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HP8753D Test 53 Sampler Magnitude and Phase Correction Constants fails

Question asked by mankan on Dec 1, 2019
Latest reply on Mar 24, 2020 by BurntChips

Hi all,


after finally upgrading the FW to v6.14 my HP8753D with 6GHz option I'm now running thru the adjustment tests.

I have test 44 (Source Default Correction Constants), 45 (Source Pretune Default), 46(Analog Bus), 48(Source Pretune), 52(ADC offset), 47(RF Output Power), 51(IF Amplifier), and 54(Cavity Oscillator Frequency) running successfully. Also tests 21/22 (Operators Check Port 1/2) works fine.


But test 53 fails quite early, it says LO 30MHz on screen a while and then it disappears and I get the fail message. The screen looks like this:


Not sure if that gives any clues or not.


So I have tried to do the Poke commands correction and rerun the tests, still fails at the same place. And I have also started following the diagnostics instructions and so my next step was the do the "Check the A and B inputs" and the look on the sloping curve looks like the good picture but I get a 2dB scale instead so it starts at around 3dB and slopes down to -4dB compared to the service manual picture that shows 1.5dB down to around -2dB.


So that got me running test 18 (ADC offset) 17 (ADC linearity), and then  A12 reference check, A13/A14 Fractional-N all successful. So additional tests would be "Check the 4MHz REF signal", "A7 Pulse Generator Check" and "A14 VCO Range Check with Oscilloscope", right?


But before I put the 8753 on the bench and open it up again I'd like to know what am I actually chasing? How bad is it that test 53 fails? Something serious or will it be calibrated away anyway or what kind measurements could suffer from this? Could it be something completely else that is wrong? Should I go find out what causes the steeper A and B input slope instead?


A complicating factor is also that there is no complete service manual for the 8753D. The ones I've used are for 8753D Option 11 which uses different test setups and the PDF also have most figures missing. So one has to gather information from 8753E and ES/ET guide as well as the 8753D FW upgrade instructions and do assumptions in some cases that D version behaves the same as E/ES/ET.


Anyway, any input to this is much appreciated.


Thanks in advance

Marcus, SA5PMG