several Moteino R6 shows different results on analog pin A2 [it's flux residue!]

[d00m178]

Hi.
I have several R6 and use A2 pin in my circuit to read Vcc for voltage batt monitor.

One new R6 module shows strange result (1.05v on my Lipo) on the same circuit board where another R6 modules shows normal value - 4.05v

I've checked A1 - and the same - this one new R6 shows wrong result.

Bad MCU module? is it possible that analog pin works in this wrong way - it works but show wrong values. ?

[d00m178]

just checked another of my Moteinos and I have very strange results.
all MCU is R6, some of them ordered on different orders, some - in the same order. 3 of them - just new.
code/firmware - the same
battery - the same
PCB with voltage divider - the same.
I changing only Moteino. And I receive different results - from 4.05v which is most similar to value from my multimeter to 0.66v which is ridiculous.
two old MCU show good results - 4.05v and 3.90v but two brand new MCU - 0.75v and 0.66v
How it is possible that on different MCU the analog pin show different results??

[Felix]

I have several R6 and use A2 pin in my circuit to read Vcc for voltage batt monitor.

Maybe if you would detail your battery monitoring circuit and code we would have a better idea what's going on?

Bad MCU module? is it possible that analog pin works in this wrong way - it works but show wrong values. ?

I say no way 

[d00m178]

I say no way 

sure, my bad.
I never imagined that soldering flux could be the culprit.
for those 2 new MCU I used new flux for solder headers to PCB.
and this flux is kind of "active" flux.
so it covered pins and probably add some resistance to voltage divider which leads to wrong reading.
after cleaning MCU with alcohol - everything starts working ok!
sorry for panic)