After the repair, i've noticed ( by playing with meter's function) that by pressing auto-test button, auto-cal test #5 and #4 are failing, but where it get interesting is that after 10 minutes of operation #5 failure has disappears and 5 minutes later #4 failure goes off too, that's very strange, it's like the meters is warming up...
I've gone through the manual but so far i've not tested anything but i've looked at the components that are maybe faulty and look for an economic way to replace them... not a easy job, since every component like MC1436CG or HA2-2526 are not produced anymore and they cost more than 50 euros each...that's not worth it for an 15 euros meters...
Anyway, i just want a feedback on what that could cause a such weird behavior.