In this episode Shahriar takes a look at (unusually expensive) Sencore PA-81. This non-functioning unit behaves strangely across all ranges. Furthermore, the left and right channels do not produce the same output measurements.
Teardown of the unit shows the overall architecture of the instrument. Closer examination of the service manual also shows the schematics and the design of the front-end auto-ranging circuit. The unit has been powered with an external power supply at a higher voltage than the specific input range. Multiple relays as well as the driving bipolar transistors have been damaged and must be replaced.
After the repair the unit is used to measure several signal levels. The isolated analog outputs are also characterized for gain balance and linearity.
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