This answer is way off in left field but: Does tightening down the single
screw effect ground?  Do you have your box common grounded or seperate
ground?  Is it a metal or plastic box?

"Peter L. Peres" wrote:

> Hi,
>
> I am completely stumped by this one, so I submit it to an entity with more
> experience. I have a simple analog measuring circuit that outputs a
> voltage between 1.5 and 2.5V vs. a reference of 1.5V. This goes to a DMM
> using ICL7106 and a LCD as a display (in differential mode). Everything
> works but when I close the box and screw it down the ICL readout increases
> by about 20mV. It increases linearily as I tighten the single screw.
>
> The analog voltage is checked and ok with a Fluke DVM. The ICL does this.
> I have never seen such a thing. I have checked that there are no
> components under tension (mechanical). All the modules are hot-glued to
> the front of the box for trials so there is no way some bracket presses
> the wrong way.
>
> The DMM is a module which I have hacked slightly. It is built on 1.8mm FR4
> with through holes, zebra mounted LCD with elastic plastic bracket and the
> ICL is socketed in a solid socket.
>
> The change also occurs if I press on the front of the box (no matter
> where). Nothing touches the parts from the backside (there is a 3/4"
> clearance to the bottom of the box).
>
> Any ideas are very welcome,
>
> thanks,
>
> Peter
>
> --
> http://www.piclist.com hint: To leave the PICList
> mailto:piclist-unsubscribe-request@mitvma.mit.edu

--
http://www.piclist.com hint: To leave the PICList
mailto:piclist-unsubscribe-request@mitvma.mit.edu