In this episode Shahriar reviews the Siglent SDM3055A 5.5-Digit Multimeter. After a brief look at the instrument’s datasheet, a full teardown is presented. The instrument utilizes a two-board design and a large LCD screen. The SDM3055A provides a comprehensive set of measurements including capacitance as well as various graphing capabilities including histogram, trend and bar graphs. USB and LAN connections are standard and a USB-GPIB can also be purchased. The performance of the instrument is verified through experiments with various functions and setups.
Archive for July 20, 2015
In this episode Shahriar repairs a Stanford Research Systems Model PS350 5000V-25W High Voltage Power Supply. The unit continuously displays 2.5kV without the output being enabled and produces no output voltage. Verification of power supply voltages reveals the issue is linked to a disconnected 15V voltage regulator IC. After the repair, the output voltage is verified with both positive and negative outputs. The principle operation of the instrument as well as the Cockroft-Walton high voltage generator is reviewed.
In this episode Shahriar investigates a faulty Agilent E3631A 80W triple output power supply. The instrument powers on, display a fully illuminated VFD display before a long beep and dark screen. The disassembled unit reveals a two board construction. After an unfortunate finger burning experience, the fault is traced to pair of extremely hot voltage regulators and Zener diodes. The temperature of these components is measured using a thermal camera and reach 400C! The schematic of the power supply is examined and the appropriate components are replaced. The performance of the unit is verified after the repair.
In this episode Shahriar examines the failure of a Siglent SHS810 100MHz 1GS/s portable oscilloscope and multimeter. The instrument’s multimeter inputs are functional, however the neither of the oscilloscope inputs display the correct waveform. The displayed signal varied largely as soon as a coax cable is connected and the instrument is powered from an external signal source. This hints to a grounding problem. Further examination of the probes also shows large damage to the ground pads from a possible high-voltage short circuits through the shared ground between the scope inputs.
The disassembly of the unit reveals heavy damage to the ground PCB traces of the input channels. After thorough cleanup of the PCB, the ground traces are repaired using copper tape. The new ground plane corrects the problem and the scope can now be used to measure RF signals correctly.