Teardown & Repair of an Agilent E8257D 250kHz - 31.8GHz PSG Analog Signal Gen.

[Hugoneus]

In this episode Shahriar repairs an Agilent E8257D PSG Analog Signal Generator generously loaned by AllTest. The instrument does provide an RF output signal. However, there is also a large DC offset voltage present at the output RF port which changes depending the frequency band. The DC voltage is present even when the output RF signal is disabled. Furthermore, the OCXO of the instrument is defective and does not produce a 10MHz output signal.

The block diagram of the PSG is examined in details with emphasis on the final attenuator, coupler and doubler RF decks. Interestingly enough the output offset is traced all the way back to the Modulator Filter block. The teardown of the module reveals a series of PIN diode switches and after some investigation the fault is traced to a damaged PIN diode on the sub-3.2GHz path. Since the diode can't be easily replaced, the control voltage to the diode is disabled instead which removed the DC offset problem.

The OCXO teardown reveals that during a prior repair, the oscillator module has been damages and torn off the PCB. New pins are added to the oscillator module which returns the crystal back to working condition. The performance of the PSG is verified using a spectrum analyzer and frequency counter.

You can watch the video here: [40 Minutes]
youtu.be/GaaA46r7DUk

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[BFX]

This is the level of repair knowledge what I'm ready to pay
Now I'm Patreon and I will increase my donations by level of repair
 Thank you  Hugoneus. I wish you even better cooperation with alltest, I think they will catch you soon

[Hugoneus]

This is the level of repair knowledge what I'm ready to pay
Now I'm Patreon and I will increase my donations by level of repair
 Thank you  Hugoneus. I wish you even better cooperation with alltest, I think they will catch you soon

Thank you. Much appreciated.

[vaualbus]

Finally I see inside one of this machine! I would really enjoy a teardown of the different boards, but the way this instrument use a lot of the board used in the ESG series of signal generator that you had already repairs in the past (but I think the base model is the Ghz version as the Frac-N, Sampler board are the same) I realize this by comparing the two block diagrams.
And of course they had completly different RF section as this instrument can reach up to 67Ghz so amplifier and RF loop is different but I'm pretty sure that the stuff before the YIG is very similar to the base ESG generators.
Any way good video as always and I wish you can enjoy the quarantine by making more video!