In this episode Shahriar investigates the failure of a GW Instek 1080W power supply capable of providing up to 80V and 40A of programmable output voltage and current respectively. The power supply does not power on. However, relay noises can be heard inside the instrument during power on.
Teardown of the unit reveals a modular design with PCBs on all sides. The instrument comprises 6 different modules and 3 complete power supplies in parallel. The controller circuit is powered from the middle power supply module. Examination of the boards reveals three separate failed devices. The in-rush power resistor which prevents the main supply board from startup, a damaged MOS power transistor on the supply output and surface mount resistors. All components are replaced. The instrument’s performance is verified with a BK Precision 8601 electronic load.
In this episode Shahriar investigates the failure of an Anritsu MS2712B 1.7GHz portable spectrum analyzer with built-in tracking generator. The instrument is missing the main firmware flash card which is easily replaced. A full teardown of the instrument is presented with focus on both the tracking generator PCB and main RF deck. Various ASICs and microwave components are closely examined. To help with removing and replacing many microwave screws, a Hitachi/Metabo electric screwdriver is used which can be purchased here.
After re-assembly of the unit, it becomes apparent that a mechanical push on the RF deck causes the LO1 PLL to unlock. This points to a fault in one of the microwave components. The issue is traced to a broken solder joint inside of the VCO modules. After repair, the instrument functions normally. The performance and tracking generator functionality is verified by measuring a tuneable band-pass filter.
In this two-part episode Shahriar repairs an Agilent N5230A 13.5GHz PNA-L which suffers from un-leveled output in full frequency sweep range. The instrument is not able to produce any outputs above -25dBm above 10.5GHz and shows below specification output power levels below 10.5GHz.
Teardown of the unit reveals various microwave modules with the SSLAM final module responsible for amplitude leveling and frequency multiplication for frequencies above 10.5GHz. Teardown of this module shows a collection of MMIC dies wirebonded together using micro-strip ceramic pieces and interconnects. MMIC include switches, amplifiers, filters, multipliers, power detectors and attenuators. After examining the input/output signals of the module it becomes clear that the input switch IC is damaged. Unfortunately, an attempt to replace the die with a packaged QFN GaAs device fails. However, a lucky eBay find of a used SSLAM module saves the day and the instrument is restored to full functionality. Some measurements of an packaged evaluation board of a GaAs IC is demonstrated using the newly repaired PNA-L.
In this episode Shahriar analyzes the failure of two Agilent 8449B Preamplifiers. These units should provide up to 30dBm of gain from 1.0GHz to 26.5GHz intended for use as a preamplifier. Both amplifiers test positive for power supply voltages and operation. After removing the interface cables from the amplifier module to the front panel, it becomes clear that mechanical shock has caused damage to the front panel connectors. Replacement cables and connectors are used to correct the problem.
In this episode Shahriar repairs an Agilent 4338B milliohmmeter. This instrument is capable of measuring extremely small resistances down to 10uΩ while maintaining a DUT voltage of less than 20mV. The instrument powers on with the message ADC Failure. Investigation reveals that the instrument uses an obsolete ADC which must be removed from the board in order to reverse engineer its operation. While the ADC turns out to be functional, a PAL device which controls the ADC timing is faulty. A new device is salvaged from a donor board to complete the repair. The instrument is then used to measure several small known resistances.
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.