In this episode Shahriar repairs an Agilent 8562E 13.2GHz spectrum analyzer which does not power on. Upon pressing the power button the power LED briefly flashes and turns off. Teardown of the unit reveals a compact instrument where the power supply is rather difficult to reach.
The power supply block diagram shows various internal block functions which include startup, DC-DC converter and output regulation stages. In order to diagnose the instrument, the CMOS driver ICs were removed and swamped. An error during the installation of the gate drivers caused a cascade failure of the supply components! After replacing all the affected components as well as the DC-DC converter PWM controller IC, the power supply is repaired.
After powering on the unit it becomes clear that there are several internal self-test and alignment errors. The errors point to YIG oscillator failure. The YIG oscillator no longer has the full range of frequency tuning. The core of the YIG block is replaced with a spare unit from a different Agilent instrument. After re-alignment of the YIG the unit functions correctly. The principle operation of the YIG oscillator is explained and the internals of the defective unit are examined under the microscope.
In this episode Shahriar demonstrates the capabilities and features of the Carbide 3D Nomad 883 Pro CNC machine. The primary interest is for PCB milling and therefore the machine’s accuracy, speed and software capabilities are examined. The Nomad 883 Pro offers an Aluminum chassis design with a custom machined spindle. XYZ movements are supported by linear bearings with a resolutions of 0.0005 inches and a reputability of 0.0015 inches. Furthermore the Nomad has an accuracy of 0.005 inches. Unfortunately the spindle speed is limited to 10,000 RPM which lags behind other competing CNC machines such as the Bantam Tools Pro (formally Othermill Pro) which support up to 26,000 RPM.
In order to push the machine to its limits, a benchmark PCB design is milled with features smaller than 10 mils. The result shows that the PCB flatness is critical for achieving such fine features since the Nomad does not currently offer mapping features. All milling is done in a custom-made oil bath which must be used for FR-4 materials due to dangerous glass-dust generation during milling.
In this episode Shahriar repairs an Agilent PSA Series Spectrum Analyzer. The instrument generates many errors during self-alignment and produces no measurements below 3.2GHz. The block diagram of the unit is thoroughly presented and various possible failure points are considered. Based on the observation of the noise floor, the most likely cause is the second LO module. The measurement of the LO power indicates that the second LO power is fall below nominal.
The second LO signal (at 3.6GHz) is generated by a DRO PLL module which is locked to 600MHz. The PLL is functional, however the output power is below -20dBm. Teardown of the module reveals a simple design with a doubler and filter. The filter (which is discolored) shows a huge loss likely caused by RF losses due to trace degradation. Thinning the traces provides some improvement and the remaining loss is compensated with a two stage RF amplifier. With this modifications, the instrument’s alignment errors are partially resolved.
The next problem is with the input attenuator at the 20dB range. This problem is simply resolved by providing lubrication on the attenuator solenoids after disassembly. The instrument is then used for various measurements to verify its correct operation.
In this episode Shahriar investigates the noise generated from the DPH3205 Buck-Boost DC/DC Converter Module. This module is part of a family of affordable devices which can be purchased online. The particular model (DPH3205) shown in this video can be purchased from here. The Keysight S-Scope in conjunction with the N7020 power probe is used to measure the noise behavior of the circuit. It can be observed that the module produces many harmonics of noise spanning up to and beyond 1MHz.
A power operational amplifier is used in conjunction with a 4V Zener diode to produce a crude voltage follower. The PSRR of the operational amplifier can filter the noise from the DC/DC converter. This is verified by measuring the noise coming from the operational amplifier. The noise is significantly reduced. This circuit is not entirely practical and is used for demonstration purposes only.
In this episode Shahriar repairs an Anritsu MS9710B Optical Spectrum Analyzer. The instrument intermittently does not boot and when it does it generates a Grating Mirror error. Some investigation reveals that the problems may simply be poor internal cabling connections which can be resolved by cleaning all connectors and re-building the unit. The LCD screen’s CCFL have also failed. An LED back-light replacement provides the screen with a vibrant and bright colors.
The unit is very compact (which is unusual for an Optical Spectrum Analyzer) and makes it ideal for bench-top working environments. The broad-spectrum built-in reference laser can be used to calibrate and align the instrument which proves to work perfectly. After calibration, a laser diode from an Agilent Lightwave Transmitter is measured. Interestingly it can be seen that the unit produces two tones at ~1nm apart which indicates the laser operates in two modes. A very interesting result given that the wavelength meter only reports one tone at the average wavelength of the two modes.
The Signal Path (TSP) is an electrical engineering video blog for industry professionals, students and hobbyists. TSP is a non-for-profit website dedicated to provide free education spanning a wide range of electrical engineering topics. Equipment reviews, tutorials and repair videos are posted regularly.