Repaired Harbor Freight digital caliper

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
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use Boeing Boeshield T-9 to prevent the rusting of your tools.
I wonder if Cramolin/DeOxit would work on the conductive strip?
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Jim Yanik
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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.
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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.
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On 11/19/2011 11:19 PM, Jim Yanik wrote:

Hello, and DeoxIT is the best thing I've ever come across for cleaning and de-oxidizing electrical contacts. It also does wonders with scratchy volume and tone pots and it'll be long while before you have to apply it again. Sincerely,
--
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amdx wrote:

http://www.harborfreight.com/preview-thanksgiving.html?utm_medium=email&utm_campaignG11a&utm_source03

Nice, I like the metal cutting saw they have there just off to the right..
Think I'll do a stop in for that.
Jamie
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On 11/21/2011 6:49 PM, Jamie wrote:

Do note, it is pneumatic. Fine if your setup for it. Mikek
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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
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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
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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
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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
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work.
close
count
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"
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N_Cook wrote:

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
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Jamie wrote:

...
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
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    [ ... ]

    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.

    They are nice to have -- and typically the more expensive ones *do* work better.
    Enjoy,         DoN.
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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
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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?
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N_Cook wrote:

And the engineer was correct in saying so.
Jamie
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wrote:

True. With gear type calipers, the lubricating grease tends to migrate to that position. If a sufficiently filthy environment, an lump of dirt encrusted grease will be left in that position. If it happens to be at 0.0, then it will be difficult to accurately calibrate the mechanism. There are also some minor reasons, such as the tendency for two parallel surfaces to trap moisture between them and rust.

No.
Only the display is turned off. The pulse counting mechanism is still operating and functional. The downside is that the battery will be dead in about 6-9 months. Most include a spare LR44 battery. I had to buy a pile of them to keep my calipers going. Somehow, the battery is usually dead when I need to use them.
50 batteries for $3.75 <http://www.ebay.com/itm/220751739681
I have an expensive set of Starett calipers (both metric and US). I use them more often than the electronic variety, mostly out of habit. My most useful measuring tools are my 6" pocket steel scale and a tape measure.
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Jeff Liebermann snipped-for-privacy@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
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