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34401A problems on 4w resistance readings

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masterx81:
Hi!
I have a 34401A multimeter with a problem on the 4w resistance reading. I find the resistance a bit unstable, it takes a lot to stabilize, and when i select the front terminals, also without anything connected, i get some random readings. I've tried to check the bottom side of the board for flux residue, but it's really clean. I've read that also the front/rear switch itself can cause problems.

Any suggestion on what check for first?

Thanks!

coppercone2:
push the switch a bunch of times and see if it does anything

masterx81:
Already tried, not seen any improvement.

bdunham7:
What resistances are you reading that are unstable and how are the connections made.  Can you set up a good 4-wire short?

masterx81:

--- Quote from: bdunham7 on September 21, 2023, 09:22:32 pm ---What resistances are you reading that are unstable and how are the connections made.  Can you set up a good 4-wire short?

--- End quote ---
For example, shorting the terminals it start at 40mohm, and slowly goes to almost 0 in near 5 minutes. This after proper unit warmup. If i open the short, and redo it immediately, it start back at 40. I not use the meter often, but last time i've used it few months ago was working fine.
I use true kelvin 4 wire clamps.
If i leave the back connection empty, and set the rear measurement, i see overload, as it should. With same conditions, selecting the front terminals i see random resistances from 100ohm up to 100's of kohms, i'm pretty sure that in the past it wasn't doing this. With 2w mode all seem working fine.

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