HP 3468A Tragedy! Changed Lithium Battery but Cal parms hosed! (Error 1) - Page 1
Forum section: electronics / testgear

author: k6whp
author_rank: Newbie
timestamp: September 28, 2015, 12:46:04 am
content: Caveat: been through most of the threads here and have only found the caveat/procedures for replacing the backup battery.Despite taking proper precautions, my efforts at replacing the Lithium backup cell failed and I glitched my unit's parms. I do not mind paying for a reasonable calibration service -- $50-75 -- but I cannot seem to find anything under $125 ~~ and that's a little steep for a hobby bench unit.That said, I have been reviewing section 4 of the HP service manual and have tried out a little bit of the Cal procedure without success. Here is what I am wondering:(1) It is necessary to have standards or an accurate DMM (i.e., calibrated HP 3478A, etc.) measuring a stable DC supply at the 300 mV, 3 V, 30 V levels, etc., correct.(2) There's no way one could press a voltage standard into service to measure at the standard's levels (i.e., 0.5V, 1.0V 2.5V, etc.)(3) Similarly, I have calibrated resistances of 100, 1000, 10,000, and 100,000 ohms. Can I do a calibration them.But I guess the biggest take-away is has anyone ever personally done the calibration procedure and can i bounce some questions off you as to how it is done.Thanks for any help!~Bill, k6whp

author: singapol
author_rank: Frequent Contributor
timestamp: September 28, 2015, 03:34:35 am
content: EEVblog is not the only source of info...here is a battery replacement tuitorial:http://mrmodemhead.com/blog/hp-3468a-battery-replacement/Since you botched it up you can still calibrate it yourself of course it's dependent on howprecise/accurate your voltage refs and resistors are. You can get a 3V voltage reference and connect in series 3 X 10V references to get 30V.For 300mV. You can use/construct a Kelvin Varley voltage divider to get a 300mV reference subject to tolerances. Search eevblog.

author: cncjerry
author_rank: Unknown
timestamp: September 28, 2015, 04:49:06 am
content: if you have standards you can calibrate it yourself. The first step is to download the manual. You calibrate each range high and zero. In both cases you can used the arrow buttons to bring the calibration value displayed to the known value of your standard. It is easiest to use GPIB to set the values otherwise you have to hold the arrow buttons as it steps to the value you need. The 3478 uses the 3xxx values but you can also use the 1xxx values but I can't remember if you have to step to the 1xxx value or if it will be preloaded into the display as in the 3xxx ranges. I use GPBIB to load the calibration standard values and it makes it a lot easier.I've calibrated 3 or 4 of them to my standards. It's pretty easy to do and I often reset the zero on certain ranges depending on the leads I'm using. The hardest standard to hit is the 300v range but you can use 100v with lesser accuracy. You have to calibrate each range before the calibration error will go out.

author: ModemHead
author_rank: Frequent Contributor
timestamp: September 28, 2015, 03:37:55 pm
content: Welcome to the forum K6WHP (small world, eh?) Sorry to hear of your "tragedy". Do you know what could have caused the glitch? I can update my procedure with extra cautions if necessary, to help others avoid the problem.

author: Stray Electron
author_rank: Super Contributor
timestamp: September 28, 2015, 04:52:48 pm
content: You might want to take a look at the 'HP Journal' article about the 3468A. It explains a lot about the calibration including the fact that you can do each range calibration individually and that you can use 0 to 3 *10^x sources or 0 to 1 *10^x sources. <http://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1983-02.pdf>. Do you have another calibrated meter that you can calibrate it against?