BM869S not reading correct voltage

[J-R]

The BM869s is actually pretty well sealed.  There are gaskets/o-rings around the battery cover and the banana jacks, even the screw heads.  So I don't think humidity would impact it.

But you could still fully inspect the PCB under a microscope looking for any solder issues or corrosion, clean selector switch and jack contacts.

A side note is that each jack's BeepJack feature does not function if their respective fuse is blown, so double-check those.

What 9V batteries are you using?

[BeBuLamar]

Can you send it to manufacturer for repair at reasonable cost?