Repaired Harbor Freight digital caliper

Sun Nov 20, 2011 4:01 am   

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

Sun Nov 20, 2011 5:19 am   

"P E Schoen" <paul_at_pstech-inc.com> wrote in
news:a4_xq.6861$ov2.2972_at_newsfe10.iad:


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

Sun Nov 20, 2011 6:18 am   

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


<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_at_cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Sun Nov 20, 2011 9:41 am   

P E Schoen <paul_at_pstech-inc.com> wrote in message
news:a4_xq.6861$ov2.2972_at_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

Sun Nov 20, 2011 11:38 am   

"Jim Yanik" <jyanik_at_abuse.gov> wrote in message
news:Xns9FA2ED4AFED51jyaniklocalnetcom_at_216.168.3.44...


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.

Sun Nov 20, 2011 1:41 pm   

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

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

Sun Nov 20, 2011 2:03 pm   

amdx <amdx_at_knologynotthis.net> wrote in message
news:4756b$4ec8f55d$18ec6dd7$12472_at_KNOLOGY.NET...



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

Sun Nov 20, 2011 2:17 pm   

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_at_pstech-inc.com> wrote in message
news:a4_xq.6861$ov2.2972_at_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

Sun Nov 20, 2011 2:29 pm   

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_at_mindspring.com
ANTI-SPAM: To email, replace "lastname" with "plumpe"
"N_Cook" <diverse_at_tcp.co.uk> wrote in message
news:jaatmo$4n4$1_at_dont-email.me...

Sun Nov 20, 2011 2:33 pm   

On Sun, 20 Nov 2011 06:41:03 -0600, amdx <amdx_at_knologynotthis.net>
wrote:


I bought one of those and really like it. It seems comparable to
calipers costing many time more. The only problem is I have to remove
the battery when I am done using it or it is dead the next time I get
it out. I have a feeling that is why they were selling them for
$9.99. Fortuneately, it is easy to remove and reinsert the battery.

Sun Nov 20, 2011 2:38 pm   

Dave Plumpe <lastname_at_mindspring.com> wrote in message
news:dcCdnbxH1tldnVTTnZ2dnUVZ_qednZ2d_at_earthlink.com...

An engineer told me never close the jaws of a micrometer or vernier calipers
for storage, leave the jaws open slightly. Do these digitally things require
the jaws closing before switching off ? How do they know of any movement of
the jaws when switched off elsewise?

Sun Nov 20, 2011 2:41 pm   

<stans4_at_prolynx.com> wrote in message
news:0156c7a7-8bb2-4f32-922b-89bdd893a682_at_u6g2000vbg.googlegroups.com...
On Nov 20, 6:03 am, "N_Cook" <dive...@tcp.co.uk> wrote:

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

+++

So that explains , down thread, the drawback of dying batteries when
switched "off"

Sun Nov 20, 2011 3:25 pm   

On Nov 20, 6:03 am, "N_Cook" <dive...@tcp.co.uk> wrote:

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

Sun Nov 20, 2011 5:19 pm   

On Sun, 20 Nov 2011 06:41:03 -0600, amdx wrote:


I prefer a "proper" vernier. At least you can verify those by eye.I never
did trust digital calipers to hold their zero and not skip under workshop
conditions, Half a lifetime dealing with incremental encoders has made me
wary.

I *might* trust a Mitutoyo digital caliper or height gage in inspection
room conditions.

Dial calipers have all sorts of racks and gears to go sloppy.

I suppose nobody under fifty knows how to read a real vernier, or a slide
rule for that matter ;-(

--
"For a successful technology, reality must take precedence
over public relations, for nature cannot be fooled."
(Richard Feynman)

Sun Nov 20, 2011 5:22 pm   

N_Cook wrote:


in use other wise, it'll be dead next time I need it. It seems to drain
quite fast.

Other than that, it seems to work very nicely..
Jamie