"P E Schoen" wrote in
:

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



use Boeing Boeshield T-9 to prevent the rusting of your tools.

I wonder if Cramolin/DeOxit would work on the conductive strip?

--
Jim Yanik
jyanik
at
localnet
dot com