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@ElectronicsAndBooks.com Netherlands Discere ne cesses

Frans, 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. Todd On Wednesday, May 20, 2015, Electronics and Books via volt-nuts < volt-nuts@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@ElectronicsAndBooks.com > Netherlands > > Discere ne cesses > _______________________________________________ > volt-nuts mailing list -- volt-nuts@febo.com <javascript:;> > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there. >

I just read your post again and missed that you reflowed the solder joints. I will have to stop reading posts with my phone. Todd On Wed, May 20, 2015 at 3:52 PM, Todd Micallef <tmicallef@gmail.com> wrote: > Frans, > > 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. > > Todd > > > On Wednesday, May 20, 2015, Electronics and Books via volt-nuts < > volt-nuts@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@ElectronicsAndBooks.com >> Netherlands >> >> Discere ne cesses >> _______________________________________________ >> volt-nuts mailing list -- volt-nuts@febo.com >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts >> and follow the instructions there. >> >