In this quick episode Shahriar performs some regular lab maintenance. Two instrument need attention. The Agilent 3458A is reporting a Nonvolatile Memory Error & and the Agilent MSO9404A is reporting a dead CMOS battery.
Both problems are easily addressed by changing the battery backup. In the case of the 3458A, the calibration content has to be re-programed into the new NVRAM ICs.
In this episode Shahriar repairs an Agilent N5182A MXG Vector Signal Generator. The instrument produces the correct output signal for some set frequencies but reports a Fractional-N Unlock error for others while the output signal completely disappears. The instrument also fails many self-test checks.
The block diagram of the unit is described in details with a measurement strategy to analyze every element of the PLL loop. The band-pass filter banks are isolated and measured with a Siglent network analyzer and are shown to be fully functional. The VCO output amplifiers & doubler are also fully functional and tested using a Siglent spectrum analyzer. The PLL loop is then "overwritten" and manually adjusting the VCO control voltage demonstrates that the oscillator can cover its entire designed tuning range. The fractional-N divider also appears functional for the appropriate input frequency ranges. Finally, although the GaAs phase detector appear functional, it is possible for such a component to slowly degrade where the phase detection gain changes significantly. This custom Agilent part is sourced from a donor board and the instrument now functions across all frequency ranges and passes all self-tests.
The phase noise performance of the unit is verified against the datasheet using an Agilent E5052B signal analyzer with cross-correlation capability.
The Signal Path (TSP) is a science & electrical engineering video blog for industry professionals, researchers & students. TSP is a not-for-profit website dedicated to provide free education spanning a wide range of electrical engineering & science topics. Equipment reviews, tutorials and repair videos are posted regularly.
