TSP #209 – Teardown, Repair & Analysis of an Agilent 83752A 10MHz – 20GHz RF Synthesized Sweeper

In this episode Shahriar takes a close look at an HP 83752A which shows no signs of life. The power supply of the instrument does not produce standby or any other output voltages. The power supply is examined and the startup circuitry is at fault. The problem is traced to a bad startup capacitor for the primary PWM controller. A replacement resolves the issue and the instrument powers on.
The instrument however has other issues. An UNLOCK condition is displayed and further testing shows that the frequency output of the instrument below 2GHz is unstable. The overall block diagram of the unit is presented and the fault is logically traced to a potential problem with the reference 100MHz of the hetrodyne block. An X-Ray of the board allows us to reverse engineer the final output amplifier and a faulty NPN is located. A replacement resolves the UNLOCK condition and the instrument is fully functional.

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