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Re: HP Agilent 8753ES VNA repair [Help]


 

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There are contradictions in the test results:

If you say that the VCO frequencies are correct (39.996MHz for LOW and 39.84Mz for HIGH), then this necessarily means that the VCXO is at precisely 40 MHz, that the divider L=4kHz and H=160kHz are functional, that the PLL is working, that the VCO output to the mixer correctly converts the signal to L=4kHz and H=160kHz, that the PLL loop is closed and stable. But the divider by 40 could be faulty if you don't have always 996kHz for HIGH at PIN2.

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You say you don't have the correct 4KHz or 160KHz at output divider (909 KHz output instead of 160 KHz).

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My error TP14, 10.4MHz it’s not good, its 10.004MHz. Marker was OK , added text have error on picture.

You have 10.4MHz to TP14 for 10MHz setup, it’s bad.

In this case A14 have problem if TP20 have for high band VCO must be 39.84Mz and VCO at 39.996MHz for lowband <16MHz.

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Need to know if the frequencies are OK for TP20.

I'll look at all that again tomorrow.

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Yves

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