In this episode Shahriar diagnoses a malfunctioning Agilent 86118A 70GHz Dual Remote Sampling Head. With 70GHz of analog bandwidth per channel, this module definitely deserves a repair.
Unfortunately most failed remote-head modules aren’t repairable if the damage is in the sensitive proprietary III/V front-end IC. However, in this situation the module intermittently fails calibration which is more promising. The teardown reveals the architecture of the module from the point of view of the analog and strobe paths. Measurements on the strobe path also show a potential failure on the power-amplifier/splitter network which feeds the two remote-heads. A pair of transistors are replaced on the strobe path which correct the problem. The unit passes calibration and is then used for various eye-diagram measurements to verify full functionality.
In this episode Shahriar investigates a failed Rohde & Schwarz AFQ100A I/Q (ARB) Modulation Generator. This instrument provide differential I/Q outputs with exceptional SFDR which makes it ideal for various wireless system testing. The instrument shows a stand-by LED but does not power on.
The problem is tracked to the main power supply’s soft power-on circuit. After the repair of the power supply, it becomes clear that the main HDD is also defective. An identical donor drive is used to repair the broken HDD main controller board. A full teardown of the instrument is also presented. After the repair, the instrument is used to generate various arbitrary waveforms for performance verification.
In this episode Shahriar attempts to repair a Fluke Documenting Process Calibrator. The device does not power on with neither a battery nor an external power supply. Although the schematic of this particular instrument is not available, an older model schematic shares many of the design aspects. After close examination of the circuit and various testing of power supply sub-circuit, real-time clock and main processor, it becomes clear that the problem is with a corrupt firmware. The repair is put on hold until a firmware upload method is determined.
After some help from the community, a new firmware has been found and can be uploaded into the instrument. By forcing the processor into a bootloader mode, the firmware update can happen even if the original firmware is corrupted. After the firmware fix, the instrument is tested for various functionality include DC/AC/I/Resistance calibration and measurement modes.
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 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.