In this episode Shahriar takes a look at a R&S SMBV100A Vector Signal Generator which does not produce the correct output level. Despite passing all self-tests and ALC checks, the output power level is far below expectation. The output also shows a high-pass frequency response.
The (heavily simplified) block diagram of the instrument is examined and discussed. The teardown of the unit reveals the output RF board which is presented in details. Since the instrument cannot detect the failure internally, it is very likely that the fault is part of the RPP output RF relay. The circuitry as well as the datasheet of the components are examined. Measurements show that the output RF relay is never activated due to a faulty PMOS transistor. After transistor is replaced, the unit shows the correct output level. The baseband generator functionality is also verified.
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.
In this episode Shahriar reviews another SAF Spectrum Contact. This model covers the Ka-Band (24GHz-40GHz), intended for 5G mm-Wave field measurements. The K-Band unit offers additional functionality such as 10MHz minimum span as well as RBW/VBW control down to 100kHz.
The teardown of the instrument reveals a similar architecture to the previously reviewed V-Band unit. Various system components are analyzed and explained. Some of the instrument’s GUI capabilities are also presented.
For experiments, a 900-element 38GHz planer array antenna is used at a distance of 2.5 meters. A slow-FM modulated RF signal centered at 38GHz is generated and measured which allows for the antenna gain characterization as well as exploration of the instrument’s capabilities.
In this episode Shahriar repairs a malfunctioning Agilent N5182A MXG Vector Signal Generator. While the instrument operates perfectly above 250MHz, below 250MHz the output is very low with a significant increase in the noise floor.
The block diagram of the synthesizer is presented showing various RF signal paths. It is shown that the sub-250MHz band is derived from a hetrodyne section which is where the problem located. Using a EM probe, various signal flows are discovered on the main board and compared with the block diagram. The main problem is traced to a doubler circuit which generates a 1-GHz LO signal for the hetrodyne section. The doubler comprises a transformer coupled to a dual diode surface mount IC. The IC is replaces which restores the doubler functionality and repairs the instrument.
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.