .
Figure 6–29: Waveform with Cursor at –2.000 ft 6–18. . . . . . . . . . . . . . . . .
Figure 6–30: Waveform at 50 mr/div 6–18. . . . . . . . . . . . . . . . . . . . . . . . .
Figure 6–31: Waveform at 5 mr/div 6–19. . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 6–32: Incident Pulse at Center of Display 6–19. . . . . . . . . . . . . . . . .
Figure 6–33: Incident Pulse Centered, Vertical Increased 6–20. . . . . . . . . .
Figure 6–34: Cursor on Rising Edge at First Horizontal Graticule 6–20. . .
Figure 6–35: Cursor on Rising Edge at Last Horizontal Graticule 6–21. . .
Figure 6–36: Rising Edge at Center of Display 6–22. . . . . . . . . . . . . . . . . .
vi
1502C MTDR Service Manual
Table of Contents
Figure 6–37: Rising Edge with Scale at 1.0 mr/div 6–22. . . . . . . . . . . . . . .
Figure 6–38: Rising Edge with Max Hold on 6–22. . . . . . . . . . . . . . . . . . . .
Figure 6–39: Head Alignment Chart Print 6–23. . . . . . . . . . . . . . . . . . . . . .
Figure 6–40: Circuit Board Locations in the Instrument 6–25. . . . . . . . . . .
Figure 6–41: Power Supply Board 6–27. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 6–42: Power Supply Test Points TP1020 and TP1010 6–27. . . . . .
Figure 6–43: Power Supply Test Point TP2030 6–28. . . . . . . . . . . . . . . . .
Figure 6–44: Connector Plug P5040 and Pins J5040 on Bottom of
Main Board 6–29. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 6–45: Power Supply Test Point TP1020 6–29. . . . . . . . . . . . . . . . .
Figure 6–46: Power Supply Test Point TP2030 6–30. . . . . . . . . . . . . . . . .
Figure 6–47: Location of Main Board in Instrument 6–30. . . . . . . . . . . . . .
Figure 6–48: Main Board Probe Points 6–31. . . . . . . . . . . . . . . . . . . . . . . .
Figure 6–49: Waveform on Display 6–31. . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 6–50: Battery Connections to Power Supply Board 6–32. . . . . . . . .
Figure 6–51: CR2012 on Power Supply Board 6–33. . . . . . . . . . . . . . . . . .
Figure 6–52: Display Showing Power is Battery 6–33. . . . . . . . . . . . . . . . .
Figure 6–53: Display Showing Battery Voltage is Low 6–33. . . . . . . . . . . .
Figure 6–54: R2012 on Power Supply Board 6–34. . . . . . . . . . . . . . . . . . . .
Figure 6–55: Driver/Sampler Board Location 6–35. . . . . . . . . . . . . . . . . . .
Figure 6–56: TP1030 on Driver/Sampler Board 6–35. . . . . . . . . . . . . . . . .
Figure 6–57: R1018 on Front Panel Board 6–36. . . . . . . . . . . . . . . . . . . . . .
Figure 6–58: LCD Pattern with Contrast Too Light 6–36. . . . . . . . . . . . . . .
Figure 6–59: LCD Pattern with Contrast Too Dark 6–37. . . . . . . . . . . . . . .
Figure 6–60: LCD Pattern Adjusted for Sharpness 6–37. . . . . . . . . . . . . . .
Figure 6–61: Waveform with Contrast Too Light 6–38. . . . . . . . . . . . . . . . .
Figure 6–62: Waveform with Contrast Adjusted Correctly 6–38. . . . . . . . .
Figure 6–63: Driver/Sampler Board Location 6–39. . . . . . . . . . . . . . . . . . .
Figure 6–64: Incident Pulse at –2.000 ft 6–40. . . . . . . . . . . . . . . . . . . . . . . .
Figure 6–65: R1042 on Driver/Sampler Board 6–40. . . . . . . . . . . . . . . . . .
1502C MTDR Service Manual
Figure 7–1: Location of Voltage Selector and Fuse Holder on
Rear Panel 7–2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 7–2: Power Supply Module and P/O Rear Panel 7–4. . . . . . . . . .
Figure 7–3: Main Board 7–7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 7–4: EPROM on Main Board 7–7. . . . . . . . . . . . . . . . . . . . . . . . .
Figure 7–5: Lithium Battery on Main Board 7–8. . . . . . . . . . . . . . . . . . .
Figure 7–6: Display Module/Front Panel Board Screw Locations 7–10. . .
Figure 7–7: Display Module/Front Panel Board Showing Hex Nuts 7–10.
vii
Table of Contents
Figure 7–8: Location of Default Jumper on Front Panel Board 7–11. . . . .
Figure 7–9: Default Jumper Positions 7–11. . . . . . . . . . . . . . . . . . . . . . . .
Figure 7–10: Main Board TP1041 and TP3040 7–16. . . . . . . . . . . . . . . . . .
Figure 7–11: Main Board TP3041 and TP4040 7–16. . . . . . . . . . . . . . . . . .
Figure 7–12: Main Board TP6010 and TP7010 7–16. . . . . . . . . . . . . . . . . .
Figure 7–13: Main Board TP9011 and TP9041 7–17. . . . . . . . . . . . . . . . . .
Figure 7–14: Front Panel CABLE Connector 7–17. . . . . . . . . . . . . . . . . . .
Figure 7–15: Installing the Case Cover Over the Chassis 7–19. . . . . . . . . .
Figure 9–1: Special Schematic Symbols 9–3. . . . . . . . . . . . . . . . . . . . . .
Figure 9–2: Component Locator – Main Board 9–13. . . . . . . . . . . . . . . . .
Schematics – Main Board 9–14. . . . . . . . . . . . . . . . . . . . . . . .
Figure 9–3: Component Locator – Front Panel Board 9–23. . . . . . . . . . . .
Schematics – Front Panel 9–24. . . . . . . . . . . . . . . . . . . . . . . .
Figure 9–4: Component Locator – Power Supply Board 9–26. . . . . . . . . .
Schematics – Power Supply 9–27. . . . . . . . . . . . . . . . . . . . . .
Figure 9–5: Component Locator – Driver/Sampler Board 9–29. . . . . . . . .
Schematics – Driver/Sampler 9–30. . . . . . . . . . . . . . . . . . . . .
Figure 10–1: Cabinet 10–13. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 10–2: Frame, Assemblies and Front Panel Controls 10–15. . . . . . . . .
Figure 10–3: Power Supply 10–17. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
viii
1502C MTDR Service Manual
List of Tables
Table of Contents
Shipping Carton Test Strength xv. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Fuse / Voltage Ratings 1–2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Vp of Various Dielectric Types 1–11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Operator Performance Checks – Equipment Required 2–1. . . . . . . . . . . . . . .
Specifications: Electrical Characteristics 3–1. . . . . . . . . . . . . . . . . . . . . . . . .
Specifications: Environmental Characteristics 3–3. . . . . . . . . . . . . . . . . . . . .
Certifications and Compliances 3–4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Specifications: Physical Characteristics 3–5. . . . . . . . . . . . . . . . . . . . . . . . . .
Option Port Wiring Configuration 5–12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Row Driver Latch Bits 5–34. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Column Driver Latch Bits 5–36. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Controller Periods 5–37. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Calibration Performance Check – Equipment Required 6–1. . . . . . . . . . . . . .
Adjustment Procedures – Equipment Required 6–25. . . . . . . . . . . . . . . . . . . .
Main Board Voltages, Tolerances, Test Point Locations 6–28. . . . . . . . . . . . . .
Maintenance – Equipment Required 7–1. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Power Cord Conductor Color Code 7–6. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Sealing Materials 7–18. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1502C MTDR Service Manual
ix
Table of Contents
x
1502C MTDR Service Manual
General Safety Summary
Review the following safety precautions to avoid injury and prevent damage to
this product or any products connected to it. To avoid potential hazards, use this
product only as specified.
Only qualified personnel should perform service procedures.
To Avoid Fire or Personal Injury
Power Source
Use Proper Power Cord. Use only the power cord specified for this product and
certified for the country of use.
Use Proper V oltage Setting. Before applying power, ensure that the line selector is
in the proper position for the power source being used.
This product is intended to operate from a power source that will not apply more than
250 volts RMS between the supply conductors or between the supply conductor and
ground. A protective ground connection, by way of the grounding conductor in the
power cord, is essential for safe operation.
Ground the Product. This product is grounded through the grounding conductor
of the power cord. To avoid electric shock, the grounding conductor must be
connected to earth ground. Before making connections to the input or output
terminals of the product, ensure that the product is properly grounded.
The standard power cord (161–0288–00) is rated for outdoor use. All other optional
power cords are rated for indoor use only.
Observe All Terminal Ratings. To avoid fire or shock hazard, observe all ratings
and markings on the product. Consult the product manual for further ratings
information before making connections to the product.
Do not apply a potential to any terminal, including the common terminal, that
exceeds the maximum rating of that terminal.
1502C MTDR Service Manual
Replace Batteries Properly. Replace batteries only with the proper type and rating
specified.
Recharge Batteries Properly. Recharge batteries for the recommended charge
cycle only.
Use Proper AC Adapter. Use only the AC adapter specified for this product.
Do Not Operate Without Covers. Do not operate this product with covers or panels
removed.
Use Proper Fuse. Use only the fuse type and rating specified for this product.
Avoid Exposed Circuitry. Do not touch exposed connections and components
when power is present.
xi
General Safety Summary
Do Not Operate With Suspected Failures. If you suspect there is damage to this
product, have it inspected by qualified service personnel.
Do Not Operate in an Explosive Atmosphere.
Symbols and Terms
T erms in this Manual. These terms may appear in this manual:
WARNING. Warning statements identify conditions or practices that could result
in injury or loss of life.
CAUTION. Caution statements identify conditions or practices that could result in
damage to this product or other property.
T erms on the Product. 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. The following symbols may appear on the product:
xii
CAUTION
Refer to Manual
WARNING
High Voltage
Double
Insulated
Protective Ground
(Earth) Terminal
1502C MTDR Service Manual
Service Safety Summary
Only qualified personnel should perform service procedures. Read this Service
Safety Summary and the General Safety Summary before performing any service
procedures.
Do Not Service Alone
Disconnect Power
Use Care When Servicing
With Power On
Disposal of Batteries
Do not perform internal service or adjustments of this product unless another person
capable of rendering first aid and resuscitation is present.
T o avoid electric shock, disconnect the main power by means of the power cord or
the power switch.
Dangerous voltages or currents may exist in this product. Disconnect power, remove
battery, and disconnect test leads before removing protective panels, soldering, or
replacing components.
To avoid electric shock, do not touch exposed connections.
This instrument contains a lead-acid battery . Some states and/or local jurisdictions
might require special disposition/recycling of this type of material in accordance
with Hazardous Waste guidelines. Check your local and state regulations prior to
disposing of an old battery.
T ektronix Factory Service will accept 1502C batteries for recycling. If you choose
to return the battery to us for recycling, the battery cases must be intact, the battery
should be packed with the battery terminals insulated against possible short-circuits,
and should be packed in shock-absorbant material.
1502C MTDR Service Manual
Tektronix, Inc.
Attn: Service Department
P.O. Box 500
Beaverton, Oregon 97077 U.S.A.
For additional information, phone:1-800-TEK-WIDE
xiii
Service Safety Summary
xiv
1502C MTDR Service Manual
General Information
Product Description
Battery Operation
Options
The Tektronix 1502C Metallic-cable Time-Domain Reflectometer (MTDR) is a
cable test instrument that uses radar principles to determine the electrical
characteristics of metallic cables.
The 1502C generates a half-sine wave signal, applies it to the cable under test, and
detects and processes the reflected voltage waveform. These reflections are
displayed in the 1502C liquid crystal display (LCD), where distance measurements
may be made using a cursor technique. Impedance information may be obtained
through interpreting waveform amplitude.
The waveform may be temporarily stored within the 1502C and recalled or may be
printed using the optional dot matrix strip chart recorder, which installs into the
front-panel Option Port.
The 1502C may be operated from an AC power source or an internal lead-gel
battery, which supplies a minimum of eight hours operating time (see the
Specifications chapter for specifics).
Options available for the 1502C are explained in the Options and Accessories
chapter of this manual.
Standards, Documents,
and References Used
Changes and History
Information
1502C MTDR Service Manual
Terminology used in this manual is in accordance with industry practice.
Abbreviations are in accordance with ANSI Y1.1–19722, with exceptions and
additions explained in parentheses in the text. Graphic symbology is based on ANSI
Y32.2–1975. Logic symbology is based on ANSI Y32.14–1973 and manufacturer’s
data books or sheets. A copy of ANSI standards may be obtained from the Institute
of Electrical and Electronic Engineers, 345 47th Street, New York, NY 10017.
Changes that involve manual corrections and/or additional data will be incorporated
into the text and that page will show a revision date on the inside bottom edge.
History information is included in any diagrams in gray.
xv
General Information
Installation and Repacking
Unpacking and InItial
Inspection
Power Source and Power
Requirements
Before unpacking the 1502C from its shipping container or carton, inspect for signs
of external damage. If the carton is damaged, notify the carrier. The shipping carton
contains the basic instrument and its standard accessories. Refer to the replaceable
parts list in the Service Manual for a complete listing.
If the contents of the shipping container are incomplete, if there is mechanical
damage or defect, or if the instrument does not meet operational check requirements,
contact your local T ektronix Field Office or representative. If the shipping container
is damaged, notify the carrier as well as Tektronix.
The instrument was inspected both mechanically and electrically before shipment.
It should be free if mechanical damage and meet or exceed all electrical
specifications. Procedures to check operational performance are in the Performance
Checks appendix. These checks should satisfy the requirements for most receiving
or incoming inspections.
The 1502C is intended to be operated from a power source that will not apply more
than 250 volts RMS between the supply conductors or between either supply
conductor and ground. A protective ground connection, by way of the grounding
conductor in the power cord, is essential for safe operation.
The AC power connector is a three-way polarized plug with the ground (earth) lead
connected directly to the instrument frame to provide electrical shock protection. If
the unit is connected to any other power source, the unit frame must be connected
to earth ground.
Repacking for Shipment
xvi
Power and voltage requirements are printed on the back panel. The 1502C can be
operated from either 115 VAC or 230 VAC nominal line voltage at 45 Hz to 440 Hz,
or a 12 VDC supply, or an internal battery.
Further information on the 1502C power requirements can be found in the Safety
Summary in this section and in the Operating Instructions chapter.
When the 1502C is to be shipped to a T ektronix Service Center for service or repair,
attach a tag showing the name and address of the owner, name of the individual at
your firm who may be contacted, the complete serial number of the instrument, and
a description of the service required. If the original packaging is unfit for use or is
not available, repackage the instrument as follows:
1. Obtain a carton of corrugated cardboard having inside dimensions that are at
least six inches greater than the equipment dimensions to allow for cushioning.
The test strength of the shipping carton should be 275 pounds (102.5 kg). Refer
to the following table for test strength requirements:
1502C MTDR Service Manual
General Information
SHIPPING CARTON TEST STRENGTH
Gross Weight (lb)
0 – 10 200
11 – 30 275
31 – 120 375
121 – 140 500
141 – 160 600
CAUTION. The battery pack should be removed fr om the instrument before shipping.
If it is necessary to ship the battery, it should be wrapped and secured separately
before being packed with the instrument.
2. Install the front cover on the 1502C and surround the instrument with
polyethylene sheeting to protect the finish.
Carton Test Strength (lb)
3. Cushion the instrument on all sides with packing material or urethane foam
between the carton and the sides of the instrument.
4. Seal with shipping tape or an industrial stapler.
If you have any questions, contact your local Tektronix Field Office or
representative.
1502C MTDR Service Manual
xvii
General Information
Contacting Tektronix
Product
Support
Service
support
Toll-free
Number
Postal
Address
For questions about using Tektronix measurement products, call
toll free in North America:
1-800-833-9200
6:00 a.m. – 5:00 p.m. Pacific time
Or contact us by e-mail:
tm_app_supp@tek.com
For product support outside of North America, contact your local
Tektronix distributor or sales office.
T ektronix offers a range of services, including Extended Warranty
Repair and Calibration services. Contact your local Tektronix
distributor or sales office for details.
For a listing of worldwide service centers, visit our web site.
In North America:
1-800-833-9200
An operator can direct your call.
Tektronix, Inc.
Department or name (if known)
P.O. Box 500
Beaverton, OR 97077
USA
Web site www.tektronix.com
xviii
1502C MTDR Service Manual
Operating Instructions
Overview
Handling
Powering the 1502C
The 1502C front panel is protected by a watertight cover, in which the standard
accessories are stored. Secure the front cover by snapping the side latches outward.
If the instrument is inadvertently left on, installing the front cover will turn off the
POWER switch automatically.
The carrying handle rotates 325° and serves as a stand when positioned beneath the
instrument.
