In this episode Shahriar explores the cause of failure of an Agilent E4405B ESA 13.5GHz spectrum analyzer. In a previous episode, an E4407B version of the ESA was repaired and upgraded which is helpful in debugging and analyzing this instrument. The instrument displays LO Unlock which is a familiar problem. After an overview of the system block diagram, the LO signal path is traced and analyzed for problems.
After some investigation, the problem appears to be identical to the E4407B model repaired before! The Hittite (Analog Devices) divide-by-4 static divider unit has failed and does not divide correctly at high frequencies. The component is replaced which restores the instrument’s functionality.
The LCD screen of the unit is also very dim. The CCFL tube and the inverter are replaced with an LED back light instead. The unit then produces a bright and vibrant graphs and text. The performance of the instrument is verified with a Keysight MXG signal generator.
In this episode Shahriar & Rosanah investigate an Agilent power supply which does not appear to power on. It can be quickly observed that the fuse has failed on the unit. Using an isolation transformer a small amount of AC voltage is applied to the unit after the fuse replacement. It is clear that a short is present somewhere in the instrument since even at 10V AC the instrument consumes more than 1A.
After separating the internal transformer from the main PCB, the high current consumption is eliminated. The short is traced to a damaged main rectifier in the instrument. A replacement rectifier is used which allows the instrument to power on.
The VFD display is however extremely dim. After a failed attempt at restoring the VFD brightness, a new display is purchased from eBay. The replacement produces a bright vibrant VFD display. The performance of the power supply is verified under load.
In this episode Shahriar repair a Fluke PM6685R Rubidium Frequency Counter. The instrument shows highly unstable results and produces high-pitch noise when powered on. The high-frequency noises point to a problem with the DC-DC converter circuit in the power supply module. A close examination points to degraded capacitors. After all capacitors have been replaced, the noise issue is resolved. The instrument’s performance is then verified and calibrated against an external Rubidium reference. The agreement between the units is better than 10ppb.
In this short episode Shahriar investigates the failure cause of a Keithley 2400 SMU. The unit powers on and responds to controls however produces no output signal. Further examination reveals that the VFD display shows no activity when the output is enabled; normally the measured output voltage and current are displayed. This failure points to a digital problem, potentially a failure in the analog board FPGA.
Upon close inspection the FPGA clocking circuitry appears to have a failed solder-joint. A quick re-flow of the affected part corrects the problem and the unit reports the appropriate readings. The unit is then upgraded to the latest firmware and calibrated using a Keithley 7510 DMM.
In this short episode Shahriar repairs a more affordable instrument! This BK Precision LCR meter does not power up despite looking almost new. The teardown of the unit reveals several damaged components. Without any schematic and obscure part numbers some circuit configurations have to be reverse engineered. One of the main failed components is a TI DC-DC converter IC whose datahseet is examined during the repair.
The damaged components are replaced and the unit powers on normally. The performance of the instrument is verified using a HP LCR meter. The demonstrated Soldering Iron Stand can be found here.
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.