Repaired Harbor Freight digital caliper

[P E Schoen]

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

 

[N_Cook]

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

 

[William Sommerwerck]

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.

 

[amdx]

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

 

[N_Cook]

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

 

[Stormin Mormon]

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
..


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

 

[N_Cook]

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

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?

 

[N_Cook]

work.


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

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"

 

[Fred Abse]

That's why I like the Dial calipers vs Digital Calipers, no concern
about batteries or electronics.

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 ;-(

 

[Jamie]

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"

I have the HF digital calipers and I need to pull the battery when not
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

 

[Jamie]

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?

And the engineer was correct in saying so.

Jamie

 

[Bob Engelhardt]

I have the HF digital calipers and I need to pull the battery when not
in use other wise, it'll be dead next time I need it. It seems to drain
quite fast.

....

I have one & the battery lasts quite a while (doesn't get used much).
Maybe a different model. Or a different batch. Or different spots on
the quality curve <G>.

Bob

 

[Martin Riddle]

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 have a vernier Calipe. I never need to set the dial, cause there isn't
one

Cheers

 

[mike]

As do I.

My Mitytoyo digital mics..never could figure out how they work
though..Ive got one thats had the same battery in it for 4 yrs so
far..still reading just fine and its always displaying whenever I open
the box

Gunner

Same here.
I bought several of the Harbor Freight ones back when they were on sale.
They're always dead. I have to take the battery out when not in use.
PITA, but I'm gonna have to replace it anyway if I leave it in.

My Mitutoyo has been going strong for years on the same battery.

 

[P E Schoen]

"Stormin Mormon" wrote in message

Cleaned, how? Trichlor? WD? Cotton swab?

I used rubbing alcohol, which I also use for defluxing PCBs. I also scraped
the surface and dried it with a paper towel.

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

I've lived with the problem for a long time. I have two houses, adjacent to
each other, and the lower levels have a stone foundations built into a hill.
It is worse in the house where I have my workshop and storage. And the
houses are in a low-lying area under lots of trees and the water table is
close to the surface. I've also had leaks in the foundation as well as the
roof so moisture has gotten in. Some time ago I basically gutted both houses
and replaced the old rotten frame studs and mud sills with new
pressure-treated lumber, but did not add vapor barrier, insulation, or new
drywall, until recently, and only partially. Being below grade, it's like
being in a cave, and it's often so cold that a dehumidifier freezes up. And
without insulation and vapor barrier, it's almost futile to try.

You can see my houses, and some of the work I've done (and some of my
tools), on youtube:

(there are also part 2 and part 3)

Paul
www.muttleydog.com

 

[Spehro Pefhany]

My cheap electronic caliper goes nuts when I transmit on UHF anywhere
near it. However, it doesn't require the battery removal ordeal to
recover. I just reset to zero and continue.


I beg to differ. The general package name is LR44 in an 11.6mm dia x
5.4mm thick package alkaline cell. There are slight variations, but
the IEC LR1154 equivalents (LR44/LR154, A76, 157/303/357) are all the
same size. Where you can have problems is that the SR44/SR1154 silver
oxide cells come in the same package. They have about 50% more
capacity and a much flatter discharge curve. Some of the cheapo
calipers crap out below about 1.4V. The alkaline battery has plenty
of capacity left at 1.4V, but the caliper doesn't want to run. If
your caliper cames with a silver-oxide cell, it should probably use
silver oxide batteries. If it came with alkaline and has a short
battery life, it might be worthwhile trying silver-oxide. If you're
ambitious, it might be useful to run the caliper off a bench power
supply and check how low a voltage will work.

Be sure to check how high a voltage too, and report back. ;-)



Best regards,
Spehro Pefhany

 

[Martin Riddle]

I just measured a Harbor Freight (Chinese) 8-incher.

Drain: 13.5uA (off), 14.5uA (on)
Battery low threshold (blinking display): 1.37V
Lowest operating voltage: 1.01V

So, it's clearly made for silver-oxide cells. The battery low
threshold is set appropriately for a silver oxide cell (e.g. SR-44).

