Fluke 12 Multimeter Display Problem
jaugu...@verizon.net
Back in 1995, I bought a Fluke "12" Multimeter (digital) because of a
special feature (Max & Mim) it has. I have not used that meter often over the
years, unless I needed to use that special feature.
I have a display problem. Not all the segments of a digit are "active".
I had worked on this problem more than once over the years. The display
panel has those problematic edge contacts.
Does anyone know of a good fix for this problem?
Thank You in advance, John
PS, Remove "ine" from my email address
N_Cook
news:rpmmd5p3kpe6c11oo...@4ax.com...
If zebra contacts, clean all surfaces with a very light solvent and turn
around before replacing, if not enough then create less spacing, ie squash
the strips slightly more by changing the board/LCD anchoring/posistioning
structures .
--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/
jaugu...@verizon.net
That is what I have done, but I use a special cleaning 100% alcohol I
ordered from MCM Electronics years ago.
John
On Mon, 19 Oct 2009 11:16:41 -0400, in sci.electronics.repair you wrote:
>On Sun, 18 Oct 2009 14:17:59 -0400, jaugu...@verizon.netwrote:
>
>>Hi,
>>
>> Back in 1995, I bought a Fluke "12" Multimeter (digital) because of a
>>special feature (Max & Mim) it has. I have not used that meter often over the
>>years, unless I needed to use that special feature.
>>
>> I have a display problem. Not all the segments of a digit are "active".
>>I had worked on this problem more than once over the years. The display
>>panel has those problematic edge contacts.
>>
>> Does anyone know of a good fix for this problem?
>>
>> Thank You in advance, John
>>
>>PS, Remove "ine" from my email address
>
>If you remove and clean the edges of the display and all the contact
>points and its connections to the board with 90% alcohol with a
>lintless swab that should restore the display for another few years if
>not longer. I've done this to my Fluke 77 twice in the 20 years I've
>had it.
jaugu...@verizon.net
Yes, that procedure works for a while (a year or so), but eventually, it
has to be done again.
John
On Thu, 22 Oct 2009 09:59:57 -0400, in sci.electronics.repair you wrote:
>On Wed, 21 Oct 2009 07:37:34 -0400, jaugu...@verizon.netwrote:
>
>>Hi Meat Plow,
>>
>> That is what I have done, but I use a special cleaning 100% alcohol I
>>ordered from MCM Electronics years ago.
>>
>> John
>
>Well I assume it worked out ok for you. We used to use a 100% alcohol
>for swabbing tape heads back in my days as a warranty service tech for
>Circuit City's mobile audio stuff.
N_Cook
news:fb53e5logc4rnq4fr...@4ax.com...
The rubber permanently relaxes so you have to narrow the spacing/ increase
the closure force, ISTR running a film of solder over the pcb lands in one
such case, otherwise change/cut back any spacing arrangement, ie not
increased pressure on the glass
Jeff Liebermann
wrote:
>> >>>If you remove and clean the edges of the display and all the contact
>> >>>points and its connections to the board with 90% alcohol with a
>> >>>lintless swab that should restore the display for another few years if
>> >>>not longer. I've done this to my Fluke 77 twice in the 20 years I've
>> >>>had it.
I have a Fluke 10 and a Fluke 77. Over the last 10 and 20 years
respectively, I've had to clean each roughly every 5 years. I used
ordinary 90% alcohol and let it air dry before reinstalling. 100%
alcohol is hydroscopic and rapidly absorbs moisture from the air.
Alcohol also tends to harden rubber, which is not a great idea for a
rubber connector.
What seems to work the best is xylene based "rubber restorer" that I
use for softening the rubber rollers in laser printers.
<http://www.fixyourownprinter.com/specials/misc/all/S03>
It did some experimenting and found that it causes the rubber to
soften and swell slightly, which was exactly what I needed.
However, there was a problem. LCD's don't draw much current so Fluke
used the cheaper carbon conductive Zebra connector instead of the more
expensive silver contacts.
<http://www.fujipoly.com/products/genProductLine.asp?ProductLine=Zebra>
<http://www.fujipoly.com/design/genDesignGuidelineArticle.asp?ContentItemID=dga_1010>
<http://www.fujipoly.com/PDF/2007_Catalog.pdf> (4.5MB)
The strip tends to deform and stay deformed if compressed. Note that
the Zebra connector is intended to be compressed 8% to 20% with 10% to
15% as the target value. You can see it with a microscope.
I learned all this the hard way dealing with display failures in a
product I helped design. Products would get returned for various
other failures. However, when reassembled, the LCD display would show
missing segments.
I built a fixture (milled slot in an aluminum block with a flat cover.
Drop the old Zebra connector inside, slop some rubber restorer on the
strip, and slightly compress from the ends. This worked, but was
strictly an experiment, and not intended to be a repair procedure.
What we found was that over compressing the Zebra connector would
create an uneven edge, which would not make very good contact. Someone
noticed that the worst connection problems were in the middle of the
Zebra strip. That's where the customer and techs, trying to repair
the problem would squeeze the PCB and LCD together, bending the PCB
slightly. That would temporarily increase the connector pressure, but
result in a bad connection when released. Resist the temptation to
squeeze the strip. We reduced the compression to about 10% which
eliminated the visible deformation. Reassembling the Zebra strip in
the original orientation was also a big help.
Someone later discovered that the PCB was bending slightly in wave
soldering. Stiffeners were added prior to soldering, which totally
eliminated the problem.
>The rubber permanently relaxes so you have to narrow the spacing/ increase
>the closure force, ISTR running a film of solder over the pcb lands in one
>such case, otherwise change/cut back any spacing arrangement, ie not
>increased pressure on the glass
I'm fairly sure that won't work. The problem is that there's no way
to insure that the soldering is the same height across the strip. Some
solder lumps will be higher than others, resulting in an uneven
compression of the rubber. If you then move the Zebra strip even
slightly, you'll end up with air gaps in the over-compressed areas.
Incidentally, Zebra connectors are also a problem with HP41C series
calculator.
More:
<http://www.repairfaq.org/REPAIR/F_audiofaqc.html#AUDIOFAQC_012>
--
Jeff Liebermann je...@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
Bob Larter
If you do that, don't forget to remove any flux from the built-up pads
with alcohol.
--
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\|/ \|/ it is illegal to kill them." Perna condita delenda est
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