Fix Your Function Generator with Keysight 33250A!

Table of Contents

1. Introduction
2. Overview of the Keysight 33 250A Function and Arbitrary Waveform Generator
3. Issue with the Generator's Output
4. Error Codes and Troubleshooting
5. Block Diagram Analysis
6. Examination of Relays and Amplifier Path
7. Checking Power Rails and Waveform DAC
8. Clock Signal Investigation
9. Resistor Inspection and Replacement
10. Testing the Fixed Generator
11. Conclusion

Article

Introduction

In this article, we will be discussing the troubleshooting and repair of the Keysight 33 250A Function and Arbitrary Waveform Generator. We will delve into the issues faced with the generator's output and the error codes encountered during the self-test. Through a systematic approach, we will analyze the block diagram, examine the relays and amplifier path, check the power rails and waveform DAC, and investigate the clock signal. Additionally, we will inspect and replace faulty resistors and perform tests to ensure the generator is fixed.

Overview of the Keysight 33 250A Function and Arbitrary Waveform Generator

The Keysight 33 250A Function and Arbitrary Waveform Generator is a versatile piece of test equipment that allows users to generate a wide range of waveforms, including sine waves, square waves, and arbitrary waveforms. It offers various output options and parameters to customize the generated signal according to specific requirements. However, in this particular case, the generator is experiencing issues with its output.

Issue with the Generator's Output

Upon powering up the generator, it was noticed that there was no output signal. Despite enabling the output, there was only a slight increase in noise, but no actual waveform was being generated. To diagnose the problem, the self-test feature was utilized, which produced error codes 628 and 629. These error codes indicated issues with the relays in the attenuator path and the amplifier path, respectively.

Error Codes and Troubleshooting

To understand the problems related to the error codes, a thorough examination of the service guide was conducted. The relays located around the 20 dB attenuator and the output amplifier were suspected to be the source of the issue. However, further investigation was required to pinpoint the exact cause of the failure. Therefore, the signal path from the waveform digital-to-analog converter (DAC) to the output was traced.

Block Diagram Analysis

The block diagram of the generator provided valuable insights into its internal components and signal flow. Starting from the output, which included a protection distortion filter and an output amplifier, it was determined that these components could be bypassed depending on the output levels. Two attenuators, namely 10 dB and 20 dB, were also present in the signal path. The suspected relays responsible for the error codes were located at the 20 dB attenuator and the output amplifier.

Examination of Relays and Amplifier Path

To access the internal components of the generator, the cover was removed. The main board revealed the relay placements and their interconnectedness with the amplifier and waveform DAC. Surprisingly, the layout observed in the physical board differed slightly from the diagram provided in the service guide. This discrepancy raised concerns about the compatibility of replacement parts and the accuracy of the troubleshooting steps outlined in the guide.

Checking Power Rails and Waveform DAC

Before delving further into the relay-related issues, it was essential to ensure the power rails were functioning correctly. A comprehensive examination of the power rails revealed no abnormalities, ruling out power-related problems. Attention was then shifted to the waveform DAC, which plays a crucial role in generating the desired waveforms. However, upon checking the output from the waveform DAC, it was discovered that there was no signal present at all.

Clock Signal Investigation

To determine the cause of the absent output signal from the waveform DAC, the clock signal was investigated. The clock divider schematic provided insights into the clock generation process, indicating a differential clock of 200 megahertz. However, upon measurement, it was found that one of the clock lines had a significantly weaker signal compared to the other. This discrepancy led to further examination of the resistors associated with the clock signals.

Resistor Inspection and Replacement

Careful inspection of the resistors revealed discrepancies in their values, which directly affected the clock signal strength and integrity. Suspected resistors were identified by comparing their measured values to the expected 300-ohm resistance. Multiple resistors were found to be faulty, with measured resistances ranging from several kilohms to significantly higher values. These faulty resistors were systematically replaced to restore the proper functioning of the clock signal and potentially resolve the output issue.

Testing the Fixed Generator

After replacing the faulty resistors and ensuring the integrity of the clock signal, the generator was tested to evaluate its functionality. Upon turning on the output, a one-kilohertz waveform with a peak-to-peak amplitude of 100 millivolts was observed. The self-test function was repeatedly executed, and no error codes were encountered, indicating a successful repair. Further tests were conducted to assess the generator's performance at different amplitudes and frequencies, which proved satisfactory.

Conclusion

In conclusion, the troubleshooting and repair of the Keysight 33 250A Function and Arbitrary Waveform Generator proved to be a meticulous process involving careful analysis of the block diagram, examination of relays and the amplifier path, checking power rails and the waveform DAC, investigating clock signals, and inspecting and replacing faulty resistors. The successful repair resulted in a functional generator capable of generating various waveforms.