Inside the case, at the back of the instrument, is a moisture-absorbing canister
containing silica gel. In extremely wet environments, it might be be necessary to
periodically remove and dry the canister. This procedure is explained in the 1502C
Service Manual.
The 1502C can be stored in temperatures ranging from –62° C to +85° C. However,
if the temperature is below –40° C or above +55° C, the battery pack should be
removed and stored separately. Battery storage temperature should be –40° C to
+55° C.
In the field, the 1502C can be powered using the internal battery . For AC operation,
check the rear panel for proper voltage setting. The voltage selector can be seen
through the window of the protective cap. If the setting differs from the voltage
available, it can be easily changed. Simply remove the protective cap and select the
proper voltage using a screwdriver.
1502C MTDR Service Manual
REMOVE
CAP TO
SELECT
VOLTAGE
REMOVE
CAP TO
REPLACE
FUSE
Voltage
Selector
Line Fuse
AC Power
Cord Receptacle
Figure 1–1: Rear Panel Voltage Selector, Fuse, AC Receptacle
1–1
Operating Instructions
The 1502C is intended to be operated from a power source that will not apply more
than 250 V RMS between the supply conductors or between either supply conductor
and ground. A protective ground connection by way of the grounding conductor in
the power cord is essential for safe operation.
The AC power connector is a three-way polarized plug with the ground (earth) lead
connected to the instrument frame to provide electrical shock protection. If the unit
is connected to any other power source, the unit frame must be connected to an earth
ground. See Safety and Installation section.
CAUTION. If you change the voltage selector, you must change the line fuse to the
appropriate value as listed near the fuse holder and in the table below.
FUSE RATING VOLTAGE RATING
250 V NOMINAL RANGE
0.3 A T 115 VAC (90 – 132 VAC)
0.15 A T 230 VAC (180 – 250 VAC)
Care of the Battery Pack
Battery Charging
CAUTION. Read these instructions concerning the care of the battery pack. They
contain instructions that reflect on your safety and the performance of the
instrument.
The 1502C can be powered by a rechargeable lead-gel battery pack that is accessible
only by removing the case from the instrument. When AC power is applied, the
battery pack is charged at a rate that is dependent on the battery charge state.
The battery pack will operate the 1502C for a minimum of eight continuous hours
(including making 30 chart recordings) if the LCD backlight is turned off.
The battery pack will charge fully in 16 hours when the instrument is connected, via
the power cord, to an AC power source with the instrument turned off. The
instrument may be turned on and operated while the batteries are charging, but this
will increase the charging time. For longest battery life, a full charge is preferred
over a partial charge.
For maximum capacity , the batteries should be charged within a temperature range
of +20° C to +25° C. However, the batteries can be charged within a temperature
range of 0° C to +40° C and operated in temperatures ranging from –10° C to +55° C.
1–2
1502C MTDR Service Manual
Battery Removal
Operating Instructions
CAUTION. Do not charge battery pack below 0° C or above +40° C. Do not
discharge battery pack below –10° C or above +55° C. If r emoving the battery pack
during or after exposure to these extreme conditions, turn the instrument off and
remove the AC power cord.
The battery pack should be stored within a temperature range of –35° C to +65° C.
However, the self-discharge rate will increase as the temperature increases.
If the instrument is stored with the battery pack installed, the battery pack should
be charged every 90 days. A fully charged battery pack will lose about 12% of its
capacity in three to four months if stored between +20° C and +25° C.
NOTE. The battery pack in the 1502C is inside the instrument case with no external
access. Refer removal and replacement to qualified service personnel.
1. Ensure that the instrument power is off.
2. If the instrument is connected to an AC power source, remove the AC power
cable from the source and from the instrument.
3. If installed, remove the chart recorder, or other device, from the option port.
4. Loosen the four screws on the back of the case and set the instrument face-up
on a flat surface.
5. Swing the handle out of the way of the front panel.
6. Break the chassis seal by pushing downward with both hands on the handle
pivots on each side of the case.
7. Grasp the case with one hand and tilt the chassis out with the other. Lift by
grasping the outside perimeter of the front panel.
CAUTION. Do not lift the instrument by the front-panel controls. The controls will
be damaged if you do so.
8. Remove the top shield from the instrument by gently lifting the rear edge near
the sides of the instrument.
9. Unplug the battery cable positive lead at the battery.
1502C MTDR Service Manual
10. Unplug the battery cable negative lead at the battery.
11. Unplug the battery cable at the power supply.
12. Remove the cable.
1–3
Operating Instructions
13. Remove the two screws mounting the battery clamp to the chassis.
14. Carefully remove the clamp without touching the battery terminals.
15. Lift the battery out.
To re-install or replace the battery, repeat the above steps in reverse order.
Low Battery
If the battery is low, it will be indicated on the LCD (bat/low). If this is the case,
protective circuitry will shut down the 1502C within minutes. Either switch to AC
power or work very fast. If the instrument is equipped with a chart recorder, using
the recorder will further reduce the battery level, or the added load might shut down
the instrument.
bat/low 0.000 ft
O
N
O
F
F
O
F
F
O
F
F
1 avg
500 mr 500 ft
Low Battery
Indicator
Figure 1–2: Display Showing Low Battery Indication
Protection circuits in the charger prevent deep discharge of the batteries during
instrument operation. The circuits automatically shut down the instrument
whenever battery voltage falls below approximately 10 V. If shutdown occurs, the
batteries should be fully recharged before further use.
1–4
Low Temperature
Operation
NOTE. Turn the POWER switch off after instrument shutdown to prevent continued
discharge of the batteries.
Under low AC voltage conditions, AC fuse ratings might be exceeded if the battery
if fully discharged and a chart r ecor ding is being made. Allow the battery to charge
for about one hour before attempting to make a chart recording, or use AC only.
When operating the 1502C in an environment below +10° C, a heater will activate.
The element is built into the LCD module and will heat the display to permit normal
operation. Depending on the surrounding temperature, it might take up to 15
minutes to completely warm the crystals in the LCD. Once warmed, the display will
operate normally.
1502C MTDR Service Manual
Preparing to Use the 1502C
Check the power requirements, remove the front cover, and you are ready to test
cables. The following pages explain the front-panel controls.
Operating Instructions
11
12
10
13
8
7
9
0.2 ft
METALLIC TDR
CABLE TESTER
POSITION
POSITION
Vp
.5
.4
.3
.04
.6
.9
.05
.03
.7
.8
.06
.02
.07
.08
.01
.09
.00
POWER
(PULL ON)
1
MENU
VIEW
INPUT
VIEW
STORE
VIEW
DIFF
STORE
DO NOT APPLY
EXT VOLTAGE
Tektronix
1502B
ac 0.00 ft
O
N
O
F
F
O
F
F
O
F
F
1 avg
NOISE FILTER VERT SCALE DIST/DIV
HORZ
VERT
2
500 mr
SET REF
3 4 5 6
Figure 1–3: 1502C Front-Panel Controls
CAUTION. Do not connect live circuits to the CABLE connector. V oltages exceeding
5 volts can damage the driver or sampler circuits.
Bleed the test cable of any residual static charge before attaching it to the
instrument. To bleed the cable, connect the standard 50W terminator and standar d
female-to-female BNC connector together, then temporarily attach both to the
cable. Remove the connectors before attaching the cable to the instrument.
When testing receiving antenna cables, avoid close proximity to transmitters.
Voltages may appear on the cable if a nearby transmitter is in use, resulting in
damage to the instrument. Before testing, be sure that there are no RF voltages
present, or disconnect the cable at both ends.
1502C MTDR Service Manual
1–5
Operating Instructions
Display
Power
Type CursorWaveform
Front-Panel to Cursor
Distance Window
Front-Panel Controls
NOISE FILTER
HORZ
VERT SET REF
View Input
Indicator
View Store
Indicator
View Difference
Indicator
Store
Indicator
ac
O
N
O
F
F
O
F
F
O
F
F
1 avg
Selected
Noise Filter
500 mr 0.2 ft
Selected Selected
Vertical Scale Distance per
Division
0.000 ft
Figure 1–4: Display and Indicators
1. CABLE: A female BNC connector for attaching a cable to the 1502C for
testing.
2. NOISE FILTER: If the displayed waveform is noisy, the apparent noise can
be reduced by using noise averaging. A veraging settings are between 1 and 128.
The time for averaging is directly proportional to the averaging setting chosen.
A setting of 128 might take the instrument up to 35 seconds to acquire and
display a waveform. The first two positions on the NOISE FILTER control are
used for setting the vertical and horizontal reference points. The selected value
or function is displayed above the control on the LCD.
Grid
1–6
VERT SCALE
DIST/DIV
3. VERT SCALE: This control sets the vertical sensitivity, displayed in mr per
division, or the vertical gain, displayed in dB. Although the instrument defaults
to millirho, you may choose the preferred mode from the Setup Menu. The
selected value is displayed above the control on the LCD.
4. DIST/DIV: Determines the number of feet (or meters) per division across the
display. The minimum setting is 0.1 ft/div (0.025 meters) and the maximum
setting is 200 ft/div (50 meters). The selected value is displayed above the
control on the LCD.
A standard instrument defaults to ft/div. A metric instrument (Option 05)
defaults to m/div, but either may be changed temporarily from the menu. The
default can be changed by changing an internal jumper (see 1502C Service
Manual and always refer such changes to qualified service personnel).
1502C MTDR Service Manual
Operating Instructions
.3
.4 .5
POWER
(PULL ON)
n
o
n
o
Vp
.03
.6
.7
.02
.8
.01
.9 .00
POSITION
POSITION
MENU
.04 .05
5. Vp: The two Velocity of Propagation controls are set according to the
.06
.07
.08
.09
propagation velocity factor of the cable being tested. For example, solid
polyethylene commonly has a Vp of 0.66. Solid polytetraflourethylene (T eflon
) is approximately 0.70. Air is 0.99. The controls are decaded: the left control
is the first digit and the right control is the second digit. For example, with a Vp
of 0.30, the first knob would be set to .3 and the second knob to .00.
6. POWER: Pull for power ON and push in for power OFF . When the front cover
is installed, this switch is automatically pushed OFF.
n
7.
POSITION: This is a continuously rotating control that positions the
o
displayed waveform vertically, up or down the LCD.
n
o
8.
POSITION: This is a continuously rotating control that moves a vertical
cursor completely across the LCD graticule. In addition, the waveform is also
moved when the cursor reaches the extreme right or left side of the display. A
readout (seven digits maximum) is displayed in the upper right corner of the
LCD, showing the distance from the front panel BNC to the current cursor
location.
9. MENU: This pushbutton provides access to the menus and selects items chosen
from the menus.
VIEW
INPUT
VIEW
STORE
VIEW
DIFF
STORE
Menu Selections
Main Menu
10. VIEW INPUT: When pushed momentarily, this button toggles the display of
the waveform acquired at the CABLE connector. This function is useful to stop
displaying a current waveform to avoid confusion when looking at a stored
waveform. This function defaults to ON when the instrument is powered up.
11. VIEW STORE: When pushed momentarily, this button toggles the display of
the stored waveform.
12. VIEW DIFF: When pushed momentarily , this button toggles the display of the
current waveform minus the stored waveform and shows the difference between
them.
13. STORE: When pushed momentarily, the waveform currently displayed will be
stored in the instrument memory . If a waveform is already stored, pushing this
button will erase it. The settings of the stored waveform are available from the
first level menu under View Stored Waveform Settings.
There are several layers of menu, as explained below.
The Main Menu is entered by pushing the MENU button on the front panel.
1. Return to Normal Operations puts the instrument into normal operation
mode.
1502C MTDR Service Manual
1–7
Operating Instructions
2. Help with Instrument Controls explains the operation of each control. When
a control or switch is adjusted or pushed, a brief explanation appears on the
LCD.
3. Cable Information has these choices:
a. Help with Cables gives a brief explanation of cable parameters.
b. V elocity of Propagation V alues displays a table of common dielectrics and
their Vp values. These are nominal values. The manufacturer’s listed
specifications should be used whenever possible.
c. Impedance Values displays impedances of common cables. In some cases,
these values have been rounded off. Manufacturer’s specifications should
be checked for precise values.
d. Finding Unknown Vp Values describes a procedure for finding an
unknown Vp.
4. Setup Menu controls the manner in which the instrument obtains and displays
its test results.
a. Acquisition Control Menu has these choices:
i. Max Hold Is: On/Off. Turn Max Hold on by pushing MENU then
STORE. In this mode, waveforms are accumulated on the display . Max
Hold can be deactivated by pushing STORE or the mode exited by
using the Setup Menu.
ii. Pulse Is: On/Off. Turns the pulse generator off so the 1502C does not
send out pulses.
iii. Single Sweep Is: On/Off. This function is much like a still camera; it
will acquire one waveform and hold it.
b. Ohms-at-Cursor is: On/Off. When activated, the impedance at thee point
of the cursor is displayed beneath the distance window on the display.
c. Vertical Scale Is: dB/mr. This offers you a choice as to how the vertical
gain of the instrument is displayed. You may choose decibels or millirho.
When powered down, the instrument will default to millirho when powered
back up.
d. Distance/Div Is: ft/m. Offers you a choice of how the horizontal scale is
displayed. You may choose from feet per division or meters per division.
When powered up, the instrument will default to feet unless the internal
jumper has been moved to the meters position. Instructions on changing this
default are contained in the 1502C Service Manual.
1–8
e. Light Is: On/Off. This control turns the electroluminescent backlight
behind the LCD on or off.
1502C MTDR Service Manual
Operating Instructions
5. Diagnostics Menu lists an extensive selection of diagnostics to test the
operation of the instrument.
NOTE. The Diagnostics Menu is intended for instrument repair and calibration.
Proper instrument setup is important for correct diagnostics results. Refer to the
1502C Service Manual for more information on diagnostics.
a. Service Diagnostics Menu has these choices:
i. Sampling Efficiency Diagnostic displays a continuous efficiency
diagnostic of the sampling circuits.
ii. Noise Diagnostic measures the internal RMS noise levels of the
instrument.
iii. Offset/Gain Diagnostic reports out-of-tolerance steps in the program-
mable gain stage. This can help a service technician to quickly isolate
the cause of waveform distortion problems.
iv. RAM/ROM Diagnostics Menu performs tests on the RAM (Random
Access Memory) and the ROM (Read Only Memory).
v. Timebase Is: Normal - Auto Correction / Diagnostic - No
Correction. When in Normal - Auto Correction, the instrument
compensates for variations in temperature and voltage. This condition
might not be desirable while calibrating the instrument. While in
Diagnostic - No Correction, the circuits will not correct for these
variations.
b. Front Panel Diagnostics aids in testing the front panel.
c. LCD Diagnostics Menu has these choices:
i. LCD Alignment Diagnostic generates a dot pattern of every other
pixel on the LCD. These pixels can be alternated to test the LCD.
ii. Response Time Diagnostic generates alternate squares of dark and
light, reversing their order. This tests the response time of the LCD and
can give an indication of the effectiveness of the LCD heater in a cold
environment.
iii. LCD Drive Test Diagnostic generates a moving vertical bar pattern
across the LCD.
1502C MTDR Service Manual
iv. Contrast Adjust allows you to adjust the contrast of the LCD. It
generates an alternating four-pixel pattern. The nominal contrast is set
internally . When in Contrast Adjust mode, VERT SCALE is used as the
contrast adjustment control. This value ranges from 0 to 255 units and
1–9
Operating Instructions
is used by the processor to evaluate and correct circuit variations caused
by temperature changes in the environment. When the diagnostic menu
is exited, the LCD contrast returns to that set by internal adjust.
d. Chart Diagnostics Menu offers various tests for the optional chart
recorder.
i. LCD Chart allows adjusting the number of dots per segment and the
number of prints (strikes) per segment.
ii. Head Alignment Chart generates a pattern to allow mechanical
alignment of the optional chart recorder.
6. View Stored Waveform Settings displays the instrument settings for the stored
waveform.
7. Option Port Menu contains three items. Two items allow configuration of the
option port for communicating with devices other than the optional chart
recorder and one item test the option port.
a. Option Port Diagnostic creates a repeating pattern of signals at the option
port to allow service technicians to verify that all signals are present and
working correctly.
b. Set Option Port Timing allows adjustment of the data rate used to
communicate with external devices. The timing rate between bytes can be
set from about 0.05 to 12.8 milliseconds.
c. Option Port Debugging Is Off/On. Off is quiet, On is verbose. This
chooses how detailed the error message reporting will be when communicating with an external device.
It is possible to connect the instrument to a computer through a parallel interface
with a unique software driver. Because different computers vary widely in
processing speed, the instrument must be able to adapt to differing data rates
while communicating with those computers. With user-developed software
drivers, the ability to obtain detailed error messages during the development can
be very useful. For more information, contact your T ektronix Customer Service
representatives. They have information describing the option port hardware and
software protocol and custom development methods available.
8. Display Contrast (Software Version 5.02 and above)
a. Press the MENU button firmly once. If the display is very light or very dark,
you might not be able to see a change in the contrast.
b. Turn the VER TICAL SCALE knob slowly clockwise to darken the display
or counterclockwise to lighten the display . If you turn the knob far enough,
the contrast will wrap from the darkest to lightest value.
