The LF356 has slew rate spec'd at +/- 15V supply, the specsheet shows normal operation not lower than +/- 15V. The scope shows slew rate here about 2.2V/2uSec so not quite up to par.
Quick fix: change R21 to 2.7k or 3.3k
Yeeeey! Finally! With the change of R21 to lower value I was able to adjust for FS and even tried a capacitor, it seems to be working!
Could you please explain what you meant with the slewrate quite not up to par?
For what I understood was that because I'm powering the opamp with +6V and -4.4V the IC isnt speced for this operation and thus might not be operating has on the datasheet.
I'll give the diagram a new study and try to understand why the slower slewrate of the fake TL082 caused all this trouble.
The fix you purposed was because I'm going to get a higher gain with lower value R21 and thus would get "quicker" to the required voltage for the differential amplifier right?
Nonetheless with all this trouble and IC not working in the specification they were meant to, I'll propably give it a try to the Jay-Diddy's variant.
Can't stress enough how thankfull I'm for all your effort and sticking with me until the end SuzyC! Thanks a bunch my friend!