TSP

In this episode Shahriar takes a look at a faulty SRS DS360 ultra-low distortion function generator. This instrument is capable of producing pure sinusoids with better than -110dB of THD!
Although the unit powers on, changing the frequency or output signal does not result in any internal relay switching and the instrument does not produce any output signal.
The block diagram of the instrument as well as the theory of operation is described before the teardown. The teardown also shows the two board design and the interface between the digital/analog boards. The fault is finally traced to a broken optoisolator IC between the two boards. Without this interface IC none of the configuration parameters from the digital board arrive to the analog subsection. The faulty part is replaced and the unit is restored. The difficult measurement of the THD is also presented using an SRS SR830 DSP lock-in amplifier.

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