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
Repaired Harbor Freight digital caliper
Started by ●November 19, 2011
Reply by ●November 20, 20112011-11-20
"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
Reply by ●November 20, 20112011-11-20
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
Reply by ●November 20, 20112011-11-20
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
Reply by ●November 20, 20112011-11-20
"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.
Reply by ●November 20, 20112011-11-20
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
Reply by ●November 20, 20112011-11-20
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 > $9.99, I bought two. They are still in the boxes and I use my Dial > calipers. I think I might give one away as a Christmas present. > MikekI've never used the new-fangled ones - do you have to do a clean jaws, close jaws, zero calibration check/0 reset ,every time you use them ? as the count must be lost each time it is switched off
Reply by ●November 20, 20112011-11-20
Cleaned, how? Trichlor? WD? Cotton swab? Have you considered something to reduce the humidity, like vent fan, central AC, or dehumidifier? -- Christopher A. Young Learn more about Jesus www.lds.org . "P E Schoen" <paul@pstech-inc.com> wrote in message news:a4_xq.6861$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
Reply by ●November 20, 20112011-11-20
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 offUsed 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
Reply by ●November 20, 20112011-11-20
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 >