It's a lousy threshold for using alkalines--they're barely broken in
at that voltage.

14.5uA means a year from a silver oxide cell--that's not horrible.

Why bother including an on off switch?

Cheers

 

[DoN. Nichols]

That's why I like the Dial calipers vs Digital Calipers, no concern
about batteries or electronics.

But -- dial calipers are vulnerable to two problems.

1) Drop or bump them and the pinion will disengage from the
rack and shift to give a wrong reading. You can work around
that by rotating the dial to re-zero it, but past a certain
point, it gets to be awkward to read.

2) Small chips can get engaged in the rack and the zero point
will shift every time you pass that point.

Vernier calipers don't have these problems, but are more
difficult to read with aging eyes and poor light.

Yes -- there are ways to fix both, but a lot more fiddly than
fixing an exhausted battery on the digital calipers.

And the digital calipers have two other advantages over dial and
Vernier calipers:

a) Switch between metric and inch modes at the push of a button,
even converting readings already locked in. (Actually, some
Vernier calipers have both scales, so this does not apply.)

b) Ability to reset the zero where-ever you want, so you can set
it to zero on a target dimension, and then read how much you
need to machine off in a lathe to see how many passes before
you are close enough to do serious measurements. You can even
keep a calculator handy to divide by two depending on whether
your cross-feed dial reads in diameter or radius.

c) (O.K. Three for some people. -- the ability to transfer the
measurement to a computer (without typing errors) for statistics
or other similar processing.

(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.

I have three 6" (150 mm) digital calipers, and a 12" (300 mm)
digital caliper. (Not counting two old B&S 6" ones which require
mercury cells for power, which are made of unobtanium.)

I also have a two dial calipers -- a 6" Phase-II, and a 150 mm
Starrett.

And two Vernier calipers -- a 6"/150mm and a 24" (I forget
whether that one has metric units as well.)

However -- the ones which I reach for most of the time are the
digital ones -- because of the memory feature and the ability to switch
measurement systems to match what I am working on and with.

One 6" digital stays near the main lathe (12x24" Clausing) and
one near the little CNC lathe in the opposite corner of the shop. The
cheapest digital ($18.00 at a hamfest) lives up here by the computer for
when I want to measure something quickly.

I keep a spare cell (or set as appropriate) in the case of each
digital, so I am not out of operation for very long if the cells in the
caliper go bad.

The dial or the Vernier get used when I expect to be away from
batteries for a while -- or in case the production of batteries ceases
thanks to some apocalypse. (Or the 24" one for when I need to
measure beyond the range of the 12" digital.)

Enjoy,
DoN.

 

[DoN. Nichols]

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

Most of the newer ones dont really switch off -- just the
display is blanked to save power, so the reading is preserved. (But,
the battery life is not as good. On the Starrett ones which I have, the
battery holder slides in and out, and by sliding it less than 1/16" you
can disconnect the battery (thus extending the life) at the cost of
having to re-zero when you power them back on. I normally do exactly
this.

The Mitutoyo is not as convenient to disconnect the batteries,
so I live with it -- but it also has an extra feature. Aside from
remembering when turned off -- it can remember two zeros -- the absolute
zero, and the incremental zero (say you zero it to tell how much left to
remove in the lathe), and by pushing a button, you go back to the
absolute zero without having to clean the jaws and check.

Enjoy,
DoN.

 

[DoN. Nichols]

[ ... ]

I have the HF digital calipers and I need to pull the battery when not
in use other wise, it'll be dead next time I need it. It seems to drain
quite fast.

How fast it dies is in part a function of the quality of the
batteries used. There are two series, "44" and "357" which are
interchangeable (and both magnum handgun calipers, FWIW) which can be
either Alkaline cells, or Silver Oxide cells. The Silver Oxide (usually
a "SR" prefix to the number) gives *much* better life -- at a
significantly higher cost. However, those more expensive ones are the
ones which I tend to use. The same in the digital micrometers, which
read down to 0.00005" or 0.001 mm.

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

They are nice to have -- and typically the more expensive ones
*do* work better.

Enjoy,
DoN.