The network analyzer is missing the main HDD which initially prevents it from being tested. An image from a donor E5701C instrument is used to boot the unit and gain access to the instrument firmware. The unit shows an inaccurate S11 with an open Port 1 while S22 shows a perfect reflection. This indicates a potential problem with the Port 1 T/R module. Teardown of the module reveals catastrophic damage to the resistive front-end coupler which has been mostly likely caused by a large RF input power incident. After cleaning the PCB area, a replacement coupler is constructed. The repaired unit is checked for full self-test and used to measure a YIG tuneable filter.
You can may check the Andostar microscope lineup here. (Direct Link / Not-tracked)
More information about Wheatstone Bridge can be found here.
In this episode Shahriar repairs a Noise-XT 2MHz – 7GHz Ultra-Low Phase-Noise Clock Synthesizer. The instrument’s history indicates that it has suffered a fall from a work table. After a lot of difficulty, the instrument control software was found so that the unit can be tested.
Initial tests reveal that a very small output is present, however nearly 40dB below the desired value. The unit teardown shows an architecture based on dual Analog Devices DDS 14-bits DACs in conjunction with a Z-COMM VCO and a series of dividers & frequency multipliers. A detailed analysis of the unit is presented.
RF and analog measurements indicate that the RF connector is not making adequate contact with the final trace of the RF output. This explains the low output power. This problem is resolved by replacing the SMA connector entirely. The device output power, frequency accuracy, stability as well as cross-correlation phase-noise measurements are presented.
The instrument does provide an RF output signal. However, there is also a large DC offset voltage present at the output RF port which changes depending the frequency band. The DC voltage is present even when the output RF signal is disabled. Furthermore, the OCXO of the instrument is defective and does not produce a 10MHz output signal.
The block diagram of the PSG is examined in details with emphasis on the final attenuator, coupler and doubler RF decks. Interestingly enough the output offset is traced all the way back to the Modulator Filter block. The teardown of the module reveals a series of PIN diode switches and after some investigation the fault is traced to a damaged PIN diode on the sub-3.2GHz path. Since the diode can’t be easily replaced, the control voltage to the diode is disabled instead which removed the DC offset problem.
The OCXO teardown reveals that during a prior repair, the oscillator module has been damages and torn off the PCB. New pins are added to the oscillator module which returns the crystal back to working condition. The performance of the PSG is verified using a spectrum analyzer and frequency counter.
In this episode Shahriar takes a look at a malfunctioning Agilent N9020A MXA. This instrument was provided by AllTest who hold the largest inventory of used and refurbished instruments. They have trusted The Signal Path to attempt a repair on the instrument and to support the educational content of this channel. Thank you AllTest! Please visit their website for all your measurement, calibration and service needs:
The instrument fails RF Alignment despite the fact that all calibration signals are present and can be viewed on the unit. The front-end attenuators also appear to be fully functioning. A full sweep of the input shows that the instrument fails to make measurements between 8.4GH – 14GHz as well as above 17GHz. The block diagram is analyzed and the likely fault is traced to a doubler circuit on the A13 RF Assembly. The teardown of the assembly along with step-by-step reverse engineering is presented. An X-Ray of the module also reveals the hidden band-pass filter structure on the PCB. Various dies are also examined under the microscope. The A13 module is replaced with which corrects all the instrument faults and returns the unit to normal operation.
In this episode Shahriar investigates the failure of a Voltech PM3000A 3-Phase Universal Power Analyzer. This instrument is capable of advanced measurements on power profile and performance of a DUT. The unit shows “Voltage & Current OVERLOAD” condition on all channels even without a DUT connected.
The teardown of the unit reveals the isolation techniques used between the analog sampling heads and the main digital/DSP board. The instrument uses a combination of transformers and optocouplers to provide power to the sampling heads and receive digitized data from the voltage/current ADCs.
Close examination of the unit shows a faulty capacitor on the AC power supply feeding the sampling heads. The capacitor is replaced which corrects the overload condition. The unit is then used to measure the power profile of a simple glue-gun. The PF and THD measurements show that the glue-gun is equipped with a triac for power control; an expected result for a simple glue-gun.
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.