1–10
1502C MTDR Service Manual
Test Preparations
n
o
Operating Instructions
c. When the screen is clearly readable, press the MENU button again to return
to normal measurement operation. The new contrast value will remain in
effect until the instrument is turned off.
The Importance of Vp
(Velocity of Propagation)
Vp of Various Dielectric
Types
Vp is the speed of a signal down the cable given as a percentage of the speed of light
in free space. It is sometimes expressed as a whole number (e.g., 66) or a percentage
(e.g., 66%). On the 1502C, it is the percentage expressed as a decimal number (e.g.,
66% = .66). If you do not know the velocity of propagation, you can get a general
idea from the following table, or use the Help with Cables section of the Cable
Information menu. You can also find the Vp with the procedure that follows using
a cable sample.
NOTE. If you do not know the Vp of your cable, it will not prevent you fr om finding
a fault in your cable. However, if the Vp is set wrong, the distance readings will be
affected.
All Vp settings should be set for the cable under test, not the supplied jumper cable.
Dielectric Probable Vp
Jelly Filled .64
Polyethylene (PIC, PE, or SPE) .66
PTFE (Teflon R) or TFE .70
Pulp Insulation .72
Foam or Cellular PE (FPE) .78
Semi-solid PE (SSPE) .84
Air (helical spacers) .98
Finding an Unknown Vp
1. Obtain a known length of cable of the exact type you wish to test. Attach the
cable to the CABLE connector on the front panel.
2. Pull POWER on.
3. Turn the DIST/DIV to an appropriate setting (e.g., if trying to find the Vp of a
three-foot cable, turn the DIST/DIV to 1 ft/div).
4. Turn the
known length of this cable.
1502C MTDR Service Manual
POSITION control until the distance reading is the same as the
1–11
Operating Instructions
5. Turn the Vp controls until the cursor is resting on the rising portion of the
reflected pulse. The Vp controls of the instrument are now set to the Vp of the
cable.
The following three illustrations show settings too low, too high, and correct for a
sample three-foot cable.
ac 3.000 ft
O
N
O
F
F
O
F
F
O
F
F
Figure 1–5: Vp Set at .30, Cursor Beyond Reflected Pulse (Set Too Low)
ac 3.000 ft
O
N
O
F
F
O
F
F
O
F
F
Figure 1–6: Vp Set at .99, Cursor Less Than Reflected Pulse (Set T oo High)
ac 3.000 ft
O
N
O
F
F
O
F
F
O
F
F
Figure 1–7: Vp Set at .66, Cursor at Reflected Pulse (Set Correctly)
1–12
1502C MTDR Service Manual
Cable Test Procedure
Operating Instructions
Distance to the Fault
Be sure to read the previous paragraphs on Vp.
1. Set the 1502C controls:
POWER On
CABLE Cable to BNC
NOISE FILTER 1 avg
VERT SCALE 500 mr
DIST/DIV (see below)
Vp (per cable)
2. If you know approximately how long the cable is, set the DIST/DIV
appropriately (e.g., 20-ft cable would occupy four divisions on the LCD if 5
ft/div was used). The entire cable should be displayed.
ac 0.000 ft
O
N
O
F
F
O
F
F
O
F
F
Figure 1–8: 20-ft Cable at 5 ft/div
1502C MTDR Service Manual
If the cable length is unknown, set DIST/DIV to 200 ft/div and continue to decrease
the setting until the reflected pulse is visible. Depending on the cable length and the
amount of pulse energy absorbed by the cable, it might be necessary to increase the
VERT SCALE to provide more gain to see the reflected pulse.
ac 20.000 ft
O
N
O
F
F
Short
O
F
F
O
F
F
Figure 1–9: Short in the Cable
1–13
Operating Instructions
n
o
n
o
When the entire cable is displayed, you can tell if there is an open or a short.
Essentially, a large downward pulse indicates a short (see Figure 1–9, previous
page), while a large upward pulse indicates an open (see Figure 1–10). Less
catastrophic faults can bee seen as smaller reflections. Bends and kinks, frays, water,
and interweaving all have distinctive signatures.
ac 20.000 ft
O
N
O
F
F
O
F
F
O
F
F
Open
Figure 1–10: Open in the Cable
3. To find the distance to the fault or end of the cable, turn the
POSITION
control until the cursor rests on the leading edge of the rising or falling reflected
pulse (see Figure 1–10). Read the distance in the distance window in the upper
right corner of the display.
A more thorough inspection might be required. This example uses a longer cable:
4. When inspecting a 452-foot cable, a setting of 50 ft/div allows a relatively fast
inspection. If needed, turn VERT SCALE to increase the gain. The higher the
gain, the smaller the faults that can be detected. If noise increases, increase the
NOISE FILTER setting.
ac 452.000 ft
O
N
O
F
F
O
F
F
O
F
F
Open
Figure 1–11: 455-ft Cable
5. Change DIST/DIV to 20 ft/div. The entire cable can now be inspected in detail
on the LCD. Turn the
POSITION control so the cursor travels to the far right
side of the LCD. Keep turning and the cable will be “dragged” across the
display.
1–14
1502C MTDR Service Manual
Operating Instructions
ac 452.000 ft
O
N
O
F
F
Short
O
F
F
O
F
F
Figure 1–12: 455-ft Cable
A “rise” or “fall” is a signature of an impedance mismatch (fault). A dramatic rise
in the pulse indicates and open. A dramatic lowering of the pulse indicates a short.
Variations, such as inductive and capacitive effects on the cable, will appears as
bumps and dips in the waveform. Capacitive faults appear as a lowering of the pulse
(e.g., water in the cable). Inductive faults appear as a rising of the pulse (e.g., fray).
Whenever an abnormality is found, set the cursor at the beginning of the fault and
read the distance to the fault on the distance window of the LCD.
Reflection Coefficient
Measurements
The reflection coefficient is a measure of the impedance change at a point in the
cable. It is the ratio of the signal reflected back from a point, divided by the signal
going into that point. It is designated by the Greek letter r and is written in this
manual as rho. The 1502C measures the reflection coefficient in millirho
(thousandths of a rho).
To measure a reflection, adjust VERT SCALE to make the reflection one division
high. Read the reflection coefficient directly off the display above the VERT
SCALE control. For reflections that are greater than 500 mr/div, adjust VERT
SCALE for a reflection that is two divisions high and multiply the VERT SCALE
reading by two.
ac 0.000 ft
O
N
O
F
F
O
F
F
O
F
F
1502C MTDR Service Manual
Figure 1–13: Reflection Adjusted to One Division in Height
1–15
Operating Instructions
In an ideal transmission system with no changes in impedance, there will be no
reflections, so rho is equal to zero. A good cable that is terminated in its
characteristic impedance is close to ideal and will appear as a flat line on the 1502C
display.
Small impedance changes, like those from a connector, might have reflections from
10 to 100 mr. If rho is positive, it indicates an impedance higher than that of the
cable before the reflection. It will show as an upward shift or bump on the waveform.
If rho is negative, it indicates an impedance lower than that of the cable prior to the
reflection. It will show as a downward shift or dip on the waveform.
If the cable has an open or short, all the energy sent out by the 1502C will be
reflected. This is a reflection coefficient of rho = 1, or +1000 mr for the open and
–1000 mr for the short.
Long cables have enough loss to affect the size of reflections. In the 1502C, this loss
will usually be apparent as an upward ramping of the waveform along the length of
the cable. In some cases, the reflection coefficient measurement can be corrected for
this loss. This correction can be made using a procedure very similar to the Vertical
Compensation for Higher Impedance Cable procedure (see the VERT SET REF
section).
Return Loss
Measurements
Return loss is another was of measuring impedance changes in a cable.
Mathematically, return loss is related to rho by the formula:
Return Loss (in dB) = –20 * log (base ten) of Absolute Value of Rho (V
ref/Vinc)
The 1502C can be made to display in dB instead of mr/div through the menu:
1. Press MENU.
2. Select Setup Menu.
3. Press MENU again.
4. Select Vertical Scale is: Millirho.
5. Press MENU again. This should change is to Vertical Scale is: Decibels.
6. Press MENU twice to return to normal operation.
To measure return loss with the 1502C, adjust the height of the reflected pulse to
be two divisions high and read the dB return loss directly off the LCD. The incident
pulse is set to be two divisions high at zero dB automatically when the instrument
is turned on.
1–16
1502C MTDR Service Manual
Operating Instructions
ac 0.000 ft
O
N
O
F
F
O
F
F
O
F
F
Figure 1–14: Return Loss
A large return loss means that most of the pulse energy was lost instead of being
returned as a reflection. The lost energy might have been sent down the cable or
absorbed by a terminator or load on the cable. A terminator matched to the cable
would absorb most of the pulse, so its return loss would be large. An open or short
would reflect all the energy, so its return loss would be zero.
Ohms-at-Cursor
The 1502C can compute and display what impedance mismatch would cause a
reflection as high (or low) as the point at the cursor. This measurement is useful for
evaluating the first impedance mismatch (first reflection) or small impedance
changes along the cable (e.g., connectors, splices).
This function can be selected in the Setup Menu. Once it is enabled, the impedance
value will be displayed under the distance in the distance window.
ac
O
N
O
F
F
O
F
F
O
F
F
2.800 ft
50.0 W
Ohms-at-Cursor
Readout
Figure 1–15: Ohms-at-Cursor
The accuracy of the difference measurement in impedance between two points near
each other is much better than the absolute accuracy of any single point
measurement. For example, a cable might vary from 51.3 W to 58.4 W across a
connector – the 7.1 W difference is accurate to about 2%. The 51.3 W measurement
by itself is only specified to be accurate to 10%.
1502C MTDR Service Manual
1–17
Operating Instructions
The series resistance of the cable to the point at the cursor affects the accuracy of
the impedance measurement directly . In a cable with no large impedance changes,
the series resistance is added to the reading. For example, the near end of a long 50 W
coaxial cable might read 51.5 W, but increase to 57.5 W several hundred feet along
the cable. The 6 W difference is due to the series resistance of the cable, not to a
change in the actual impedance of the cable.
Another limitation to the ohms-at-cursor function is that energy is lost going both
directions through a fault. This will cause readings of points farther down the cable
to be less accurate than points nearer to the instrument.
In general, it is not wise to try to make absolute measurements past faults because
the larger the fault, the less accurate those measurements will be. Although they do
not appear as faults, resistive pads (often used to match cable impedances) also
affect measurements this way.
Using VIEW INPUT
How to Store the
Waveform
When pushed, the VIEW INPUT button displays the input at the front panel CABLE
connector. When VIEW INPUT is turned off and no other buttons are pushed, the
display will not have a waveform on it (see Figure 1–16). The default condition
when the instrument is powered up is to have VIEW INPUT on.
ac 0.000 ft
O
F
F
O
F
F
O
F
F
O
F
F
Figure 1–16: Display with VIEW INPUT Turned Off
When pushed, the STORE button puts the current waveform being displayed into
memory. If already stored, pushing STORE again will erase the stored waveform.
The front panel control settings and the menu-accessed settings are also stored. They
are accessed under View Stored Waveform Settings in the first level of the menu.
1–18
1502C MTDR Service Manual
ac 3.000 ft
O
N
O
F
F
O
F
F
O
N
Figure 1–17: Display of a Stored Waveform
Operating Instructions
Using VIEW STORE
Using VIEW DIFF
The VIEW STORE button, when pushed on, displays the waveform stored in the
memory as a dotted line. If there is no waveform in memory , a message appears on
the LCD informing you of this.
ac 3.000 ft
O
F
F
O
N
O
F
F
O
N
Figure 1–18: Display of a Stored Waveform
When pushed on, the VIEW DIFF button displays the difference between the current
waveform and the stored waveform as a dotted line. If no waveform has been stored,
a message will appear. The difference waveform is made by subtracting each point
in the stored waveform from each point in the current waveform.
1502C MTDR Service Manual
NOTE. If the two waveforms are identical (e.g., if ST ORE is pushed and VIEW DIFF
is immediately pushed) the difference would be zero. Therefore you would see the
difference waveform as a straight line.
The VIEW DIFF waveform will move up and down with the current input as you
move the
n
POSITION control. Any of the waveforms may be turned on or off
o
independently . You might want to turn off some waveforms if the display becomes
too busy or confusing.
1–19
Operating Instructions
NOTE. Because the stored waveform is not affected by changes in the instrument
controls, care should be taken with current waveform settings or the results could
be misleading.
One method to minimize the overlapping of the waveforms in VIEW DIFF is:
1. Move the waveform to be stored into the top half of the display.
ac 3.000 ft
O
N
O
F
F
O
F
F
O
N
Figure 1–19: Waveform Moved to Top Half of Display
2. Push STORE to capture the waveform. Remember, once it is stored, this
waveform cannot be moved on the display.
3. Move the current waveform (the one you want to compare against the stored
waveform) to the center of the display.
4. Push VIEW STORE and the stored waveform will appear above the current
waveform.
ac 3.000 ft
O
N
O
N
O
F
F
O
N
Figure 1–20: Current Waveform Centered, Stored W aveform Above
1–20
5. Push VIEW DIFF and the difference waveform will appear below the current
waveform.
1502C MTDR Service Manual
Operating Instructions
n
o
ac 3.000 ft
O
N
O
N
O
N
O
N
Stored Waveform
VIEW STORE
Current Waveform
VIEW INPUT
Difference
VIEW DIFF
Figure 1–21: Current Waveform Center , Stored W aveform Above, Difference Below
Notice the VIEW INPUT waveform is solid, VIEW DIFF is dotted, and VIEW
STORE is dot-dash.
There are many situations where the VIEW DIFF function can be useful. One
common situation is to store the waveform of a suspect cable, repair the cable, then
compare the two waveforms after the repair. During repairs, the VIEW INPUT,
VIEW DIFF , and VIEW ST ORE waveforms can be used to judge the effectiveness
of the repairs. The optional chart recorder can be used to make a chart of the three
waveforms to document the repair.
Another valuable use for the VIEW DIFF function is for verifying cable integrity
before and after servicing or periodic maintenance that requires moving or
disconnecting the cable.
The VIEW DIFF function is useful when you want to see any changes in the cable.
In some systems, there might be several reflections coming back from each branch
of the network. It might become necessary to disconnect branch lines from the cable
under test to determine whether a waveform represents a physical fault or is simply
an echo from one of the branches. The STORE and VIEW DIFF functions allow you
to see and compare the network with and without branches.
Two important things to be observed when using the VIEW DIFF function:
H If you change either the VERT SCALE or DIST/DIV, you will no longer be
comparing features that are the same distance apart or of the same magnitude
on the display. It is possible to save a feature (e.g., a connector or tap) at one
distance down the cable and compare it to a similar feature at a different distance
by moving the
POSITION and
n
POSITION controls.
o
H When this is done, great care should be taken to make sure the vertical and
horizontal scales are identical for the two waveforms being compared. If either
the stored or current waveform is clipped at the top or bottom of the display , the
difference waveform will be affected.
1502C MTDR Service Manual
1–21
Operating Instructions
n
o
Using Horizontal Set
Reference
HORZ SET REF (D mode) allows you to offset the distance reading. For example,
a lead-in cable to a switching network is three feet long and you desire to start the
measurement after the end of the lead-in cable. HORZ SET REF makes it simple.
ac 0.000 ft
O
N
O
F
F
O
F
F
O
F
F
End of
3-ft cable
Figure 1–22: Waveform of Three-Foot Lead-in Cable
1. Turn the NOISE FIL TER control to HORZ SET REF. The noise readout on the
LCD will show: set D.
2. Turn the
POSITION control to set the cursor where you want to start the
distance reading. This will be the new zero reference point. For a three-foot
lead-in cable, the cursor should be set at 3.00 ft.
ac 3.000 ft
O
N
O
F
F
O
F
F
O
F
F
move cursor to reference and Press STORE
Figure 1–23: Cursor Moved to End of Three-Foot Lead-in Cable
3. Push STORE.
4. Turn the NOISE FIL TER control to 1 avg. The instrument is now in HORZ SET
REF , or delta mode. The distance window should now read 0.00 ft. As the cursor
is scrolled down the cable, the distance reading will now be from the new zero
reference point.
1–22
1502C MTDR Service Manual
Operating Instructions
n
o
ac
O
N
O
F
F
O
F
F
O
F
F
0.000 ft
D
Figure 1–24: Cursor Moved to End of Three-Foot Lead-in Cable
NOTE. Vp changes will affect where the r eference is set on the cable. Be sure to set
the Vp first, then set the delta to the desired location.
5. To exit HORZ SET REF, use the following procedure:
a. Turn the NOISE FILTER control to HORZ SET REF.
b. Turn DIST/DIV to .1 ft/div. If the distance reading is extremely high, you
might want to use a higher setting initially , then turn to .1 ft/div for the next
adjustment.
