Hi Roberto,
Check your e-mail.
Vladan
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--- In hp_agilent_equipment@..., "roberto.barrios" <rbarrioss@...> wrote:
Hello,
I am trying to fix a 71100A spectrum analyzer and I'm stuck. It passes the "analyzer test" built into the firmware but does not pass calibration of the resolution bandwidth for some of the bandwidth filters (in the 70902A IF module).
The problen is easily seen in the shape of the curve from the calibrator, which for three of the filters does not look like it should. If you take a look at
you will see that:
* 10 Hz: Looks like if it was composed of two filters in series not aligned to the same center frequency. Peak amplitude 8 dB down.
* 30 Hz: Almost right but again not 100% symmetric. Peak amplitude OK.
* 100 Hz: Seems nice to me.
* 300 Hz: Just A bit asymmetric
* 1.00 kHz: Ugly, centered but no simmetry. Peak amplitude OK.
* 3.00 kHz: Ugliest, a complete mess. Peak amplitude 13dB up.
* 30.0 kHz: Looks nice.
* 100 kHz: Strange shape, convex skirts instead of concave (??)
* 300 kHz: Strange shape, convex skirts instead of concave (??)
The first error ( 2023 , Illegal Cal Signal ) appears when the 3.0 kHz test is done. The last one ( 6011 , RBW hardware error ) appears after the last one, which is the 10Hz test.
I have the Component Level Information Package (from ARTEKMANUALS) for the module, and it shows there are (among other), 9 filter stages:
LC1 > LC2 > XTAL1 > XTAL2 > XTAL3 > XTAL4 > XTAL5 > LC3 > LC4
Most of the stages have a bandwidth and center control pot/cap, some also a symmetry control. I tweaked them and could not see any significant difference in the ones that don't look nice so I carefully left them all where they were.
There are also "SHORT" LEDs on each filter stage, I believe to signal which stages are being bypassed. What I do not understand is why the LC1, LC2, LC3 and LC4 LEDs are never ON and the XTAL1, XTAL2, XTAL3, XTAL4 and XTAL5 are either ON
of OFF, all at the same time. From 10K up they are all ON and from 3K and down they are all OFF. I was expecting some kind of weighted switching to get the desired filter bandwidth, so I could find and repair the stage that was failing, but it does not seem to be that easy. Since it is possible to have continuos bandwidth control, some of the stages are probably not as simple as I thought.
Appart from some of the trim caps being stuck, there was no physical damage that I could find.
Does anyone know how the filter stages work? Suggestions to try?
Thank you and Merry xmas to you all.
Roberto EB4EQA
