HP/Agilent/Keysight 34401A  2W Ohm strange phenomenon - Page 1
Forum section: electronics / repair

author: coldframe
author_rank: Regular Contributor
timestamp: September 20, 2014, 09:43:14 am
content: Hello Forum.34401A 2W Ohm strange phenomenonI already fixed previouslyhttps://www.eevblog.com/forum/testgear/34401a-cal-error-707/Thanks again Dr. Frank, free_electron, robrenzNew problems seem to come thick and fastI would like to do Fix this problem before Calibration RequestSymtoms0. Self Test Pass.1. Power on, 2W Mode button Press, OVLD OHM is Normal Display (Attached Photo : pic2)2. Touch my finger Hi Input Jack, "1xx M OHM" Dislay (Attached Photo : pic3)or, Power on, after a 2~3 minute lapse "1xx M OHM" Dislay (Attached Photo : pic4) * bottom unit3. Known good meter (Attached Photo : pic5)* upper unitAdd:4. Ohm OFFSET Error 722 (Cal 2-wire ohms function offset out of range)- Short front Input Jack then CAL-> CALIBRATE -> OHM 2,3,4 Beep* I am speculating phenomenon as the reason.* Other function normalIn my experience, Agilent/Keysight do not repair, only Change Mainboardunderstand that, but It's too expensive, too harshHow can I understand This situation?.Please share knowledgeThank You!~Reference. (an excellent article)https://www.eevblog.com/forum/testgear/34401a-cal-error-707/https://www.eevblog.com/forum/repair/hp-34401a-drift-in-the-2w-r-mode-in-the-100-ohm-range/Thank you Z, for sharing your knowledge

author: coldframe
author_rank: Regular Contributor
timestamp: September 26, 2014, 12:32:06 pm
content: My Unit Serial is 3145Axxxx Rev BI found great post,https://www.eevblog.com/forum/repair/hp-34401a-error-612-613-615-617-618-619-621/I Checked but looking a bit strange U201-B Pin 6,7 VoltageBlue : Zucca, Green : Dr. Frank, Red : MineHow can I understand This Situation?I would really appreciate any help.

author: coldframe
author_rank: Regular Contributor
timestamp: September 28, 2014, 06:54:53 am
content: Here below the some measure (Measured with a Fluke 189)Patient Meter,The DC current during 2W Ohm measurement0.63 uA in 100 M range0.63 uA in 10 M range5.11uA in 1 M range10.07 uA in 100 k range100 uA in 10 k range0.998 mA in 1 k range0.998 mA in 100 Ohm rangeThanks Again, HighvoltageThe DC Voltage during 2W Ohm measurement2.6154V in 100 M range4.7315V in 10 M range (unstable, increase slowly)6.202 in 1 M range6.676V in 100 k range7.726V in 10 k range7.244V in 1 k range7.244V in 100 Ohm rangeknown good meterThe DC current during 2W Ohm measurement0.59 uA in 100 M range0.59 uA in 10 M range5.15uA in 1 M range10.24 uA in 100 k range101.1 uA in 10 k range1.008 mA in 1 k range1.009 mA in 100 Ohm rangeThanks Again, HighvoltageThe DC Voltage during 2W Ohm measurement2.6533 in 100 M range5.078V in 10 M range7.318V in 1 M range7.312V in 100 k range7.230V in 10 k range6.808V in 1 k range6.808V in 100 Ohm range

author: Rick
author_rank: Frequent Contributor
timestamp: September 29, 2014, 06:56:58 pm
content: Quote from: coldframe on September 20, 2014, 09:43:14 amI have the same problem on one of my HP 3457a's.But the change is immediate. When I blow in the jacks I have the same effect. This affects the measurements.

author: SArepairman
author_rank: Frequent Contributor
timestamp: September 30, 2014, 08:50:32 pm
content: blowing on high impedance things seems to cause noise, are you sure one of the meter is not set to <10Gohm? play with an electrometer some time, it is fascinating, rubbing your hair 10 feet away causes readings.but my 34401a is not sensitive to this

author: coldframe
author_rank: Regular Contributor
timestamp: October 01, 2014, 08:04:14 am
content: hello Rick,SArepairmanYes the multimeter’s input resistance is 10M Ohm(default)I’ve read the Service manual, Artcle, but I’m still none the wiser.Display OVR.D OHM, When I touch my finger in the vicinity of Q203 (Attatched Photo, Green Cricle)Is is definitely not normal.Well, I have a day jobwhen not crowded with work, They are both currently being investigatedAnyway, I appreciate your interest.Regards.

author: Rick
author_rank: Frequent Contributor
timestamp: October 01, 2014, 10:31:11 pm
content: Quote from: coldframe on October 01, 2014, 08:04:14 amI did not mean to hijack your thread, sorry.Just to clarify:@SArepairman: the same behaviour is observed when nothing is connected to the inputs and I do not blow, but I simply touch the jacks or I do not, with 10 Gohm input impedance (I think it is 10Gohm).

author: motocoder
author_rank: Unknown
timestamp: October 02, 2014, 02:12:03 am
content: I just tried setting mine to 10G input resistance, but it does not exhibit this behavior.

author: Zucca
author_rank: Unknown
timestamp: December 20, 2014, 01:38:36 pm
content: Quote from: coldframe on October 01, 2014, 08:04:14 amJust jumping on this without thinking too much, sorry if I overlooked something....Did you had a short between + and - post so the display was 0R and then OVR?Is the problem reproducible when you tap the same spot with an isolated object like a plastic pen? If yes try to reflow the components there.