Using Vertical Set
Reference
c. Turn the
POSITION control until the distance window reads 0.00 ft.
ac 0.000 ft
O
N
O
F
F
O
F
F
O
F
F
move cursor to reference and Press STORE
Figure 1–25: Cursor Moved to 0.00 ft
d. Push STORE.
e. Turn NOISE FILTER to desired setting.
VERT SET REF works similar to HORZ SET REF except that it sets a reference
for gain (pulse height) instead of distance. This feature allows zeroing the dB scale
at whatever pulse height is desired.
1. Turn NOISE FIL TER fully counterclockwise. “Set Ref” will appear in the noise
averaging area of the LCD.
1502C MTDR Service Manual
1–23
Operating Instructions
n
o
2. Adjust the incident pulse to the desired height (e.g., four divisions). It might be
necessary to adjust
ac 0.000 ft
O
N
O
F
F
O
F
F
O
F
F
set vertical scale and press STORE
n
POSITION.
o
Figure 1–26: Incident Pulse at Three Divisions
3. Push STORE.
4. Return NOISE FILTER to the desired setting. Notice that the vertical scale now
reads 500 mr/div.
NOTE. The millirho vertical scale will not be in calibration after arbitrarily
adjusting the pulse height.
Vertical Compensation for
Higher Impedance Cable
The millirho scale is the reciprocal of the number of divisions high the pulse has
been set. For example, 1 pulse divided by 4 divisions equals 0.25 or 250 mr/div.
When testing cables other than 50 W, this procedure allows reflection measurements
in millirho.
1. Attach a short sample of the given cable (75 W in this example)to the
instrument.
ac 19.200 ft
O
N
O
F
F
O
F
F
O
F
F
Figure 1–27: Waveform of Short 75 W Cable
2. Adjust the
POSITION control to position the reflected pulse at center screen.
1–24
1502C MTDR Service Manual
Operating Instructions
n
o
3. Turn NOISE FILTER to VERT SET REF.
4. Adjust VERT SCALE so the reflected pulse (from open at far end of cable
sample) is two divisions high.
ac 19.200 ft
O
N
O
F
F
O
F
F
O
F
F
set vertical scale and press STORE
Figure 1–28: Waveform Centered and Adjusted Vertically
5. Press STORE.
6. Return NOISE FILTER to the desired setting.
7. Adjust the
POSITION control to the desired position on the waveform to
measure loss.
ac 1.840 ft
O
N
O
F
F
O
F
F
O
F
F
Figure 1–29: Cursor Moved to Desired Position
The instrument is now set to measure reflections in millirho relative to the sample
cable impedance.
To measure reflections on a 50 W cable, the VERT SET REF must be reset.
8. To exit VERT SET REF, use the following procedure:
a. Turn NOISE FILTER to VERT SET REF.
b. Adjust VERT SCALE to obtain an incident pulse height of two divisions.
c. Push STORE.
1502C MTDR Service Manual
1–25
Operating Instructions
d. Turn NOISE FILTER to desire filter setting.
The instrument can be turned off and back on to default to the two division pulse
height.
Additional Features (Menu Selected)
Max Hold
The 1502C will capture and store waveforms on an ongoing basis. This is useful
when the cable or wire is subjected to intermittent or periodic conditions. The 1502C
will monitor the line and display any fluctuations on the LCD.
1. Attach the cable to the 1502C front-panel CABLE connector.
2. Push MENU to access the main menu.
3. Scroll to Setup Menu and push MENU again.
4. Scroll to Acquisition Control Menu and push MENU again.
5. Scroll to Max Hold is: Off and push MENU again. This line will change to Max
Hold is: On. The monitoring function is now ready to activate.
6. Repeatedly push MENU until the instrument returns to normal operation.
ac 0.000 ft
O
N
1–26
O
F
F
Figure 1–30: Waveform Viewed in Normal Operation
7. When you are ready to monitor this cable for intermittents, push STORE. The
1502C will now capture any changes in the cable.
1502C MTDR Service Manual
Operating Instructions
ac 0.000 ft
O
N
Captured
changes
O
N
Figure 1–31: Waveform Showing Intermittent Changes
8. To exit monitor mode, push STORE again.
9. To exit Max Hold, access the Acquisition Control Menu again, turn off Max
Hold, and push MENU repeatedly until the instrument returns to normal
operation.
Pulse On/Off
This feature puts the 1502C in a “listening mode” by turning off the pulse generator .
1. Attach a cable to the 1502C front-panel CABLE connector.
2. Push MENU to access the Main Menu.
3. Scroll to Setup Menu and push MENU again.
4. Scroll to Acquisition Control Menu and push MENU again.
5. Scroll to Pulse is: On and push MENU again. This will change to Pulse is: Off.
ac 0.000 ft
O
N
O
F
F
O
F
F
O
F
F
Figure 1–32: Waveform Display with No Outgoing Pulses
1502C MTDR Service Manual
6. Repeatedly press MENU until the instrument returns to normal operation.
1–27
Operating Instructions
CAUTION. This function is used mostly for troubleshooting by qualified technicians.
It is not recommended that you use the 1502C as a stand-alone monitoring device.
The input circuitry is very sensitive and can be easily damaged by even moderate
level signals.
NOTE. In this mode, the 1502C is acting as a detector only. Any pulses detected will
not originate from the instrument, so any distance readings will be invalid. If you
are listening to a local ar ea network, for example, it is possible to detect traffic, but
not possible to measure the distance to its origin.
Pulse is: Off can be used in conjunction with Max Hold is: On.
7. To exit Pulse is: Off, access the Acquisition Control Menu again, turn pulse back
on, then push MENU until the instrument returns to normal operation.
Single Sweep
The single sweep function will acquire one waveform only and display it.
1. Attach a cable to the 1502C front-panel CABLE connector.
2. Push MENU to access the Main Menu.
3. Scroll to Setup Menu and push MENU again.
4. Scroll to Acquisition Control Menu and push MENU again.
5. Scroll to Single Sweep is: Off and push MENU again. This will change to Single
Sweep is: On.
6. Repeatedly press MENU until the instrument returns to normal operation.
7. When you are ready to begin a sweep, push VIEW INPUT. A sweep will also
be initiated when you change any of the front-panel controls. This allows you
to observe front panel changes without exiting the Single Sweep mode.
As in normal operation, averaged waveforms will take longer to acquire.
1–28
1502C MTDR Service Manual
Operating Instructions
ac 0.000 ft
O
F
F
O
F
F
O
F
F
O
F
F
Figure 1–33: A Captured Single Sweep
8. To exit Single Sweep is: On, access the Acquisition Control Menu again, turn
the Single Sweep back off, then repeatedly push MENU until the instrument
returns to normal operation.
1502C MTDR Service Manual
1–29
Operating Instructions
1–30
1502C MTDR Service Manual
Operator Performance Checks
This chapter contains performance checks for many of the functions of the 1502C.
They are recommended for incoming inspections to verify that the instrument is
functioning properly . Procedures to verify the actual performance requirements are
provided in chapter 6.
Performing these checks will assure you that your instrument is in good working
condition. These checks should be performed upon receipt of a new instrument or
one that has been serviced or repaired. It does not test all portions of the instrument
to Calibration specifications.
The purpose of these checks is not to familiarize a new operator with the instrument.
If you are not experienced with the instrument, you should read the Operating
Instructions chapter of this manual before going on with these checks.
If the instrument fails any of these checks, it should be serviced. Many failure modes
affect only some of the instrument functions.
Equipment Required
Item Tektronix Part Number
50 W precision terminator 011–0123–00
3-foot precision coaxial cable 012–1350–00
Getting Ready
Power On
Metric Instruments
1502C MTDR Service Manual
Disconnect any cables from the front-panel CABLE connector. Connect the
instrument to a suitable power source (a fully charged optional battery pack or AC
line source). If you are using AC power, make sure the fuse and power switch are
correct for the voltage you are using (115 VAC requires a different fuse than
230 VAC).
Pull the POWER switch on the front panel. If a message does not appear on the
display within a second or two, turn the instrument off. There are some failure modes
that could permanently damage or ruin the LCD if the power is left on for more than
a minute or so.
Option 05 instruments default to metric; however, you can change the metric scale
to ft/div in the Setup Menu or use the metric numbers provided. To change the
readings, press the MENU button. Using the
Setup Menu and press MENU again. Scroll down to Distance/Div is: m/div and press
MENU again. This will change to ft/div. Press the MENU button repeatedly to
return to normal operation mode. If the instrument power is turned off, these checks
must be repeated again when the instrument is powered on again.
n
POSITION control, scroll down to
o
2–1
Operator Performance Checks
Set Up
1. Horizontal Scale
(Timebase) Check
Set the 1502C front-panel controls:
NOISE FILTER 1 avg
VERT SCALE default
DIST/DIV 1 ft/div (0.25 m)
Vp .66
If the instrument fails this check, it must be repaired before any distance
measurements can be made with it.
1. Turn the 1502C power on. The display should look very similar to Figure B–1.
ac 0.000 ft
O
N
O
F
F
O
F
F
O
F
F
Figure 2–1: Start-up Measurement Display
2. Connect the 3-foot precision cable to the front-panel CABLE connector. The
display should now look like Figure B–2.
ac 0.000 ft
O
N
O
F
F
O
F
F
O
F
F
Figure 2–2: Measurement Display with 3-foot Cable
n
3. Using the
o
POSITION control, measure the distance to the rising edge of the
waveform at the open end of the cable. The distance shown on the display
distance window (upper right corner of the LCD) should be from 2.87 to 3.13
feet (0.875 to 0.954 m).
2–2
1502C MTDR Service Manual
Operator Performance Checks
ac 3.000 ft
O
N
O
F
F
O
F
F
O
F
F
Figure 2–3: Cursor at End of 3-foot Cable
4. Remove the 3-foot cable and connect the 50 W terminator.
5. Change the DIST/DIV to 200 ft/div (50 m/div)
n
o
6. Turn the
POSITION control clockwise until the distance window shows a
distance greater than 2,000 feet (> 600 m). The waveform should be a flat line
from the pulse to this point.
ac 2051.000 ft
O
N
O
F
F
O
F
F
O
F
F
Figure 2–4: Flat-Line Display Out to 50,000+ Feet
n
7. Turn the
o
POSITION control counterclockwise until the distance window
shows a distance less than 10.000 feet (< 3.1 m).
8. Set the DIST/DIV control to .1 ft/div (0.025 m/div).
1502C MTDR Service Manual
n
9. Turn the
o
POSITION control counterclockwise until the distance window
shows a distance of –2.000 feet (–0.611 m).
2–3
Operator Performance Checks
ac –2.000 ft
O
N
O
F
F
O
F
F
O
F
F
Figure 2–5: Flat-Line Display at –2.000 ft
This last step has set up the instrument for the next check.
2. Vertical Position
(Offset) Check
If the instrument fails this test, it can be used, but should be serviced when possible.
Not all of the waveforms will be viewable at all gain settings.
1. Using the
n
POSITION control, verify that the entire waveform can be moved
o
to the very top of the display (off the graticule area).
ac –2.000 ft
Waveform
O
N
O
F
F
O
F
F
O
F
F
off display
Figure 2–6: Waveform Off the Top of the Display
n
2. Using the
POSITION control, verify that the entire waveform can be moved
o
to the very bottom of the display (to the bottom graticule line).
2–4
1502C MTDR Service Manual
ac –2.000 ft
O
N
O
F
F
O
F
F
O
F
F
Figure 2–7: Waveform at the Bottom of the Display
Operator Performance Checks
Waveform
3. Noise Check
If the instrument fails this check, it can still be usable for measurements of large
faults that do not require a lot of gain, but send the instrument to be serviced when
possible. A great deal of noise reduction can be made using the NOISE FILTER
control.
n
1. Adjust the
o
POSITION control to obtain 100.000 ft in the distance window .
ac 100.000 ft
O
N
O
F
F
O
F
F
O
F
F
Figure 2–8: Waveform with Gain at 5.00 mr/div
n
2. Using the
POSITION control and VER T SCALE control, set the gain to 5.00
o
mr/div. Keep the waveform centered vertically in the display.
3. Press MENU.
1502C MTDR Service Manual
n
4. Using the
POSITION control, select Diagnostics Menu.
o
5. Press MENU again.
n
6. Using the
POSITION control, select Service Diagnostic Menu.
o
7. Press MENU again.
n
8. Using the
POSITION control, select Noise Diagnostics.
o
9. Press MENU again and follow the instructions on the display.
2–5
Operator Performance Checks
10. Exit from Noise Diagnostics, but do not exit from the Service Diagnostic Menu
yet.
4. Offset/Gain Check
5. Sampling Efficiency
Check
If the instrument fails this check, it should not be used for loss or impedance
measurements. Send it to be serviced when possible.
1. In the Service Diagnostic Menu, select the Offset/Gain Diagnostic and follow
the directions on the display.
NOTE. Occasionally, the instrument might not pass the 48 dB step. This is no cause
for alarm. If the remainder of the steps do not fail, pr oceed as normal. Refer to the
1502C Service Manual for additional information.
There are three screens of data presented in this diagnostic. The Pass/Fail level is
3% for any single gain setting tested.
2. Exit from Offset/Gain Diagnostic, but do not leave the Service Diagnostic
Menu yet.
If the instrument fails this check, the waveforms might not look normal. If the
efficiency is more than 100%, the waveforms will appear noisy . If the efficiency is
below the lower limit, the waveform will take longer (more pixels) to move from
the bottom to the top of the reflected pulse. This smoothing effect might completely
hide some faults that would normally only be one or two pixels wide on the display .
6. Aberrations Check
2–6
1. In the Service Diagnostic Menu, select Sampling Efficiency and follow the
directions on the screen.
2. When done with the test, press the MENU button repeatedly until the instrument
returns to normal operation.
If the aberrations are out of specification, the ohms-at-cursor function might be less
accurate than specified.
1. Connect the 50 W precision terminator to the front-panel CABLE connector.
2. Set the DIST/DIV control to 5 ft/div (1 m/div).
3. Increase the VERT SCALE control to 50 mr/div.
4. Using the
n
POSITION control, move the top of the pulse to the center graticule
o
line.
1502C MTDR Service Manual
Operator Performance Checks
ac –2.000 ft
O
N
O
F
F
O
F
F
O
F
F
Figure 2–9: Top of Pulse on Center Graticule
5. Set the DIST/DIV control to 0.2 ft/div (0.05 m/div).
n
o
6. Turn the
POSITION control clockwise until the rising edge of the incident
pulse is in the left-most major division on the display.
ac 1.160 ft
O
N
O
F
F
O
F
F
O
F
F
Figure 2–10: Rising Edge of Incident Pulse in Left-most Major Division
n
o
7. Using the
POSITION control, move the cursor back to 0.000 ft (0.00 m).
All the aberrations, except the one under the cursor (see Figure 2–11), must be
within one division of the center graticule line from out to 10 feet past the rising
edge of the pulse.
T o verify distances past the right edge of the display , scroll along the waveform
by turning the
n
o
POSITION control clockwise.
1502C MTDR Service Manual
2–7
Operator Performance Checks
ac 0.000 ft
O
N
O
F
F
O
F
F
O
F
F
Figure 2–11: Waveform Centered, Cursor at 0.000 ft
7. Risetime Check
If the risetime is out of specification, it might be difficult to make accurate
short-distance measurements near the front panel.
1. Set the 1502C front-panel controls:
NOISE FILTER 1 avg
VERT SCALE 500 mr/div
DIST/DIV 0.2 ft/div (0.05 m)
Vp .99
n
o
2. Using the
POSITION control, move the incident pulse to the center of the
display as shown below.
ac –1.432 ft
O
N
O
F
F
O
F
F
O
F
F
2–8
Figure 2–12: Pulse Centered on Display
3. Turn the VERT SCALE control clockwise until the leading edge of the incident
pulse is five major divisions high (about 205 mr).
4. Position the waveform so that it is centered about the middle graticule line.
1502C MTDR Service Manual
ac –0.848 ft
O
N
O
F
F
Operator Performance Checks
O
F
F
O
F
F
Crosses
Lowest
Point
Figure 2–13: Cursor on Lowest Major Graticule that Rising Edge Crosses
n
5. Using the
o
POSITION control, and noting the distances displayed, verify that
the distance between the points where the leading edge crosses the highest and
lowest major graticule lines is less than or equal to 0.096 feet (0.029 m).
ac –0.768 ft
O
N
Crosses
Highest
Point
O
F
F
O
F
F
O
F
F
8. Jitter Check
1502C MTDR Service Manual
Figure 2–14: Cursor on Highest Major Graticule that Rising Edge Crosses
In the above example, the distances are –0.848 feet and –0.768 feet. The difference
between these two measurements is 0.080 feet, which is well within specification.
Jitter is the uncertainty in the timebase. Its main effect is that the waveform appears
to move back and forth a very small amount. If the jitter is too great, it will affect
the repeatability of very precise distance measurements.
