HP/Agilent/Keysight 34401A 2W Ohm strange phenomenon

[coldframe]

Hello Forum.

34401A  2W Ohm strange phenomenon

I already fixed previously
https://www.eevblog.com/forum/testgear/34401a-cal-error-707/
Thanks again Dr. Frank, free_electron, robrenz

New problems seem to come thick and fast 
I would like to do Fix this problem before Calibration Request

Symtoms

0. 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 unit

3. Known good meter (Attached Photo : pic5)
   * upper unit

Add:
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 normal

In my experience,  Agilent/Keysight do not  repair, only Change Mainboard
understand that, but It's too expensive, too harsh
How can I understand This situation?.
Please share  knowledge
Thank 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

[coldframe]

My Unit  Serial is 3145Axxxx Rev B

I 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 Voltage
Blue : Zucca,  Green : Dr. Frank, Red : Mine
How can I understand This Situation?

I would really appreciate any help.

[coldframe]

Here below the  some measure (Measured with a Fluke 189)

Patient Meter,
The DC current during 2W Ohm measurement
0.63 uA in 100 M range
0.63 uA in 10 M range
5.11uA in 1 M range
10.07 uA in 100 k range
100 uA in 10 k range
0.998 mA in 1 k range
0.998 mA in 100 Ohm range
Thanks Again, Highvoltage

The DC Voltage during 2W Ohm measurement
2.6154V in 100 M range
4.7315V in 10 M range (unstable,  increase slowly)
6.202 in 1 M range
6.676V in 100 k range
7.726V  in 10 k range
7.244V in 1 k range
7.244V in 100 Ohm range


known  good meter
The DC current during 2W Ohm measurement
0.59 uA in 100 M range
0.59 uA in 10 M range
5.15uA in 1 M range
10.24 uA in 100 k range
101.1 uA in 10 k range
1.008 mA in 1 k range
1.009 mA in 100 Ohm range
Thanks Again, Highvoltage

The DC Voltage during 2W Ohm measurement
2.6533 in 100 M range
5.078V in 10 M range
7.318V in 1 M range
7.312V in 100 k range
7.230V in 10 k range
6.808V in 1 k range
6.808V in 100 Ohm range

[Rick]

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 unit

I 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.

[SArepairman]

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

[coldframe]

hello Rick,SArepairman

Yes 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 job
when not crowded with work, They are both currently being investigated

Anyway, I appreciate your interest. 

Regards.

[Rick]

hello Rick,SArepairman

Yes 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 job
when not crowded with work, They are both currently being investigated

Anyway, I appreciate your interest. 

Regards.

I 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).

[motocoder]

I just tried setting mine to 10G input resistance, but it does not exhibit this behavior.

[Zucca]

Display OVR.D  OHM, When I touch my finger in the vicinity of Q203  (Attatched Photo, Green Cricle)
Is is definitely not normal.

Just 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.