TSP #197 - Teardown, Repair & Analysis of a Rohde & Schwarz FSL 9kHz - 6GHz Spectrum Analyzer

In this episode Shahriar investigates a failed R&S FSL Spectrum Analyzer. The instrument shows an unusual spectrum trace and fails a wide range of self-test functions. The LO Unlock failure is likely the most important item to address which can cause a cascade failure of other functions. The teardown of the instrument shows a single-board RF design. The system architecture is analyzed along with an X-Ray of the main board showing various RF/LO routes and interconnects. The core synthesizer is examined and measured along the signal path to verify the operation of each part. The failure is traced to an open 1-Ohm resistor which feeds the power supply of the divider IC feeding the PFD of the PLL. A ceramic capacitor failure is also observed which may explain the damage to the 1-Ohm resistor. After these components are replaced the instrument passes all self-tests. The functionality of the instrument is verified by measuring tones from 9KHz - 6GHz using a Keysight MXG.