1. Set the VERT SCALE less than or equal to 1.0 mr/div.
2. Watch the leading edge of the pulse move and verify that this movement is less
than five pixels, or < 0.02 ft (0.006 m).
2–9
Operator Performance Checks
ac –1.624 ft
O
N
O
F
F
O
F
F
O
F
F
Jitter
Figure 2–15: Jitter Apparent on Leading Edge of Incident Pulse
Using the Max Hold function (accessed in the Setup Menu, Acquisition Control) can
simplify your observation of jitter. Max Hold allows you to observe the accumulated
jitter without having to stare continuously at the display.
ac –1.624 ft
Conclusions
O
N
O
F
F
Accumulated
Jitter
O
F
F
O
F
F
Figure 2–16: Jitter Captured Using Max Hold
If the instrument failed Jitter or Risetime checks, it is probably still adequate for all
but extremely precise distance measurements. If it failed the Horizontal Scale check,
you should not use the instrument until the cause of the failure has been identified
and corrected.
All of the previous checks only test the major functional blocks of the instrument
that could prevent you from being able to make measurements. It is possible for the
front-panel controls or the LCD to have problems that would interfere with
controlling or displaying measurements. Most problems of this type would become
evident as you perform the checks. If you suspect a problem of this nature, you
should have the instrument checked by a qualified service technician, using the
diagnostics in the 1502C Service Manual.
2–10
If the instrument passed all of the previous checks, it is ready for use.
1502C MTDR Service Manual
Specifications
The tables in this chapter list the characteristics and features that apply to this
instrument after it has had a warm-up period of at least five minutes.
The Performance Requirement column describes the limits of the Characteristic.
Supplemental Information describes features and typical values or other helpful
information.
Electrical Characteristics
Characteristic Performance Requirement Supplemental Information
Excitation Pulse
Reflected Pulse
Aberrations
Jitter
Output Impedance 50 W nominal
Pulse Amplitude 300 mV nominal into 50 W load
Pulse Width 25 ms nominal
Pulse Repetition Time 200 ms nominal
Vertical
Scales
Accuracy
v200 ps (0.096 feet)
"5% peak within 0 to 10 feet after rise
"0.5% peak beyond 10 feet
v0.02 feet (v40 ps) p-p Horz scale 0.1 ft/div
v0.2 feet (v400 ps) p-p Horz scale 1 ft/div
0.5 mr/div to 500 mr/div,
Within "3% of full scale
Vp set to 0.99; 10 to 90%, into a precision short
Excluding front panel BNC
Vp set to 0.99, DIST/DIV set to 0.1 ft/div
At 23.4 feet to 46.8 feet, jitter is v0.4 feet.
While pulse is on, typically "2%
> 240 values, includes 1, 2, 5 sequences
(accuracy depends on reference level)
Set Adj
Vertical Position Any waveform point is moveable to center screen
Displayed Noise
Distance Cursor
Resolution
Cursor Readout
Range
Resolution
Distance Measurement
Accuracy
"5 mr peak or less, filter set to 1
"2 mr peak or less, filter set to 8
1.6 inches or "1% of distance measured,
whichever is greater
Set incident pulse within 3%. Combined with
VERT SCALE control.
1/25th of 1 major division
–2 ft to w2,000 ft
0.004 ft
For cables with Vp = 0.66
For delta mode measurements
Error v0.5% for distance w27 ft
Error v1.0% for distance w14 ft
Error v2.0% for distance w7 ft
Error v10% for distance w1.5 ft
(continued next page)
1502C MTDR Service Manual
3–1
Specifications
Characteristic Performance Requirement Supplemental Information
Cursor Ohms Readout
Range
1 W to 1 kW
Resolution
Accuracy
Horizontal
Scales
Range
Horizontal Position Any distance to full scale can be moved on
Vp
Range
Resolution
Accuracy
Custom Option Port Tektronix Chart Recorders YT–1 and YT–1S are
Line Voltage 115 VAC (90 to 132 V AC) 45 to 440 Hz, or
Battery
Operation
Within "1%
230 VAC (180 to 250 VAC) 45 to 440 Hz, or
12 VDC through battery pack connector
5 hours minimum, 20 chart recordings maximum
3 significant digits
"10% with serial cable impedance
correction (relative impedance
measurements "2%)
0.1 ft/div to 200 ft/div (0.025 m/div to 50 m/div)
11 values, 1, 2, 5 sequence
1 ft to 2,000 ft (2.5 m to 500 m)
screen
Propagation velocity relative to air
0.30 to 0.99
0.01
designed to operate with the 1502C. Produces a
high resolution thermal dot matrix recording of
waveform and switch values.
Fused at 0.3 A (0.3 A, 250 V , T)
Fused at 0.15 A (0.15 A, 250 V , T)
+15° C to +25° C charge and discharge temp,
LCD backlight off. Operation of instrument with
backlight on or at temps below +10° C will
degrade battery operation specification
Full Charge Time
Overcharge Protection
Discharge Protection
Charge Capacity
Charge Indicator
3–2
20 hours maximum
Limited to 10 days continuous charge. Battery
will charge whenever instrument is plugged in.
Battery can be removed during AC operation.
Operation terminates prior to cell reversal
2 Amp-hours typical
Bat/low will be indicated on LCD when capacity
reaches approximately 10%
1502C MTDR Service Manual
Environmental Characteristics
Characteristic Performance Requirement Supplemental Information
Temperature
Operating
–10° C to +55° C
Specifications
Battery capacity reduced at other than +15°C to
+25°C
Non-operating
Humidity to 100%
Altitude
Operating
Non-operating
Vibration 5 to 15 Hz, 0.06 inch p–p
Shock, Mechanical
Pulse
Bench Handling
Operating
Non-operating
Loose Cargo Bounce 1 inch double-amplitude orbital path at 5 Hz,
Water Resistance
Operating
–62° C to +85° C
to 10,000 ft
to 40,000 ft
15 to 25 Hz, 0.04 inch p–p
25 to 55 Hz, 0.013 inch p–p
30 g, 11 ms 1/2 sine wave, total of 18 shocks
4 drops each face at 4 inches or 45 degrees
with opposite edge as pivot
4 drops each face at 4 inches or 45 degrees
with opposite edge as pivot. Satisfactory operation after drops.
6 faces
Splash-proof and drip-proof
With battery removed. Storage temp with battery in is –20° C to +55° C. Contents on non-
volatile memory (stored waveform) might be lost
at temps below –40° C.
MIL–T–28800C, Class 3
MIL–T–28800C, Class 3
MIL–T–28800C, Class 3
MIL–STD–810, Method 516, Procedure V
Cabinet on, front cover off
Cabinet off, front cover off
MIL–STD–810, Method 514, Procedure XI,
Part 2
MIL–T–28800C, Style A
Front cover off
Non-operating
Salt Atmosphere Withstand 48 hours, 20% solution without
Sand and Dust Operates after test with cover on, non-operating MIL–STD–810, Method 510, Procedure I
Washability Capable of being washed
Fungus Inert Materials are fungus inert
Watertight with 3 feet of water above top of case
corrosion
Front cover on
(continued next page)
1502C MTDR Service Manual
3–3
Specifications
Certifications and Compliances
Category Standard or description
EC Declaration of Conformity –
EMC
Australia/New Zealand
Declaration of Conformity – EMC
EMC Compliance Meets the intent of Directive 89/336/EEC for Electromagnetic Compatibility when it is used with the
FCC Compliance Emissions comply with FCC Code of Federal Regulations 47, Part 15, Subpart B, Class A Limits.
Safety Standards
U.S. Nationally Recognized
Testing Laboratory Listing
Canadian Certification CAN/CSA C22.2 No. 231 CSA safety requirements for electrical and electronic measuring and
European Union Compliance Low Voltage Directive 73/23/EEC, amended by 93/68/EEC
Meets intent of Directive 89/336/EEC for Electromagnetic Compatibility . Compliance was demonstrated
to the following specifications as listed in the Official Journal of the European Union:
EN 50081-1 Emissions:
EN 55022 Class B Radiated and Conducted Emissions
EN 60555-2 AC Power Line Harmonic Emissions
EN 50082-1 Immunity:
IEC 801-2 Electrostatic Discharge Immunity
IEC 801-3 RF Electromagnetic Field Immunity
IEC 801-4 Electrical Fast Transient/Burst Immunity
IEC 801-5 Power Line Surge Immunity
Complies with EMC provision of Radiocommunications Act per the following standard(s):
AS/NZS 2064.1/2 Industrial, Scientific, and Medical Equipment: 1992
product(s) stated in the specifications table. Refer to the EMC specification published for the stated
products. May not meet the intent of the directive if used with other products.
UL1244 Standard for electrical and electronic measuring and test equipment.
test equipment.
EN 61010-1/A2 Safety requirements for electrical equipment for measurement,
control, and laboratory use.
Additional Compliance IEC61010-1/A2 Safety requirements for electrical equipment for measurement,
control, and laboratory use.
Safety Certification Compliance
Equipment Type Test and measuring
Safety Class Class 1 (as defined in IEC 61010-1, Annex H) – grounded product
Overvoltage Category Overvoltage Category II (as defined in IEC 61010-1, Annex J)
Pollution Degree Pollution Degree 3 (as defined in IEC 61010-1).
Installation (Overvoltage)
Category
Terminals on this product may have different installation (overvoltage) category designations. The
installation categories are:
CA T III Distribution-level mains (usually permanently connected). Equipment at this level is
typically in a fixed industrial location.
CA T II Local-level mains (wall sockets). Equipment at this level includes appliances, portable
tools, and similar products. Equipment is usually cord-connected.
CA T I Secondary (signal level) or battery operated circuits of electronic equipment.
(continued next page)
3–4
1502C MTDR Service Manual
Specifications
Category Standard or description
Pollution Degree A measure of the contaminates that could occur in the environment around and within a product.
Typically the internal environment inside a product is considered to be the same as the external. Products
should be used only in the environment for which they are rated.
Pollution Degree 1 No pollution or only dry , nonconductive pollution occurs. Products in this
category are generally encapsulated, hermetically sealed, or located in
clean rooms.
Pollution Degree 2 Normally only dry, nonconductive pollution occurs. Occasionally a
temporary conductivity that is caused by condensation must be
expected. This location is a typical office/home environment. Temporary
condensation occurs only when the product is out of service.
Pollution Degree 3 Conductive pollution, or dry, nonconductive pollution that becomes
conductive due to condensation. These are sheltered locations where
neither temperature nor humidity is controlled. The area is protected from
direct sunshine, rain, or direct wind.
Pollution Degree 4 Pollution that generates persistent conductivity through conductive dust,
rain, or snow. Typical outdoor locations.
Physical Characteristics
Characteristic Description
Weight
without cover
with cover
with cover, chart recorder, and battery pack
Shipping Weight
domestic
export
Height 5.0 inches (127 mm)
Width
with handle
without handle
Depth
with cover on
with handle extended to front
14.25 lbs (6.46 kg)
15.75 lbs (7.14 kg)
19.75 lbs (8.96 kg)
25.5 lbs (11.57 kg)
25.5 lbs (11.57 kg)
12.4 inches (315 mm)
11.8 inches (300 mm)
16.5 inches (436 mm)
18.7 inches (490 mm)
1502C MTDR Service Manual
3–5
Specifications
3–6
1502C MTDR Service Manual
Options and Accessories
The following options are available for the 1502C MTDR:
Option 04: YT–1 Chart Recorder
Option 04 instruments come equipped with a chart printer. Refer to the YT–1/ YT–1S
Chart Recorder Instruction Manual that comes with this option for instructions on
operation, paper replacement, and maintenance.
Option 05: Metric Default
Option 05 instruments will power up in the metric measurements mode. Standard
measurements may be selected from the menu, but metric will be the default.
Option 07: YT–1S Chart Recorder
Option 07 instruments come equipped with a splashproof chart printer. Refer to the
YT–1/ YT–1S Chart Recorder Instruction Manual that comes with this option for
instructions on operation, paper replacement, and maintenance.
Power Cord Options
1502C MTDR Service Manual
The following power cord options are available for the 1502C TDR. Note that these
options require inserting a 0.15 A fuse in the rear panel fuse holder.
NOTE. The only power cord rated for outdoor use is the standar d cord included with
the instrument (unless otherwise specified). All other optional power cords are
rated for indoor use only.
Option A1: 220 VAC, 16 A, Universal Europe
Option A2: 240 VAC, 13 A, United Kingdom
Option A3: 240 VAC, 10 A, Australia
Option A4: 240 VAC, 15A, North America
Option A5: 240 VAC, 6 A, Switzerland
4–1
Options and Accessories
Accessories
Standard Accessories
Part numbers for the following standard and optional accessories are listed at the end
of the Replaceable Mechanical Parts list.
Internal Lead–gel Battery Assembly
Replacement Fuse (AC line fuse, 115 VAC)
Replacement Fuse (AC line fuse, 230 VAC)
Power Cord (outdoor rated)
Option Port Cover Assembly
Optional Accessories
Precision 50 W Test Cable (S/N w
50 W BNC Terminator
BNC Connector, female-to-female
Slide Rule Calculator
Slide Application Note (bound in this manual)
Accessory Pouch
Operator Manual
Service Manual
Battery
Chart Recorder, YT–1S
Chart Paper, single roll
Chart Paper, 25-roll pack
Chart Paper, 100-roll pack
B021135)
4–2
Connector, BNC male to BNC male
Connector, BNC female to Alligator Clip (S/N wB025708)
Connector, BNC female to Hook-tip Leads
Connector, BNC female to Dual Banana Plug
Connector, BNC male to Dual Binding Post
1502C MTDR Service Manual
Connector, BNC male to N female
Connector, BNC female to N male
Connector, BNC female to UHF male
Connector, BNC female to UHF female
Connector, BNC female to Type F male
Connector, BNC male to Type F female
Connector, BNC female to GR
Connector, BNC male to GR
Terminator, 75 W BNC
Adapter, Direct Current
* Adapter, 50/75 W
Options and Accessories
* Adapter, 50/93 W
* Adapter, 50/125 W
* These adapters should be purchased if GR connectors (017–0063–00. . . .
and/or 017–0064–00) are purchased.
1502C MTDR Service Manual
4–3
Options and Accessories
4–4
1502C MTDR Service Manual
Circuit Descriptions
Introduction
This chapter describes how the instrument works. First is a circuit overview and how
it relates to the block diagram (Figure 5–1, next page). Following that are the
separate sections of the instrument, discussed in detail.
The 1502C uses time-domain reflectometry techniques to detect and display the
impedance characteristics of a metallic cable from one end of the cable. This is
accomplished by applying a rapidly rising step to the cable and monitoring the
resulting voltage over a period of time. If the cable has a known propagation
velocity , the time delay to a particular reflection can be interpreted in cable distance.
Amplitude of the reflected voltage is a function of the cable impedance and the
impedance of the termination relative to the cable leading to it. The amplitude can
be interpreted in rho or dB. Rho (r) is a convenient impedance function defined as
the voltage reflection coefficient. It is the ratio between the incident step and the
reflected step. For the simple case of a cable with a resistive load:
R
- Z
L
r =
Where:
is the load impedance, and
R
L
Z
is the characteristic impedance.
O
The 1502C instrument is comprised of several subsections, as shown in the block
diagram (Figure 5–1). These are organized as a processor system, which controls
several peripheral circuits to achieve overall instrument performance.
The processor system reads the front-panel control settings to determine the cable
information that you selected for viewing. Distance settings are converted to
equivalent time values and loaded into the timebase circuits.
The timebase generates repetitive strobe signals to trigger the driver/sampler
circuits. Pulse strobes cause a step to be applied to the cable under test. Sample
strobes causes a single sample of the cable voltage to be taken during a very short
interval. The timebase precisely controls the time delay of the sample strobe relative
to the pulse strobe. When many sequential samples are recombined, a replica of the
cable voltage is formed. This sampling technique allows extremely rapid repetitive
waveforms to be viewed in detail.
RL + Z
O
O
1502C MTDR Service Manual
5–1
Circuit Descriptions
Cable
Front Panel
Drivers LCD
Controls, LCD Bias
and temp. compensation
Digital Bus
Main Board
CPU
Z80
RAM
ROM
Front End
Driver Sampler
Hybrid
Timebase
Digital
Analog
Signal Processing
Decoding
Option Port
Power Supply
AC to DC
Converter
Figure 5–1: System Block Diagram
Offset Gain
A/D converter
Power Bus
Control
DC to DC
Converter
Battery
5–2
1502C MTDR Service Manual
Circuit Descriptions
Referring to the waveforms in Figure 5–2, cable voltage waveforms are shown at
the top. Each step is from the pulse generator and all steps are identical. At time
delays (t
, t
, t
n
n+1
, etc.) after the steps begin, a sample of the step amplitude is
n+2
taken. Each of these samples is digitized and stored in the processor until sufficient
points are accumulated to define the entire period of interest. The samples are then
processed and displayed at a much slower rate, forming the recombined waveform
as shown. This process allows the presentation of waveforms too rapidly to be
viewed directly.
