[time-nuts] Answer found: HP53132A anomaly

[Taka Kamiya]

I hope this will be helpful to someone.  I recently had to take one to calibration and testing.

I have two HP53132A counters.  Recently I've noticed funny behavior when I tried to run self-diagnostic on Front End.  One counter always succeeds, but another one always fails.  The second counter succeeds if I use one particular cable.
I didn't get the result like this when I do "ALL" but if I do "Front End" individually, it happens.  There are differences between the two.  When you do ALL, there is no relay chattering, and it actually works without input connected to the reference out.  It's odd that same test behave differently.  It may be version of firmware dependent.

So my setup was, from 10MHz in rear to a tee, coax to front input 1, tee out to input 2.  This always failed on this unit.  But always succeeded another unit.

I never noticed this, but THIS unit has a rear input BNC.  (never used those)  The way it's configured, the input amp connects to front input, then branches off to the rear.  So if I'm using front connectors, this coax to the rear acts like a stub.  It causes this kind of fails.  When we connected the same except using REAR input, it works every time.  It is also very sensitive that it goes to input 1 first, then to input 2.  Backward connection also causes it to fail.

According to HP's service manual, it says when rear terminal is installed, performance of front terminal is not guaranteed.  

I also found out, last digit fluctuating in loop back test on this model is NORMAL.  53131A tends to stay very stable at 10.00.....
This is not mentioned in manual.



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(Mr.) Taka Kamiya
KB4EMF / ex JF2DKG