Fluke 12 Multimeter Display Problem

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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

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.

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.

Hi Meat Plow,

Yes, that procedure works for a while (a year or so), but eventually, it has to be done again.

John

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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

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

Wonder if the connectors can be replaced? I suppose if they were still available you would have done so?

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I wnder if you could wrap them with one layer of electrical tape to stiffen them up a bit?

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.

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.

(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

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.

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.

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If you do that, don't forget to remove any flux from the built-up pads with alcohol.