Cable
voltage
tn tn+1 tn+2
Voltage
samples
Recombined
samples
Figure 5–2: Waveform Accumulation Diagram
Voltage samples from the driver/sampler are combined with a vertical position
voltage derived from the front-panel control, then amplified. The amplifier gain is
programmed by the processor to give the selected vertical sensitivity. Each
amplified sample voltage is then digitized by an analog-to-digital converter and
stored in the processor memory.
When the processor has accumulated sufficient samples (251) to form the desired
waveform, the samples are formatted. This formatted data is then transferred to the
display memory . The display logic routes the data to each pixel of the LCD, where
each digital data bit determines whether or not a particular pixel is turned on or off.
Between each waveform, samples are taken at the cursor location for the “ohms at
cursor” function, and at the leading edge of the incident step for use by the timebase
correction circuit.
Cursor and readout display data is determined by the processor and combined with
the formatted sample waveform before it is sent to the display.
1502C MTDR Service Manual
5–3
Circuit Descriptions
Power Supply
Introduction
115/230 volt
AC line
EMI
Line
Filter
The power supply consists of the following:
H Primary Circuit
H Pre-regulator
H Battery Charger
H Deep Discharge Protection
H Port-regulator
H DC-to-DC Converters
The power supply converts either 115/230 VAC line power, or takes power from a
lead-gel battery, and provides the instrument with regulated DC voltages. A block
diagram of the power supply is shown in Figure 5–3.
Instr.
Pwr.
Fuse and
Line Select
Switch
Battery
+ 12 VDC
Step down
XFMR
Rectifier
&
Filter Cap.
+ 30 VDC + 15.8 VDC
Switcher
&
Prereq.
Battery
Charger
Switch
+ 10 to 15.5 VDC
Transistor Power Switch + 16.2 VDC
Deep
Discharge
Protection
Switcher and
Post–regulator
DC to DC
Converter
+ 16 VDC
5 VDC
±
15 VDC
±
Figure 5–3: Power Supply Block Diagram
Single-phase AC line voltage is applied to the power supply module through a
power plug with internal EMI filter. The filtered line voltage is immediately fused,
routed through a line selector switch and applied to a stepdown transformer. The
transformer secondary voltage is rectified and power switched to power the post
regulator.
DC Power
to Instrument
Power
Status
5–4
1502C MTDR Service Manual
Circuit Descriptions
A switching pre-regulator reduces this voltage to +15.8 VDC and is used to power
the battery charger. This voltage is also processed through a rectifier and power
switch to power the post-regulator.
If a battery is installed, the battery charger operates as a current source to provide
a constant charging current. Voltage limiting circuits in the charger prevent battery
overcharge by reducing the charge current as the battery voltages approaches +12.5
VDC.
The battery provides a terminal voltage of 10 to 12.5 VDC, with a nominal capacity
of up to 2.0 Amp-Hours. It also is connected through a rectifier to the instrument’s
power switch and post-regulator.
When the power switch is closed, an FET power transistor is momentarily turned
on by the deep discharge protection circuit. If the voltage to the post-regulator rises
to +9.7 VDC or greater, the transistor switch remains on. If at any time, the voltage
drops below +9.7 VDC, the transistor turns off and the power switch must be
recycled to restart the instrument. This operation prevents discharge of the battery
below +10 VDC. Such a discharge could cause a reverse charge in a weak cell,
resulting in permanent cell damage.
Primary Circuit
The post-regulator is a boost switching regulator that increases its input voltage to
a constant +16.2 VDC output. This voltage is supplied directly to the processor for
large loads, such as the display heater, electroluminescent backlight, and options
port. The post-regulator also supplies a DC-to-DC converter that generates
"5 VDC and "15 VDC for use in the instrument.
Status signals indicating whether the instrument is running on AC line voltage or
the battery, and if the battery is approaching turn-off level, are supplied to the
instrument by the deep-discharge protection circuits.
The AC line power is received by the connector in the EMI filter (FL1). This filter
prevents high frequency signals generated in the instrument from being conducted
back to the AC power line. The line voltage is fused (F101) and switched (S201)
to the primary step-down transformer (T201). Both the switch and the fuse can be
accessed from the outside of the instrument via covers on the rear of the cabinet.
The primary of T201 is wound in two identical sections. These sections are
connected by S201 (in parallel for 110 VAC operation or in series for 220 VAC
operation). The secondary of T201 is connected by a short two-wire cable to the
Power Supply Board. The MOV (R101), across one of T201’s primaries, protects
the power supply if 220 VAC is applied while S2011 is in the 110 VAC position.
Fuse F101 will open in this event.
Pre-Regulator
1502C MTDR Service Manual
The secondary voltage is full-wave rectified by CR1010 and filtered by capacitor
C1010. The large value of this capacitor allows it to supply energy to the instrument
between half cycles of the line voltage.
5–5
Circuit Descriptions
Integrated circuit U1010 is a pulse-width modulator switching regulator controller.
It oscillates at approximately 70 kHz and provides drive pulses to switching
transistors Q1010 and Q1011. The output pulses from these transistors are filtered
to DC by flyback rectifier CR2010, choke L1010, and capacitors C2010 and C2012.
The resulting +16.6 VDC is fed back to the regulator U1010 by voltage divider
R1016 and R1015. It is then compared to a +2.5 VDC reference voltage from,
U1011. T o increase the output voltage, U1010 increases the pulse width of the drive
to Q1010 and Q1011. T o reduce the output voltage, U1010 decreases the pulse width
to Q1010 and Q1011. This assures that a constant +16.6 VDC is maintained.
Resistor R1010 acts as a current sensing shunt in the pre-regulator return line. In the
event that a circuit fault draws excess current, the voltage developed across R1010
(and filtered by R1011, R1012, and C1011) will cause U1010 to reduce the pulse
width of the pre-regulator. This protects the pre-regulator from damage due to
overload.
Battery Charger
Deep Discharge
Protection
The battery charger consists of a linear regulator integrated circuit, U2010, and
associated components. U2010 is connected as a current source, drawing current
from the +15.8 VDC and supplying it to the battery through T2012. The voltage
drop across T2012 is fed back to U2010 through diode CR2014 to control charging
current at a nominal 150 mA. Diode CR2013 and voltage divider R2010 and R2011
provide a voltage clamp to U2010’s feedback terminal to limit the maximum voltage
that can be applied to the battery through CR2015. As the voltage R2012 and
CR2015 approaches the clamp voltage, battery charging current is gradually
reduced to trickle charge.
Rectifier CR2015 prevents battery discharge through the charger when AC line
voltage is not present. Rectifier CR2012 allows the battery to power the instrument
when AC power is not present.
Pre-regulator or battery voltage is applied to Q2011 and Q2012 when the instrument
power switch is pulled on. The rising voltage causes Q2011 and Q2012 to turn on
due to the momentary low gate voltage while C2011 is charging. During this time,
voltage comparator U1020A compares the switched voltage to a +2.5 VDC
reference from U1022. If the voltage is greater than +9.7 VDC, U1020A turns on,
drawing current through Q2010 and R2015 to keep the gates of Q2011 and Q2012
near ground and the transistors turned on. If the voltage is less than +9.7 VDC (or
drops to that value later), U1020A and Q2010 turn off, allowing C2011 to charge
to the input voltage and turn off Q2011 and Q2012. When turned off, the deep
discharge protection circuit limits current drawn from the battery to only a few
microamperes.
5–6
Post-Regulator
The post-regulator receives from +9.7 to +15.5 VDC and boosts it to +16.2 VDC
by switching Q2022 on and off with a pulse-width modulated signal. When Q2022
is turned on, input voltage is applied across choke L2020, causing the current in
L2020 to increase. When Q2022 is turned off, the stored energy in L2020 will cause
1502C MTDR Service Manual
Circuit Descriptions
the current to continue flowing through CR2021 to filter capacitor C2025. Due to
its stored energy, the voltage developed across L2020 adds to the input voltage,
allowing C2025 to be charged to a voltage greater than the input.
The switching of Q2022 is controlled by pulse-width modulator U1023. The
post-regulator output voltage is fed back to U1023 through R1025 and R1024 and
compared to the +2.5 VDC reference from U1022. Low output voltage causes wider
pulses to be supplied to Q2022, storing more energy in L2020 during each pulse.
This results in a higher output voltage. High output voltage, however, reduces pulse
width and reverses the preceding process.
U1023 oscillates at approximately 80 kHz and supplies a synchronizing signal to
the pre-regulator at that frequency when the instrument is operating on AC power.
This raises the pre-regulator frequency to the same 80 kHz. This synchronization
eliminates beat frequency interference between the two regulators.
The synchronizing signal from U1023 is also supplied to Q2021, where it is
amplified to CMOS levels and buffered by gate U2030A. The signal is then used
to clock flip-flop U1024B to produce a 40 kHz square wave output at Q and Q
square waves are buffered by other U2030 inverters and used to drive DC-to-DC
transistors Q2030 and Q2031.
. These
DC-to-DC Converter
Processor System
Introduction
Transistors Q2030 and Q2031 apply push-pull power to the primary of T1030 at
40 kHz by switching the +16.2 VDC alternately between the primary windings. The
resulting transformer secondary voltages are rectified and filtered by CR1034,
C1032, C1033, and C1034 to produce +15 VDC and –15 VDC. Other secondary
voltages are rectified and filtered by CR1030, CR1031, CR1032, CR1033, C1030,
C1031, and C1037 to produce +5 VDC and –5 VDC.
Diodes CR2031 and CR2030 rectify the primary voltage and clamp it to the voltage
level that is across C2031. This prevents voltage transients caused by the rapid
switching of Q2030 and Q2031 and prevents the leakage inductance of T1030’s
primary from creating excessive voltage stress. R2030 provides a discharge path
from C2031. T1031 and C1036 provide additional filtering of the +16 VDC supply .
The processor system consists of the following:
H Microprocessor
H Address Decoding and Memory
H Interrupt Logic
The processor system provides control and calculation functions for the instrument.
A block diagram of the processor system is shown in Figure 5–4 (next page).
1502C MTDR Service Manual
5–7
Circuit Descriptions
An eight-bit microprocessor, clocked at 5 MHz, provides the processing capability
in a bus-organized system. Instructions are read from the program memory EPROM
and executed by the microprocessor to accomplish essentially all instrument
functions. Random access memory is connected to the microprocessor through its
data and address busses, allowing it to store and retrieve control, video, and display
data, as required.
5 MHz
CLOCK
MICROPROCESSOR
ADDRESS
PROGRAM
MEMORY
EPROM
RANDOM
ACCESS
MEMORY
ADDRESS
DECODING
DATA
SELECT
INTERRUPT
LOGIC
INTERRUPT AND
STATUS INPUTS
DATA SELECT AND
ADDRESS SIGNALS
TO CIRCUITS AND
OPTIONS PORT
Figure 5–4: Processor Block Diagram
The processor communicates with all other instrument circuits via the address, data,
and select signals, and receives requests for service from those circuits via the
interrupt and status signals. Select signals are generated in address decoding circuits
under control of the processor and used to read or write data from a circuit, or to
trigger a circuit function. Interrupts from those circuits are combined in the interrupt
logic to generate an interrupt request to the microprocessor. The processor responds
by reading a data word from this logic to determine the source of the interrupt, or
status data, and then performs the required service routine.
5–8
Microprocessor
The microprocessor, U1023, is a single chip processor using Z80 architecture
constructed in high-speed CMOS logic. Each data word, or byte, is eight bits wide
and the microprocessor has a 16-bit address capability , allowing it to address up to
65,536 memory locations. The processor’s 5 MHz clock is derived from a crystal
oscillator in the timebase circuits.
When +5 VDC power is applied to C1030 and R1032, the rising voltage
momentarily applies a positive signal to the input of gate U1031B. The resulting
1502C MTDR Service Manual
Circuit Descriptions
negative pulse at the gate output is supplied to U1023’s reset input, causing the
microprocessor to start at the beginning of its programmed routine each time power
is applied.
Address Decoding and
Memory
Program Memory
(EPROM)
RAM
The 16-bit address space of Z80 processor U1023 is divided into five primary areas.
They are:
H Program Memory (EPROM) space H RAM space H Non-volatile RAM space H Display RAM space H Enable and Select Signal space
The program memory is stored in 64-kilobyte (kb) EPROM U2020, which is
divided into two 32–kb bank-switched halves. Both halves occupy locations
OOOOH to 7FFFH in the processor’s address space. The most significant address
bit on the EPROM, which determines which bank is addressed, is set by flip-flop
U2030A. This bank-switching flip-flop can be toggled by the processor with two
select lines, decoded in the enable and select signal address space. The select signal
for the EPROM is generated by combined address line A15 with the MREQ signal
in U1045A. Whenever the processor addresses a location where A15 is not set, the
program memory will be selected to place data on the bus.
The first RAM is eight-kilobyte memory U1021, selected by a signal generated by
a 1-of-8 decoder, U1022. This decoder operates on the three most significant address
bits (A
selection of a particular
, A14, A13) in combination with MREQ. Each of its decodes represents a
15
1
/8 th of addressable locations. The first four decode signals
are not used because they are located in the program memory space. The fifth decode
is the select signal for the first RAM, occupying locations 8OOOH to 9FFFH.
Non-Volatile RAM Space
Display RAM Space
Enable and Select Signal
Space
1502C MTDR Service Manual
The second RAM is also an 8-kb memory, U1020, made non-volatile by lithium
battery BT1010 and non-volatile memory controller U1010. The select signal for
this RAM is generated similarly to that for the first RAM with the sixth
1
/8 th decode
of U1022. This decode occupies AOOOH to BFFFH.
The display RAM is also an 8-kb memory, U1040, located in the display module.
It is selected by the seventh decode of U1022. It occupies locations COOOH to
DFFFH.
The remaining addressable space is used to generate enable, select, or trigger
signals, which read, write, and control other circuits of the instrument. The eighth
1
/8 th decode signal of U1022 is used to enable four other 1-of-8 decoders: U2021,
U2022, U2024, and U2026. These four decoders are further selected by the four
5–9
Circuit Descriptions
combinations of A12 and A11 and operate on A10, A9, and A8 to generate the enable,
select, and trigger signals CS00 through CS31. These occupy the remaining address
space, locations EOOOH to FFFFH.
An automatic wait state is inserted for all circuits selected by U2022. The wait state
is used by the processor to compensate for the slow access times of U2041, U2046,
and U4020 on the Main Board; U2023 on the Front Panel Board; and U2040 on the
display module. The wait request is generated by U1041.
The select signals from U2024 are also modified through U1043B by a 200-ns pulse.
This pulse is created from gates U1042B, U1031C, U2040C, and J-K flip-flop
U2033A. This circuit creates a write pulse that ends prior to the completion of the
processor bus cycle, thus meeting data hold time requirements for some selected
ICs.
Additional Decoding
Interrupt Logic
Option Port Interface
The most significant address bit on the EPROM is set or reset by bank-switching
flip-flop U2023A. Another control signal, heat disable, is generated by a similar
flip-flop, U2023B. This is also toggled by two select lines.
The interrupt logic consists of an eight-bit tri-state buffer, U1032, and gates U1030
and U1031D. Six interrupt requests signals are logically OR’d by U1030, then
inverted by U1031D and applied to the microprocessor interrupt request input. Five
of the interrupts are received from the video ADC, the digital timebase, a real-time
counter, the front panel control ADC, and from the Option Port connector . The sixth
interrupt input is unused.
The six interrupt requests and two power status signals are connected to pull-up
resistors R1033 and the inputs of buffer U1032. When the microprocessor responds
to an interrupt request, it selects U1032, allowing the eight inputs to that device to
be placed on the data bus for reading.
The processor system outputs six control signals to the Driver/Sampler module.
These signals are loaded from the data bus into latch U3010 by a select signal from
the address decoder. These signals are used by the 1502C Driver/Sampler and the
Option 06 adapter (if equipped).
5–10
Introduction
The option port interface consists of the following:
H Supply Controller
H Buffers
H Output Latch
The option port interface provides the connection between the processor system and
external options. This port has a unique protocol that must be followed for proper
1502C MTDR Service Manual
Circuit Descriptions
and safe operation. Further information can be obtained by contacting your
Tektronix customer service representative. A block diagram of the option port
interface is shown in Figure 5–5.
The processor system provides all the data and control for the interface. Data,
Address, and Control lines are all buffered for increased drive. The power to the
option port is switchable to reduce power consumption, if necessary. The other
outputs are available for control and protocol purposes.
Supply Control
SWITCHED
POWER
POWER
DATA
ADDRESS
CONTROL
SUPPLY
CONTROLLER
BUFFERS
OUTPUT
LATCH
Figure 5–5: Option Port Interface Block Diagram
The +16 VDC and +5 VDC power outputs to the option port are switched supplies
controlled by the microprocessor system. CS14
and CS15 are used to set and clear
flip-flop U1011B. This feeds comparators U1012A and U1012B. The positive (+)
input to the comparators is set at 2.5 volts, so the CMOS flip-flop will drive the
negative (–) terminals above and below that voltage level. The comparators are
powered with a +16 VDC and a –12 VDC source to give a good output swing in
controlling the FET switches.
