GDM-8251A

[GigaJoe]

in overall i like it but it always sitting aside, for some reason, and one of them was constant jabbering of 2 last digits ....

so i finally decided to open and look inside .... and here we are ....

the power supply actually OTC 5V switching PSU,  with minimal filtration,
then it feeding onboard switching converter that convert 5V to +16 and -16 ( i think ... )
then linear regulators
and all this going to analog part of DMM.

in overall not really possible to change much of design,   I simply add ceramic caps as much as i can to 5V PSU, and additional possibly 12-15 low ESR poly. caps as separated, simply glue it to metal case ;  it has a lot empty space nearby PSU.
an additional caps , a lot like 6-7 on each output of switching converter on board.   and additional caps before and after linear regulators.
finally i add on top of every tantalum cap an additional poly electrolyte on 100-200 mkf

and after that dmm became really quiet , jumping +-1 microvolts,  ( quiet on everything) ...
 
guess it may help ....

 

[bdunham7]

That's interesting--I had one as well and the noise was one of the 5 main reasons I hated the meter.  Its quite surprising that they shipped a meter like that with such an obvious issue. The solution should have been well within their grasp! 

[Kleinstein]

Some linear regulators are a bit picky about the ESR of the capacitors at the output. Especially some LDOs don't like to have too low loss capacitors at the output. A combination of a lossy capacitor (e.g. classic electrolytic) and low ESR capacitors can still be OK.

Having a noise problem due to insufficient supply filtering / ripple is indeed embarassing.