Repaired Harbor Freight digital caliper

I have two Harbor Freight digital calipers, item #47257, and I've had=20
problems with one of them especially, where the display will go blank. =
It=20
seemed to work sometimes if I squeezed the enclosure, and I thought it =
was a=20
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=20
small phillips head screws, which removed the electronics module, and =
then I=20
removed the PC board with four even smaller phillips screws. The LCD =
display=20
connects to the board with a flexible conductive strip, which relies on=20
pressure to maintain contact. I cleaned it and the mating contacts on =
the=20
PCB, reassembled it, and it now works fine!

My house is always very humid and I think that's what caused the =
problem.=20
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=20
measurements. There is an array of PCB traces that are aligned with an =
array=20
of stripes along the length of the caliper, and (I assume) these create=20
pulses that are counted as the head is moved. But it also needs to know=20
which way the head is being moved. Probably something like a quadrature=20
encoder as used for rotary position sensing. I'll have to look it up.

Paul=20

"P E Schoen" <paul@pstech-inc.com> wrote in
news:a4_xq.6861$ov2.2972@newsfe10.iad: 

> 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

On Sat, 19 Nov 2011 22:19:11 -0600, Jim Yanik <jyanik@abuse.gov>
wrote:

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

<http://siber-sonic.com/electronics/caig.html>
Sorta.  The original Cramolin contained about 5% oleic acid, which is
great for removing surface oxidation, but is also mildly corrosive to
copper.  The current version is DeOxit from Caig Labs.  It comes in an
amazing variety of forms, and is allegedly non-corrosive.
<http://store.caig.com/s.nl/sc.2/.f>
The MSDS data shows the active ingredients as a "trade secret".  Oh
well.

-- 
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

P E Schoen <paul@pstech-inc.com> wrote in message
news:a4_xq.6861$ov2.2972@newsfe10.iad...
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

"Jim Yanik" <jyanik@abuse.gov> wrote in message
news:Xns9FA2ED4AFED51jyaniklocalnetcom@216.168.3.44...

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

I assume the strip is carbon-impregnated rubber (or some synthetic polymer).
Cramolin/DeOxit remove surface oxidation. I don't the latter as being
compatible with the former.

On 11/19/2011 9:01 PM, P E Schoen wrote:
> 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.
>

That's why I like the Dial calipers vs Digital Calipers, no concern 
about batteries or electronics.
(Dial Calipers, Item # 66541, Out of Stock)

Although a couple years ago HF had the 6" Digital calipers on sale for
$9.99, I bought two. They are still in the boxes and I use my Dial 
calipers. I think I might give one away as a Christmas present.
                                  Mikek

amdx <amdx@knologynotthis.net> wrote in message
news:4756b$4ec8f55d$18ec6dd7$12472@KNOLOGY.NET...
> On 11/19/2011 9:01 PM, P E Schoen wrote:
> > 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.
> >
>
> That's why I like the Dial calipers vs Digital Calipers, no concern
> about batteries or electronics.
> (Dial Calipers, Item # 66541, Out of Stock)
>
> Although a couple years ago HF had the 6" Digital calipers on sale for
> $9.99, I bought two. They are still in the boxes and I use my Dial
> calipers. I think I might give one away as a Christmas present.
>                                   Mikek



I've never used the new-fangled ones - do you have to do a clean jaws, close
jaws, zero calibration check/0 reset ,every time you use them ? as the count
must be lost each time it is switched off

Cleaned, how? Trichlor? WD? Cotton swab?

Have you considered something to reduce the humidity, like 
vent fan, central AC, or dehumidifier?

-- 
Christopher A. Young
Learn more about Jesus
  www.lds.org
.


"P E Schoen" <paul@pstech-inc.com> wrote in message 
news:a4_xq.6861$ov2.2972@newsfe10.iad...
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

On Nov 20, 6:03=A0am, "N_Cook" <dive...@tcp.co.uk> wrote:
> amdx <a...@knologynotthis.net> wrote in message
>
> news:4756b$4ec8f55d$18ec6dd7$12472@KNOLOGY.NET...
>
> > On 11/19/2011 9:01 PM, P E Schoen wrote:
> > > 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 though=
t
> > > it was a bad battery or bad connection. But a fresh battery didn't wo=
rk.
>
> > That's why I like the Dial calipers vs Digital Calipers, no concern
> > about batteries or electronics.
> > (Dial Calipers, Item # 66541, Out of Stock)
>
> > Although a couple years ago HF had the 6" Digital calipers on sale for
> > $9.99, I bought two. They are still in the boxes and I use my Dial
> > calipers. I think I might give one away as a Christmas present.
> > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 Mik=
ek
>
> I've never used the new-fangled ones - do you have to do a clean jaws, cl=
ose
> jaws, zero calibration check/0 reset ,every time you use them ? as the co=
unt
> must be lost each time it is switched off

Used to be, they've improved things.  On at least some, the count is
kept live and just the display is switched off.  It all goes away when
batteries are switched, but that can be lived with.

Stan

Not only do they remember where Zero is, they even keep track of any 
movement that occurs while they're turned off.  Smart little devils.

I find myself more & more reaching for the digital ones for the ease of 
swapping between inches & millimeters.

-Dave
-- 
http://plumpe.home.mindspring.com
email: lastname@mindspring.com
ANTI-SPAM: To email, replace "lastname" with "plumpe"
"N_Cook" <diverse@tcp.co.uk> wrote in message 
news:jaatmo$4n4$1@dont-email.me...
>
> I've never used the new-fangled ones - do you have to do a clean jaws, 
> close
> jaws, zero calibration check/0 reset ,every time you use them ? as the 
> count
> must be lost each time it is switched off
>