1502C MTDR Service Manual
The output of U1012A controls the +16 VDC switch and is pulled up via a 20 kW
resistor, R201 1. The output is also passed through two 100 kW resistors, R2012 and
R2013, to prevent the FET s from being over-driven. Two parallel FET s, Q201 1 and
Q2012, control the supply.
T o reduce the instantaneous draw from the instrument supply when first turning the
switch on, capacitive feedback is used (C2016). This feedback slows the turn-on
time, allowing a capacitive load to be charged without affecting the instrument
supply. A stabilizing 100 W resistor, R2010, is also located in the feedback loop.
5–11
Circuit Descriptions
NOTE. There are specified limits to this type of circuitry. Load specifications must
be followed.
The arrangement of the +5 VDC switch is similar except that a 10 kW to 100 kW
resistive divider is used to ensure the switch has a definite turn-on. A single FET,
Q1010, controls the +5 VDC output.
Buffers
Output Latch
Option Port Wiring
Configuration
Data lines to the option port pass through the bus transceiver, U201 1. Address lines
RD’
and WR’ are driven by U2012. CS22, from the processor system, enables these
drivers with RD
controlling the transceiver direction. U2012 outputs are pulled up
by the switched +5 VDC supply, via R2015. The data lines are pulled down via
R2014.
WR’ is a modified write pulse 200 ns long, created to give a rising edge prior to the
disabling of the drivers. This pulse is created by flip-flop U2033A.
The output latch U1011A is controlled by A
and A1, with select signal CS10. The
0
output of this latch is optionally used in the interface protocol.
Two more lines are used in the option port interface. IR4
is active low when creating processor interrupts. R-T TRIG
is an interrupt signal that
is also available at the
interface. This is the trigger pulse generated in the analog timebase.
D
0
D
1
D
2
D
3
D
4
D
5
D
6
D
7
A0’
A1’
A2’
A3’
RD’
WR’
CS22
Label
J2010
(on Main Board)
3 2
1 1
24 25
22 24
20 23
18 22
16 21
14 20
12 19
10 18
8 17
6 16
7 4
5 3
9 5
Option Port
(D-Connector)
5–12
1502C MTDR Service Manual
Circuit Descriptions
Video Processor
Introduction
J2010
Label
IA
IR4
R-T TRIG
SW+16
(on Main Board)
11 6
13 7
2 14
25
23
+16
RTN
21
19
SW+5
+5
RTN
17 9
4
15
The video processor system consists of the following:
H Vertical Position DAC
H Summing Amplifier
H Video Amplifier
H Video DAC
Option Port
(D-Connector)
13
12
11
10
15
8
The video processor receives sampled video from the driver/sampler and outputs a
digitized video signal to the processor system data bus. A block diagram of the video
processor is shown in Figure 5–6.
INTERRUPT
REQUEST
VIDEO
ADC
CONTROL
SUMMER
AMPLIFIER
COMBINED
VIDEO
DATA
CONTROL
VIDEO
AMPLIFIER
Sampled Video
from
Driver/Sampler
DATA
CONTROL
VERTICAL
POSITION
DAC
DATA
BUS
Figure 5–6: Video Processor Block Diagram
Vertical position information is loaded by the processor system into a DAC to
generate a DC signal. Sampled video is combined with this vertical position DC
voltage in a summing amplifier in order to allow vertical positioning of the
displayed waveform.
1502C MTDR Service Manual
5–13
Circuit Descriptions
The combined video and position signal is amplified by the user-selected gain in the
video amplifier. Gain of the amplifier is set by the processor system via the data bus
and video amplifier select signal.
The amplified video is digitized by the video ADC upon receipt of a control signal
from the processor system. The processor is notified by the ADC interrupt request
when the conversion has been completed. The processor then reads the value via the
data bus.
Vertical Position DAC
Summing Amplifier
Video Amplifier
The vertical position DC voltage is generated by a digital-to-analog converter
consisting if U2046 and U3041. DAC integrated circuit U2046 receives a +2.5 VDC
reference voltage from U3040 and multiplies it by a 14-bit digital value loaded from
the data bus under control of the processor. The resulting current output of U2046
is amplified by operational amplifier U3041 to a proportional voltage of zero to
–2.5 VDC.
The summing amplifier consists of operational amplifier U8041; input resistors
R8044, R8046, and R8047; and a feedback resistor, R8045. Summation of the DAC
output through R8047 with the +2.5 VDC reference through R8046 causes the
vertical position signal range to be enlarged and shifted to achieve an effective
output of –2.5 VDC to +2.5 VDC.
Sampled video, through R8044, is summed with the vertical position signal at the
input node of U8041. Resistor T8045 determines the gain of U8041 and is paralleled
with C8040 to reduce high frequency gain for noise reduction. The sampled video
input may be observed at TP9041.
Combined video from the summing amplifier is further amplified by a three-stage
programmable video amplifier.
The first stage of this amplifier consists of amplifier U7040, voltage divider T8040
through R8043, and analog multiplexer U8040. Voltage gains of 0, 16, 32, or 48 dB
are achieved by switching U8040 to connect one of the four points from the resistive
voltage divider to the inverting input of U7040. This causes the amplifier gain to
be equal to the attenuation factor of the voltage divider point selected.
5–14
The second stage consists of amplifier U5040, voltage divider R6040 through
R6047, and analog multiplexer U6040. This stage operates similar to the first stage
except eight voltage gains are provided from 0 to 14 dB in 2-dB steps.
The third stage consists of amplifier U3042, voltage divider T4040 through R4047,
and analog multiplexer U4040. This stage operates similar to the first and second
stages except eight voltage gains are provided from 0 to 1.75 dB in 0.25-dB steps.
Gain of each of the three amplifier stages is controlled by the processor system by
loading latch U2044 with the appropriate 8-bit word from the data bus. Digital word
1502C MTDR Service Manual
Circuit Descriptions
00 (all 0s) selects 0 dB gain and word FF (all 1s) selects 63.75 dB gain. All
intervening values of 0.25 dB multiples are similarly chosen.
The output of the video amplifier is filtered by R2040 and C2043 for noise
reduction, then sent to the analog-to-digital converter. The output may be observed
at TP4040 (see Figure 5–7).
20nS
Video Analog-to-Digital
Converter
Timebase
Introduction
500mV
Figure 5–7: Video Processor Output
The output of the video amplifier is converted to its digital equivalent value by ADC
device U2041. The conversion is done using successive approximation technique
to compare the video voltage to the +2.5 VDC reference from U3040. The device
is clocked by a 1.25 MHz clock derived from the timebase oscillator, and completes
its 12-bit plus sign conversion in approximately 100 ms.
Gate U2040 provides an OR function for the ADC start conversion trigger and read
pulses from the processor system. Either pulse selects the ADC for control and
concurrent pulses select the trigger (WR
Upon completing a conversion, the processor system is notified by an interrupt
request (IR0
The timebase circuits receive video sample time delay values in digital form from
the processor system and generate precisely timed strobes to the driver/sampler
circuits. Digital counters determine the delay in 50 ns multiples, and analog circuits
further define the delay to fractions of that period. A block diagram of the timebase
circuits is shown in Figure 5–8 (next page).
) from U2041.
input) or read (RD input) functions.
1502C MTDR Service Manual
5–15
Circuit Descriptions
The digital portion of the timebase contains a clock generator that develops all
frequencies used in the instrument electronics.
DATA
CONTROL
DATA
CONTROL
Clock
Generator
2.5 MHz
PRT
Counter
2.5 MHz
Course
Delay
Counter
SYSTEM
CLOCKS
DIGITAL
TIMEBASE
20 MHz
5 MHz
2.5 MHz
1.25 MHz
625 KHz
20 MHz
Pulse
Former
20 MHz
Fine
Delay
Counter
TIMEBASE
INTERRUPT
DRIVER
TRIGGER
RAMP
TRIGGER
PROCESSOR
CONTROL
Time
Delay
Circuit
Correction
Delay
Cal
Ramp
Cal
50 ns analog
delay cal
DATA
CONTROL
Timebase
Vref
Stobe
Driver
Ramp
Generator
Voltage
Comparator
Analog
Timebase
DAC
PULSE
GENERATOR
Strobe
Driver
ANALOG
TIMEBASE
SAMPLER
5–16
Figure 5–8: Timebase Block Diagram
A programmable digital counter, clocked at 2.5 MHz, is used to determine the PRT
(pulse repetition time) of the driver/sampler test pulse. The 1502C is programmed
with a PRT of 350 ms. The output of the PRT counter is used to trigger a delay
counter, also clocked at 2.5 MHz, to provide coarse (400-ns resolution) digital time
delay. The end of this time delay triggers a fine delay counter, which is clocked at
20 MHz, providing 50-ns resolution to the sampler time delay . Both the coarse time
delay and the fine delay counters are programmed by the processor via the data bus.
The end of the coarse delay is used to generate a timebase interrupt request to the
processor to inform it that a sample is being taken and a timebase update is required
for the next sample.
The output of the fine delay counter is provided to the analog timebase circuits for
further delay control to become the sampler trigger. The beginning of the coarse
delay counter period is detected by a pulse former, which generates a driver trigger
for the analog timebase.
1502C MTDR Service Manual
Circuit Descriptions
The analog timebase circuits receive the driver and sampler triggers and provide
strobes to the driver/sampler. The driver trigger is delayed by an analog time delay
and amplified by a driver circuit to provide the driver strobe.
The ramp trigger is used to start a linear voltage ramp generator. A voltage
comparator detects the time when this ramp reaches the programmed voltage of the
timebase DAC (digital-to-analog converter) and signals a driver to produce a strobe
for the video sampler. The timebase DAC is programmed by the processor to
provide a voltage proportional to the portion of the 50-ns time delay period desired.
Timebase control by the processor system is shown in Figure 5–9. Each period of
the pulse rate, the processor calculates a new 33-bit digital time delay value for the
next sample to be taken. The sixteen most significant bits of this value are loaded
into the coarse delay counter, causing it to count that number of 2.5 MHz clock
periods before starting the fine delay counter.
33-BIT
DIGITAL TIME
DELAY VALUE
MSB LSB
3 BITS16 BITS 14 BITS
PRT
PULSE
COURSE
DELAY
COUNTER
2.5 MHz
CLOCK
FINE
DELAY
COUNTER
20 MHZ
CLOCK
ANALOG
DELAY
STROBE TO
SAMPLER
Figure 5–9: Timebase Control
The next three bits from the processor time delay value are loaded into the fine delay
counter. This counter starts at the end of the coarse delay, and counts the selected
number of 20 MHz clock periods (o through 7) before triggering the analog delay.
The analog delay circuit receives the 14 least significant bits of the time delay word.
A digital-to-analog conversion provides a proportional voltage, which is compared
to a linear voltage ramp to produce the programmed time delay (o to 50 ns).
The timing diagram in Figure 5–10 (next page) shows the combined effects of the
three time delays. The output of the PR T counter, waveform (a), begins the coarse
delay (b). The falling edge of this signal triggers the driver strobe (c), which causes
a pulse to be applied to the cable test output.
1502C MTDR Service Manual
5–17
Circuit Descriptions
PRT
COUNTER
COURSE
DELAY
COUNTER
(a)
(b)
16 BIT
PROGRAMMED DELAY
DRIVER
STOBE
FINE
DELAY
COUNTER
RAMP
TRIGGER
[EXPANDED]
RAMP
GENERATOR
[EXPANDED]
SAMPLER
STROBE
(c)
3 bit
prgm
delay
400 ns
(d)
(e)
14 BITDAC
OUTPUT
(f)
(g)
Figure 5–10: Combined Effects of Time Delay
At the end of the coarse delay, the rising edge of this signal enables the fine delay
(d), which produces a single ramp trigger pulse after the programmed delay. This
pulse is shown expanded in waveform (e). The ramp generator waveform (f), also
shown expanded, has a linear voltage ramp beginning on the falling edge of the
trigger. This voltage is compared to the voltage from the timebase DAC, such that
when the ramp exceeds the DAC voltage, the sampler strobe (g) falls. This falling
edge is used as the sampler strobe for video sampling.
5–18
At the beginning of each sweep, the zero distance reference is calibrated to the
front-panel connector and the length of the analog ramp to 50 ns.
Zero distance reference is calibrated by setting the digital and analog timebase for
zero delay. Then the processor adjusts the driver delay so as to sample at the 10%
point of the pulse. The ramp is calibrated by removing 50 ns of delay (one 50-ns
clock cycle) from the sample trigger and then reinserting it with the analog delay.
The processor adjusts the reference for the timebase DAC so as to sample at the
previous level. This matches the analog delay to the 50-ns period of the clock.
1502C MTDR Service Manual
Circuit Descriptions
4V = 50ns DELAY
∼
∼
0V COMPARATOR LEVEL = 0 DELAY
50 ns DELAY
COMPARATOR LEVEL
SET TO SAMPLE
PULSE AT 10% POINT
ON OUTPUT PULSE
50 ns
COMPARATOR LEVEL SET
SO SAMPLE T AKEN AT 10%
START PULSE
VAR. DELAY RAMP
TO SET DELAY ZERO
POINT ON OUTPUT PULSE
PULSE OUT
10% LEVEL
COMPARATOR
OUTPUT
DELAY ZERO SET
DELAYS
FIXED CIRCUIT
50 ns RAMP SET
50 ns RAMP START
0V = 0 DELAY
20 MHz CLK
TP2031
PULSE TRIG
DIGITAL DELAY
Figure 5–11: Calibration of Delay Zero and 50-ns Analog Delay
1502C MTDR Service Manual
TP9011
TRIG TO
PULSE GEN.
TP7010
TRIG TO
SAMPLER
TP2030
SAMPLE TRIG
5–19
Circuit Descriptions
Digital Timebase
All digital clocks from the instrument are derived from a 20 MHz crystal oscillator,
U2031. Flip-flops U2042A and U2042B divide the clock frequency to 10 MHz and
5 MHz respectively. The 5 MHz output is provided to the microprocessor and to
TP2041.
Gate U2034B decodes one of the four states if U2042 and provides a 5 MHz pulse
to U2033B. Flip-flop U2033B is clocked by the 20 MHz clock and divides the 5
MHz signals to 2.5 MHz synchronously with the 20 MHz. The 2.5 MHz clock is
further divided to 1.25 MHz by U2025A and 625 kHz by U2025B.
The PRT, coarse delay, and real-time counters are contained in a triple, 16-bit,
programmable counter device, U2030. The PRT and coarse delay counters are
clocked at the 2.5 MHz rate. The output of the PRT counter, pin 10 of U2030, is
applied to the trigger input of the coarse delay counter as a start-count signal. The
negative-going pulse from the coarse delay counter, pin 13 of U2030, is input to a
two-stage shift register, U2032C and U2032D. This shift register is also clocked at
2.5 MHz and serves to delay the signal and reduce its skew relative to the 20 MHz
clock. The Q
to a three-stage shift register, U2036B, U2036D, and U2036A, which is clocked at
20 MHz from inverter U2034A. The leading edge of the pulse is decoded by NAND
gate U2045B, which also ANDs the signal with the 20 MHz clock from inverter
U2045A. The resulting driver trigger pulse is a negative-going pulse of nominally
25 ns width. The falling edge of this pulse is determined by the edge of the 20 MHz
input to gate U2045B and is used as the driver trigger.
(inverted output) of U2032C is a positive-going pulse that is supplied
Analog Timebase
The coarse delay pulse from shift register U2032D and U2032C us decoded by NOR
gate U2034C to detect the pulse rising edge (end of the negative pulse). The
resulting positive pulse is 400 ns wide (one cycle of the 2.5 MHz clock). This pulse
is shifted through flip-flop U2036C to synchronize it with the 20 MHz clock and
applied to the count enable input of U2037, a four-bit programmable counter.
Counter U2037 will have been preset to a count of 8 through 15 by the processor
through latch U2043 with CS11
count exactly eight times at the 20 MHz rate, thus passing through count 15 after
0 through 7 clock pulses. The terminal count (TC) output of U2037 is a decode of
count 15. Thus this signal creates the fine delay pulse after the programmed delay .
This positive-going pulse is gated with the 20 MHz clock by NAND gate U2045C
to provide a 25 ns negative-going pulse for the ramp trigger . Ramp timing is derived
from the trigger falling edge.
The end of the coarse delay, detected by gate U2034C, is used to clock U2027A,
which generates an interrupt request to inform the processor that a sample is being
taken. An acknowledge pulse, CS16
The logic level driver trigger from the digital timebase is first amplified by transistor
stage Q9021. The trigger is capacitively coupled through C8022 and R9027 to shift
it to analog levels. The collector of Q9021 is clamped to –0.5 VDC between pulses
by CR8020 and rises to +6 VDC peak during the 25 ns pulse. This signal is applied
. While the count enable pulse is present, it will
, from the address decoder resets this flip-flop.
