In this episode Shahriar repairs an Agilent 54845A oscilloscope with an intermittent failure. The instrument occasionally fails self-calibration and the displayed waveform shows undesired spurious activities. The teardown of the instrument reveals customized front-end section coupled into a ceramic-substrate ADC ASIC designed by Agilent. The packaged ADCs are placed in sockets. The ICs are removed and the ceramic carrier is cleaned; this resolves the intermittent problem with the channels. The architecture of the scope is also presented. The functionality of the scope is verified through self-calibration, self-test and measurement of various waveform.
Tag Archive for Analog
In this episode Shahriar repairs an Agilent E7495B 2.7GHz base-station test set capable of VSWR measurements as well as spectrum analysis. This particular unit is well equipped with many options however does not power on. A full teardown of the instrument reveals a faulty DC power conditioning module. The input filtering capacitor has failed. After component replacement, the unit is re-assembled. The functionality of the instrument is verified as well as a few quick experiments demonstrating various options.
In this short episode Shahriar upgrades the recently repaired Fluke PM6680B with a new OCXO design by Dan Watson. The design of the module is examined as well various considerations for providing ultra clean 10MHz reference for instrumentation. After module installation the unit functionality is verified. More information about the module is available here and here.
In this episode Shahriar reviews the Keysight N7020A 2.0GHz Power Rail Probe. This power rail probe boasts the following features:
- Low noise: 1:1 attenuation ratio probe adds only 10% to the baseline noise of the oscilloscope it is attached to.
- Large offset range: Has a large +/-24 V offset range, enabling users to set their oscilloscope at maximum sensitivity and have the signal centered on the screen.
- Low DC loading: 50 kΩ DC input impedance will not significantly load DC power rails.
- Large active signal range: Has a +/-850 mV active signal range in addition to its large offset range so users can measure large transitions of their power rails.
- High bandwidth: 2-GHz bandwidth makes it very useful for finding high-speed transients that can have detrimental effects on clocks and digital data.
After a brief presentation about the benefits of the N7020A, the probe and probe accessories are examined. The probe’s capability to provide up to +/-24V of offset is demonstrated and the input impedance at DC is measured. The probe is then used in conjunction with a Xilinx FPGA board to characterize a broadband power supply noise issue.
In this episode Shahriar examines a faulty Fluke PM6303A Automatic RCL Meter. This unit power on however reports the incorrect measured value for all components. The instrument also does not provide the built-in 2V bias. After a quick teardown of the unit, physical damage to several input resistors can be observed. It becomes clear that a high-voltage discharge has caused a cascade failure of several components on the input signal path. These faults are traced to a chain of protection Zener diodes, resistors and general purpose diodes. After all the components have been replaced, the unit’s functionality is restored.
The schematic and block diagram of the unit is also presented and the principle of operation is explained. The repaired instrument is then used to measure several components to verify is functionality.