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Mostly working HP 8559A, but the display reads 2/5 the real freq

Question asked by robstoddard on May 5, 2014
I have a mostly-working spectrum analyzer here, but the frequency on the main display reads 2/5 of what it should above 1 MHz.  Below `1 MHz, it reads as if I'd set the Freq Span **** to 100 MHz.  The scales are pretty much the same too, at 100 kHz it reads the same as 10 MHz, etc.  I've even carefully measured each step to ensure there's no different factors involved.  The DRO reads properly, I can slew the frequency that's displayed to the center and read it correctly off of the DRO, but 30 MHz looks like it is 12 MHz from center on 2 MHz - Full Scale when making measurements off of the graticule.   Likewise, 1 MHz all the way down is a factor of 100 off.  I've combed through the tech manual and have found no troubleshooting sections that detail how to deal with this type of issue.  Although I can live with the fact that the display is 2/5 what it should be, the fact that my low end of the spectrum is mirrored to the top end is a real pain that I'd like to fix... however, I can't help but to think that these two issues are linked.   I'm running this in an HP 853A mainframe.

Thank you

Rob Stoddard  

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