P E Schoen wrote in message
...
I have two Harbor Freight digital calipers, item #47257, and I've had
problems with one of them especially, where the display will go blank. It
seemed to work sometimes if I squeezed the enclosure, and I thought it was a
bad battery or bad connection. But a fresh battery didn't work.

So I took it apart, which meant peeling off a foil backing to expose four
small phillips head screws, which removed the electronics module, and then I
removed the PC board with four even smaller phillips screws. The LCD display
connects to the board with a flexible conductive strip, which relies on
pressure to maintain contact. I cleaned it and the mating contacts on the
PCB, reassembled it, and it now works fine!

My house is always very humid and I think that's what caused the problem.
It's hell on all my tools. Everything is rusty or mildewed.

It's quite interesting to see the mechanism that is used to make
measurements. There is an array of PCB traces that are aligned with an array
of stripes along the length of the caliper, and (I assume) these create
pulses that are counted as the head is moved. But it also needs to know
which way the head is being moved. Probably something like a quadrature
encoder as used for rotary position sensing. I'll have to look it up.

Paul


++++

It is usually a Moire fringe counting mechanism. The system like when you
move along a street and look through a set of railings to another set of
railings and you see a moving "interference" pattern. Set 2 fine grills over
one another at slight relative angle and these fringes become wide enough to
be reliably counted by a relatively large opto device, 10 or more times
wider than the spacing between the grating lines