I have an EEVBlog Brymen BM786 about 2 years old that has a problem. The burden resistance when measuring mA and uA is highly variable, especially with even slight movement of the meter. For instance, the manual implies 2.0 Ohms for the mA range and other users have reported 2.4 Ohms. Sometimes I can get results in that ballpark, but other times it shoots up to 9-10 Ohms or more, especially if the meter is tapped lightly. The resistance typically settles back to some new reading. By including another meter in series, I can confirm that the current readings vary as expected with the changing burden voltage.
I’ve tried reversing the roles with other meters (121gw and a Fluke) to check that this behaviour is only a property of this BM786. I suspected dirty fuse contacts, but I cleaned those with no improvement. Ditto for cleaning the input jacks and using different cables. I also thought of cracked traces or solder joints, but I can’t see anything (although I don’t have much experience, so I may have missed something).
Any ideas? What to look for?
Should I distrust the meter? Only on current measurement or on everything?
Thanks for any help.