1. Datron 1281 offset null, Bias current adjustments
    (starbook@uplink.net)
 2. Datron 1281 offset null, Bias current adjustments
    (starbook@uplink.net)
 3. Re: Datron 1281 offset null, Bias current adjustments
    (Electronics and Books)

The offset adjustment R317, is an AC adjustment, not DC as one might surmise. As I recall I applied a 10X scope probe to the O/P point at the junction of R329 and R330 to view the AC component. I probably used a 10Meg ohm with a cap in parallel, in a well shielded enclosure across the input jacks. I probably set the 1281 to the 10V range. As for R222 the input bias, I think I just barely touched up the adjustment so that there was little drift with the input open. That is, the input would float around a low displayed value, and climb to a large number in either polarity. I paraphrased the adjustment info from the 1081 and applied it as much as possible to the 1281. Another thing I learned from owning two, and working on a few more 1281's is that the first thing to do is replace all the aluminum electrolytic caps on the analog board as a minimum. Especially the small 1uf caps on the 3-terminal regulators die and the noise increases. This will cause all kinds of problems. I change them all, on all the boards. Due to the low profile of the larger caps careful selection is necessary. A few years ago I had email contact with one of the technicians at Fluke Farnborough, the home of the 1281. He wasn't much help, but indicated that internal adjustment procedures were never released. He wouldn't provide any details either.. Sorry for the nebulous response, but it has been awhile since I adjusted mine. Bob Koller On 5/23/2015 9:00 AM, volt-nuts-request@febo.com wrote: > Send volt-nuts mailing list submissions to > volt-nuts@febo.com > > To subscribe or unsubscribe via the World Wide Web, visit > https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > or, via email, send a message with subject or body 'help' to > volt-nuts-request@febo.com > > You can reach the person managing the list at > volt-nuts-owner@febo.com > > When replying, please edit your Subject line so it is more specific > than "Re: Contents of volt-nuts digest..." > > > Today's Topics: > > 1. Datron 1281 offset null, Bias current adjustments > (starbook@uplink.net) > 2. Datron 1281 offset null, Bias current adjustments > (starbook@uplink.net) > 3. Re: Datron 1281 offset null, Bias current adjustments > (Electronics and Books) > > > ---------------------------------------------------------------------- > > Message: 1 > Date: Sat, 23 May 2015 04:38:48 -0400 > From: <starbook@uplink.net> > To: Discussion of precise voltage measurement <volt-nuts@febo.com> > Subject: [volt-nuts] Datron 1281 offset null, Bias current adjustments > Message-ID: <55603C98.10501@uplink.net> > Content-Type: text/plain; charset=utf-8; format=flowed > > > I have a Datron 1281 DMM. > How to set the bias current adjustment (R222)? > How to set the offset null adjustment (R317)? > Thanks, > John Staron > > > ------------------------------ > > Message: 2 > Date: Sat, 23 May 2015 04:39:52 -0400 > From: <starbook@uplink.net> > To: Discussion of precise voltage measurement <volt-nuts@febo.com> > Subject: [volt-nuts] Datron 1281 offset null, Bias current adjustments > Message-ID: <55603CD8.9070009@uplink.net> > Content-Type: text/plain; charset=utf-8; format=flowed > > > I have a Datron 1281 DMM. > How to set the bias current adjustment (R222)? > How to set the offset null adjustment (R317)? > Thanks, > John Staron > > > ------------------------------ > > Message: 3 > Date: Sat, 23 May 2015 10:41:09 +0000 (UTC) > From: Electronics and Books <electronicsandbooks@yahoo.com> > To: Discussion of precise voltage measurement <volt-nuts@febo.com> > Subject: Re: [volt-nuts] Datron 1281 offset null, Bias current > adjustments > Message-ID: > <1942394052.99115.1432377669452.JavaMail.yahoo@mail.yahoo.com> > Content-Type: text/plain; charset=UTF-8 > > offset > looking at the schematics on page 11.2-3 the bias should be adjusted by shorting the inputs of the amplifier and then a zero output. > biasshorting the external input and measure the output of the amplifier > i could not find the internal adjustments in the manual. > Met vriendelijke groeten > Regards > > Frans > > > http://ElectronicsAndBooks.com > Netherlands > > Discere ne cesses > From: "starbook@uplink.net" <starbook@uplink.net> > To: Discussion of precise voltage measurement <volt-nuts@febo.com> > Sent: Saturday, May 23, 2015 10:39 AM > Subject: [volt-nuts] Datron 1281 offset null, Bias current adjustments > > > I have a Datron 1281 DMM. > How to set the bias current adjustment (R222)? > How to set the offset null adjustment (R317)? > Thanks, > John Staron > _______________________________________________ > 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. > > > > > ------------------------------ > > Subject: Digest Footer > > _______________________________________________ > volt-nuts mailing list > volt-nuts@febo.com > https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > > ------------------------------ > > End of volt-nuts Digest, Vol 69, Issue 19 > ***************************************** >