5–20
1502C MTDR Service Manual
Circuit Descriptions
to C8021 through R8025 to generate an exponentially rising pulse of about 4 VDC
peak during the pulse width.
Dual transistor Q8020 is a differential amplifier that is used as a voltage comparator
to detect when the pulse on C8021 has reached the DC voltage level set through
U4021B and R8023 by the zero-distance calibration circuit. This DC voltage level,
from zero to 4 VDC, allows setting the time when the voltage comparator switches
(a range of about 20 ns). Dual transistor Q9020 is connected as a current source,
providing a constant 2-mA bias to the emitters of Q8020. Between pulses, this
current flows through Q8020B. When the exponential pulse reaches the adjustable
voltage level, the current is rapidly transferred to Q8020A, causing a negative-going
pulse at R8020. This pulse is coupled to the output stage, Q9010, through C9020
and R9020. Transistor Q9010 is biased to 0.5 mA between pulses to obtain fast
turn-on, and provides a positive-going 5 VDC pulse to U8010B and U8010C.
Flip-flop U7010A is set or reset by the processor to steer the pulse either to the
option port or the driver. The negative-going pulse from gate U8010B or U8010C
is logically OR’d by U8010A, then applied to C9010 and R9010. This pulse is fed
back to the input of the gates U8010B and U8010C through CR9010 to obtain a
one-shot action, which stretches the driver strobe pulse width to 5 ms. The driver
strobe is made available at TP9011.
The ramp trigger pulse from the digital timebase is AC-coupled by C3040 and
R3041 to Q4040. Diode CR3031 allows the negative-going pulse to pass directly,
while R3040 limits the input current sue to the re-charging of C3040 between
pulses. The output of Q4040 is held at ground by L5030 between pulses and rises
to 6 VDC during the pulse. Choke L5030 is center tapped to provide an equal
negative-going pulse at its undriven end. This pulse is fed through C5033 and
R4032 to the emitter of Q4031 to obtain positive feedback to Q4040. This forms a
one-shot circuit with the pulse width determined by C5033 and R4032. The 25 ns
ramp trigger pulse is thus stretched to about 80 ns at L5030.
Dual transistor Q5032 operates as a current source, providing a constant 5-mA
current, which is used to charge C5032 to create a linear voltage ramp. Between
ramp trigger pulses, this current is conducted through CR4032 and L5030 to ground,
creating a voltage of 0.5 VDC on C5032. The positive one-shot pulse from Q4040
turns off CR4032 and directs the charging current to C5032. The negative-going
pulse from L5030 is connected to C5032 through CR5030 to provide a cancelling
effect for the positive pulse being coupled through the capacitance of CR4032.
The linear rising voltage pulse from C5032 is buffered by source-follower Q5031
and emitter-follower Q5030 to provide a low output impedance and prevent loading
the ramp. Transistor Q7030 provides a constant 2-mA bias current to junction FET
Q5031.
The ramp voltage is AC-coupled to voltage comparator Q7021 by C7030 to remove
the DC offset voltage developed in the preceding circuits. A small negative DC
voltage of approximately –200 mV is added by voltage divider R7032 and R7025
to hold the voltage comparator off between pulses.
1502C MTDR Service Manual
5–21
Circuit Descriptions
Voltage comparator Q7021 is biased at 2 mA by dual transistor Q5020. During the
linearly rising ramp voltage, it compares the ramp to a programmed DC sample
reference voltage produced by the timebase DAC circuit. When the ramp reaches
the sample reference value, Q7021A rapidly turns on to produce a negative-going
signal across R7024. This pulse is coupled through C7022 and R7021 to turn on
Q6020, providing a positive pulse to the base of Q7020. The negative-going sampler
strobe coming from Q7020 is supplied to the sampler and to TP7010.
Timebase DAC U4020 and amplifier U5010 inverts and multiplies V
REF
by the
14-bit digital word loaded by the processor. It is filtered for noise by R7026 and
C5023 and connected to comparator Q7021 through R7027 to set the analog delay
(0 to 50 ns).
To calibrate the analog delay to 50 ns, the processor sets IR2
(IR2 high) and loads
a new 12-bit word in latches U3021 and U3022 (max 1-bit change per sweep) with
chip selects CS11
and CS12. DAC U3023 multiplies the reference current (1 mA
set by R3020) by the digital word from the latches. The DAC output current and
the current from the last two LSBs (which comes from the latches through R3031,
R3033, R3039, and R4020) are summed by U4021A and forced through R4021.
This develops a correction voltage at TP4020 of "5 VDC and a sensitivity of
2.5 mV per bit (the currents from the LSBs have been complimented by the
processor to correct their phase). The DAC circuit is designed to nominally run at
half of full dynamic range (2048/4096) of 2 mA, that generate 1 mA of current at
the summing node. That current is balanced out by 1 mA of current from R4020,
giving a nominal output of zero volts at TP4020 and TP4021.
U5020, R5020, R5021, and C5021 scale the correction signal (up to "5 VDC) at
TP4020 to "0.4 VDC at V
current to offset V
to a –4 VDC "0.4 VDC (equivalent to "5 ns) correction
REF
of U4020. Resistors R5023 and R5022 furnish a
REF
signal to the 50 ns analog delay.
To calibrate, the zero-distance delay (IR2
) is set low, and through R3037 and
CR3030, turns on Q3030, whose collector (through R3036 and R3035) raises the
cathode of CR4030 to +6 VDC. This allows R4023 to turn on Q4030. Capacitor
C4022, through R4030 and Q4030, is charged to the new corrected level at TP4020
that was asked for by the processor. The correction voltage on C4022 from buffer
amplifier U4021B is scaled by voltage divider R8023, R8022, and R8021 from a
range of "5 VDC to a range of zero to 3.5 VDC. This voltage is applied to the base
of comparator Q8020B, which provides "10 ns of zero-distance delay adjustment.
Components C3048, R3042, R2032, C3047, R2034, and C8024 are used to reduce
jitter and cross-coupling between circuits.
5–22
1502C MTDR Service Manual
Driver/Sampler
Circuit Descriptions
Introduction
The front-end consists of:
H Hybrid Sampler/Step Generator
H Second Sampler
H First Sampler Bridge Bias Generator
H Trigger Pulse Shapers
H Power Supply Conditioning
The function of this board is to generate the step test signal and to sample and hold
the reflections from the cable under test. A block diagram of these circuits is shown
in Figure 5–12 (next page).
Most of the primary active circuitry is located within the hybrid. The balance of the
Driver/Sampler Board is dedicated to interfacing with the rest of the instrument.
The step generator is triggered by a negative pulse from the Main Board. One of the
trigger pulse shapers stretches this to 25 ms to set the length of the output step. The
0.6 V adjustable power source sets the “on” voltage for the output step.
The sampler is also triggered by a negative pulse from the Main Board. Inside the
hybrid, this trigger causes the strobe generator to apply 50-ps pulses to turn on the
bridge, capturing a portion of the input waveform. This sample is stored outside the
hybrid in the second sampler to reduce droop rate. The stored signal goes two places:
back to the Main Board as the video output, and to the bridge bias circuit, which
holds the sampling bridge off between samples.
Second Sampler
1502C MTDR Service Manual
The video signal from the hybrid is sent to the second sampler. The second sampler
reduces the droop rate to about 1 LSB/ms. This is accomplished by buffering the
signal through U2050B and storing it in C2053 via the FET switch, Q1060. The FET
is strobed by the one-shot U3030B for 5 ms after the sample is taken. The voltage
stored on C2053 is buffered by op-amp U2050A, then inverted and amplified by
U1050A. The strobe signal for the FET can be observed at TP2060, and the inverted
video output at TP1060. The signal from the second sampler buffer, U2050A, is also
fed to the bridge bias amp, U1070, via R1060.
5–23
Circuit Descriptions
Step trigger
Sample trigger
Inverted
Video Out
Figure 5–12: Driver/Sampler Block Diagram
± 12V
Regulator
25 µs
One Shot
5 µs
One Shot
–1.6
± 12V± 15V
On board
supply
0.6 V
Adjustable
source
Step
Generator
Sampler
strobe
generator
2nd
Sampler
Hybrid
Sampling
bridge
Front
panel
cable
connector
Bridge
bias
+B
–B
Bridge Bias
Trigger Pulse Shapers
Power Supply Conditioner
The bridge bias for the first sampler is set by U1070. With a zero voltage input
signal, the circuit holds "2.0 V on the bridge inputs. As the input signal moves, the
4 V window also moves to stay centered around it. This centering is accomplished
by feeding part of the output of U2050A into the bridge bias circuit. The outputs of
the bridge bias circuit are available on TP1020 and TP1021.
There a\re two incoming triggers: the sample and the step. Both require modification
before they are usable by the hybrid. The sample trigger is a 30-to-50-ns negative
TTL signal. This pulse is buffered by Q2030, then coupled to the hybrid through
T1020. This provides a differential drive that can have common-mode voltage on
it. The sampler pulse is also stretched to 5 ms by U3030B to strobe the second
sampler. The step trigger , GEN TRIG
, is a 3-to-5-ms negative TTL signal, stretched
to the proper 25 ms pulse length by U3030A. CR3020 and CR3021 provide a logic
OR of the incoming signal and the output of the one-shot. This prevents the
introduction of jitter on the trigger signal. The OR output can be observed at
TP3020.
There are seven power supplies for the hybrid: "5 V
, "5 VP, "12 V, and +0.6 V.
S
The "5 V supplies come on board as 5 V, so they require no regulation, but are
merely filtered before being used by the hybrid and the board. The "12 V supplies
enter the board as "15 V, so the necessary filtering and regulation is accomplished
by U3070 and associated circuitry. The +0.6 V supply is used by the hybrid to set
5–24
1502C MTDR Service Manual
Front Panel
Circuit Descriptions
the output step height. It is referenced to the +5 V supply and controlled by U1050B
and Q1030.
The +0.6 V supply is adjustable via R1042 to allow the offset of the step generator
to be zeroed out. CR1040 temperature compensates the +0.6 V supply against
variations in the hybrid. The test points for these supplies are as follows:
+5 V TP1083
–5 V TP1084
+12 V TP1080
–12 V TP1081
+0.6 V TP1030
Ground TP1082
Introduction
Push Button Switches and
Latches
The Front Panel Board consists of the following circuits for these controls:
H Push Button Switches and Latches H Rotary Binary Switches H Resistive Shaft Encoders H Analog-to-Digital Converter for Shaft Encoders
The Front Panel Board consists of the following circuits for the display module:
H Electroluminescent Backlight Switch and Power Supply
H Display Heater Circuitry
H Display Drive Voltage (Contrast) Temperature Compensation
The Front Panel Board contains most of the instrument control as well as some
circuitry for the display module. A block diagram of the Front Panel Board is shown
in Figure 5–13 (next page).
The push button switches are normally open momentary switches When depressed,
these switches tie the inputs of NOR gate latches U3021, U3022, and U3023 to +5
VDC, setting the latches. The latches are reset by control signal ADCRD. The
processor updates the instrument configuration by periodically reading the state of
the latches through multiplexers U2024, U3025, and U3031.
1502C MTDR Service Manual
These switches control:
H MENU
H VIEW INPUT
H VIEW STORE
H VIEW DIFF
H STORE
5–25
Circuit Descriptions
Push Button Switches
MENU
VIEW INPUT
VIEW STORE
VIEW DIFF
STORE
IMPEDANCE
NOISE FILTER
FEET/DIV
PULSEWIDTH
Vp
L
A
T
C
H
E
S
M
U
L
T
I
P
L
E
X
E
R
S
ANALOG-DIGITAL-CONVERTER
50 - Pin
Connector
Data Bus
Address/
Control Bus
Rotary Binary Switches
HORIZONTAL
POSITION
VERTICAL
POSITION
VERTICAL
SCALE
Resistive Shaft Encoder
Figure 5–13: Front Panel Block Diagram
EL
Switching
Circuitry
LCD Heater
Drive Circuitry
LCD Drive
Voltage
Circuitry
EL
Power
Supply
From Temp Sensors
To LCD Heater
To LCD Drivers
To EL Backlight
50 - Pin
Connector
5–26
1502C MTDR Service Manual
Circuit Descriptions
Rotary Binary Switches
Switch Multiplexers
Resistive Shaft Encoders
The rotary binary switches provide a 4-bit binary value, indicating their position.
The outputs are tied to the inputs of the multiplexers. The position of the rotary
switches control the following functions:
H FILTERING, SET REF, SET DELTA
H HORIZONTAL GAIN (DIST/DIV)
H V
H V
COARSE
P
FINE
P
The switch multiplexers are U2024, U2025, U3025, and U3031. These dual
four-channel multiplexers multiplex the switch settings of the push button and
rotary switches onto the data bus. The control signal MUXCS
A
, selects the multiplexers while A0 and A1 determine which switch bank is placed
2
, in conjunction with
on the data bus.
The resistive shaft encoders R1022, R2024, and R3020 are dual-concentric, 360°
rotation potentiometers, with the wipers set 180° out of phase with respect to each
other. The wipers are tied to the analog-to-digital converter inputs of ADC U2023.
The three resistive shaft encoders control the following functions:
H VERTICAL GAIN
H VERTICAL POSITION
H HORIZONTAL POSITION (Cursor)
Analog-to-Digital
Converter
Electroluminescent
Backlight Switch and
Power Supply
The ADC, U2023, is an eight-channel analog-to-digital converter. It converts the
voltages on the wipers of the resistive shaft encoders to a digital value, depending
on the position of the encoders. It also converts the voltage on the display thermistor
(T
) and the chart recorder thermistor divider circuits into digital values
SENSE
representing the corresponding temperatures. The temperature data is used by the
processor to compensate the LCD drive voltage and chart recorder print parameters
for variations in temperature.
The control signal TRIG ADC is used to start a conversion; ADC RD reads the
value; and A
signal EOC
, A1, and A2 select one of the eight channels for conversion. Control
0
notifies the processor of a conversion completion, via the IR3 line.
The EL (electroluminescent) backlight is switched by software. Control signal
LIGHTCS
, with RD or WR, sets or resets (respectively) NOR latch U3020. The
output of the latch is applied to the + side of comparator U2020B; the – side is held
at 2.5 VDC. When the output of the latch is high, the comparator output is +16 VDC,
which turns off the gate of P-channel FET Q1030, turning off power to the EL power
supply, PS2030. When the output is low, the comparator output is 0V, which turns
on the FET , turning on the power to the EL power supply. R1031, C3030, and C3031
serve to filter noise introduced to the +16 VDC supply by the EL power supply.
1502C MTDR Service Manual
5–27
Circuit Descriptions
Display Heater Circuitry
Display Temperature
Compensation
The display heater circuitry regulates the application of power to the display heater
(see Indium T in Oxide Heater later in this chapter for more information). When the
display thermistor divider senses the display temperature has dropped below
+10° C, the heater can be turned on if the control signal HEAT ENABLE
asserted. For reasons of power economy, the chart recorder and display heater are
not allowed to operate concurrently. The processor does this by asserting HEAT
ENABLE while making a chart recording. When HEAT ENABLE is low,
N–channel FET Q2020 is off, making the voltage on the + side of the comparator,
U2020A, approximately +5 VDC. This will allow the + side (chart recorder) to
always be greater than the – side (display thermistor divider voltage). The output
of the comparator will be +16 VDC, which turns off P-channel FET Q1020. This
turns off the power to the display heater.
When HEAT DISABLE
of the comparator will be approximately 2.5 volts. When the display thermistor
divider voltage (– side) is above 2.5 volts (about +10° C), the comparator output will
be 0 V, which will turn on Q1020. This will turn on the heater. As the temperature
rises above +10° C, the thermistor divider voltage will be less than 2.5 V and Q1020
will turn off, shutting off power to the heater.
The LCD drive voltage compensation circuitry adjusts the drive voltage (contrast)
to assure a constant display contrast within the operating temperature range of the
instrument. The display thermistor is attached to the LCD and forms the sensor in
the display thermistor divider circuit. Its output is a voltage related to the display
temperature. This voltage is read by the processor through the analog-to-digital
converter, U2023. The processor uses this voltage value to determine a drive
voltage. This is sent to digital-to-analog converter U2021 via the data bus. The
output of the DAC is amplified to op-amp U2010A and applied as the LCD drive
voltage. As the temperature of the display (thermistor divider voltage) changes, the
processor modifies the drive voltage via the DAC. In this manner, the drive voltage
is compensated due to variations in display temperature. Trimmer potentiometer
R1011 is used to offset the drive voltage produced by U2010A to compensate for
variations in display cells and thermistors.
is high, Q2020 will turn on and the voltage on the + side
is not
Display Module
Introduction
5–28
The display module consists of the following:
H LCD Cell
H Row Driver/Controller Board and Column Driver Board
H Electroluminescent Backlight
H Indium Tin Oxide (ITO) Heater
H Mechanical frame, which supports the above subassemblies
1502C MTDR Service Manual
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