[volt-nuts] 3458A resistance calibration

Todd Micallef tmicallef at gmail.com
Wed May 20 15:52:37 EDT 2015


I had two 3458a fail that resistance cal. I eventually replaced the front /
rear switch. The easy way to test it is to measure the resistance with the
front panel jumpered and then short the internal  black and white cables at
the A1 board and measure the difference. I also had one with a bad cable in
addition to the switch. The cables develop small breaks just behind the
crimps. Wiggling the cable showed how bad it was. Both were available for
order the last time I needed them.


On Wednesday, May 20, 2015, Electronics and Books via volt-nuts <
volt-nuts at febo.com> wrote:

> my 3458 was getting troubles with the calibration of the zero. As volts
> where no problem and ohm were pretty accurate, my conclusion was that there
> is basicly nothing wrong. the calibration stopped at the ohm-10. so it must
> be in the sense lines somewhere. on de dc print there where 2 big resistors
> (Dale ?) in the sense lines. with a magnifying glass i could spot litle
> cracks in the solder. after heating with some fresh solder the fault was
> over.
> i have red several times that the standard resistor for ohms should be of
> a better type. In my 1998 production unit it is a vishay vhp101 40k. that
> must be one of the better ones that were made by vishay. in an older 1994
> unit there was no brand or recognisable type code on it.
> Regards
> Frans
> info at ElectronicsAndBooks.com
> Netherlands
> Discere ne cesses
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