TSP #89 - Teardown, Repair and Experiments with a Tektronix RSA 6114A Real-Time Spectrum Analyzer

In this episode Shahriar attempts a difficult repair of a Tektronix RSA real-time spectrum analyzer. This well-equipped instrument reports several error messages during startup POST including LO Unlock as well as Signal Path failures. The service manual of the instrument does not provide any detailed block diagram and no schematics. Most failures require the instrument to be serviced by the Tektronix factory. The equipment has various advanced options including 110MHz analysis bandwidth, digital modulation analysis, wide-band IF output and deep memory.
The teardown of the instrument reveals a multi-board, multi-module design. The top of the instrument contains all digital blocks and boards while the bottom of the instrument houses the RF deck assembly. The RF deck is broken into various stages such as attenuator, RF switches, first converter, second converter, IF block, reference synthesizer and LO generator. For the purposes of addressing the YIG problems the LO board is examined. The problem is traced to two components, both dividers in the complex PLL system of the LO subsystem. The LO board is fully analyzed and described and the defective components re replaced.
The repaired instrument is tested for various functionality including DPX, de-modulation and measurement beyond 8GHz CW tones. The instrument passes all self-tests, alignments and detailed diagnostics.
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