[volt-nuts] Fluke 720a self calibration repair

[David Garrido]

Hello All,

I am trying to track down what I think is a small issue in the calibration of my new to me 720a.  I am dreadfully paranoid of jacking something up in the process and need a little hand holding.

I was going through the Self Calibration steps and every thing was going well up to the adjustment of the "A 1.0" decade switch position.  All of the variable resistors up to that point needed to be turned CW in order to null the appropriate switch position.  The “A 1.0” adjustment pot does not null the switch position and is not getting any closer than about 2.5uV.  I verified the meter balance between every other step.  I have checked, in circuit, R302 and R303 and I am getting a VERY SOLID reading of 9.896 on all of those.  Of course, checking R1006 and R1010 give me significantly different readings than the stipulated 8.45k.

I cannot seem to be able to find a CCW or CW limit to this resistor and I think I read somewhere that there are supposed to be run from end to end several times if an issue arises.  Do these var resistors have limits?  I need a little help moving forward.

Cheers,

David