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

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