TNP #20 – Teardown, Repair & Experiments with Stanford Research Systems SR830 DSP Lock-in Amplifier

In this episode Shahriar takes a look at a SRS SR830 DSP Lock-in amplifier. The repair of the instrument is fairly simple and provides a quick look at the internal construction of the unit.
The instrument is then used for characterizing nonlinearities of a pair of matched diodes in large-signal operation. A Tektronix 4-Series is also used alongside the SR830 in DDC mode to show the harmonic behavior of the DUT in frequency domain. The SR830 is able to discern extremely small variation in temperature between the diodes and the resultant 2nd order harmonic changes in both amplitude & phase.​​​

TSP #210 – Going off-grid! BigBattery RHINO 48V, 14kWh LiFePO4 Battery Review & Experiments

In this episode Shahriar takes The Signal Path Lab off-grid! The BigBattery RHINO 48V LiFePO4, 276Ah, 14kWh is combined with a Growatt SPF 6000T inverter to provide 240V split-phase power to the house.

You can see the kit used in this video using this untracked, direct link to

The review of the battery is organized as follows:

00:00 – Introductions & considerations.
01:33 – BigBattery offerings, battery configurations, battery chemistry, specifications, warranty, etc.
05:51 – Battery construction quality, connector & fuse design, mobile cart, attachment options.
07:50 – Provided battery cable with Anderson connector, ratings, quality.
08:14 – Built-in LCD screen, GUI & BMS access from the battery, phone app & BMS configuration.
11:36 – Battery protection, BMS under small loads, BMS disconnect behavior, power reporting.
16:08 – Off-grid setup, Growatt inverter wiring & interfaces, transfer switch & AC access.
18:28 – Benefits of a boiler setup for battery backup operation.
18:59 – Ensuring correct earth-ground & neutral wiring of the backup system.
19:52 – Going off-grid! House power measurements, battery discharge behavior.
21:27 – Battery charging behavior, balancing, charging battery to maximum level, charge waveform.
22:44 – Concluding remarks.​​​

TSP #209 – Teardown, Repair & Analysis of an Agilent 83752A 10MHz – 20GHz RF Synthesized Sweeper

In this episode Shahriar takes a close look at an HP 83752A which shows no signs of life. The power supply of the instrument does not produce standby or any other output voltages. The power supply is examined and the startup circuitry is at fault. The problem is traced to a bad startup capacitor for the primary PWM controller. A replacement resolves the issue and the instrument powers on.
The instrument however has other issues. An UNLOCK condition is displayed and further testing shows that the frequency output of the instrument below 2GHz is unstable. The overall block diagram of the unit is presented and the fault is logically traced to a potential problem with the reference 100MHz of the hetrodyne block. An X-Ray of the board allows us to reverse engineer the final output amplifier and a faulty NPN is located. A replacement resolves the UNLOCK condition and the instrument is fully functional.​​​

TNP #19 – Teardown & Repair of a Keysight U1253B 50,000 Count True RMS OLED Handheld Multimeter

In this episode Shahriar takes a look a Keysight U1253B multimeter with a notorious problem of failed OLED screens. The OLED would degrade and stop working on some of these units. Since the original OLED model is almost impossible to find, replacement OLED would require a protocol translation layer. The replacement module uses an FPGA to achieve this.

The teardown of the unit as well as the repaired units are shown. The performance of the instrument is verified using a universal source and an 8.5-digit multimeter.​​​

TNP #18 – Repair & Analysis of a W-Band (75-110GHz) WR-10 12dBm Power Amplifier Module

In this episode Shahriar takes a look at a non-functional W-Band (75-110GHz) power amplifier module with WR-10 waveguide ports. A quick inspection reveals a broken DC connector which can be easily repaired. Since a W-Band VNA or source is not available, the amplifier’s excess noise is instead measured using an external mixer and a Keysight MXA-B. The noise power spectral density shows the the amplifier is likely functional with the expected noise and gain.​​​