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'[EE] Connector technology ??'
2007\10\09@201427 by Carl Denk

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I have Sharp countertop microwave oven model R-428JKF That has problems
that seems more like an intermittent "start" switch. The switches  are
on one PCB, the electronics (cpu) are on another , and the display  on
what appears to be a glass or clear plastic plate. The PCB board has
card edge consisting of approximately 50 parallel maybe 20 gauge nickel
or silver plated wires , the wire diameter flat is on the board with a
pitch of .05" approximately. These wire contacts are against a flexible
plastic strip 2.1" long, 1/4" high (perpendicular to PCB and length of
wires), and 0.115" thick (parallel to PCB surface). The plastic strip
consists of 3 laminations, interface in the perpendicular to the PCB
board. The outer laminations are translucent clear, and the center
lamination is dark grey. The other edge of the plastic strip at one end
contacts a flexible plated on mylar ribbon cable with 13 conductors and
silver or nickel plated contact surfaces. Next to the ribbon cable there
are no metallic contacts, but just a clear glass or plastic surface
which seems to have a ghost of contacts, or maybe just impression of the
plastic strip. This is the 2nd time I have cleaned the area with
tuner/contact cleaner and it works fine for 4 months or so with daily
use, and then the "start" button gets more intermittent. It seems to
work for a few cycles if one unplugs the unit briefly, and then you can
push the button all you want with zip. :(

I also scrapped a DMM recently that had a similar connector and display
problems.

Can someone explain the technology of this strange connection with 50
circuits on one side, 13 on the other along with a clear surface? And is
there something else I can do to improve the situation?  :)

2007\10\09@205927 by Robert Rolf

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The interconnect material is called "zebra strip" elastomeric connector.
www.neufeld.newton.ks.us/electronics/?p=167
"The anisotropic strip on the LCD is technically known as an
elastromeric connector, but usually referred to as a zebra strip. If you
examine it closely under a strong magnifying glass or a low power
microscope, you’ll see alternating bands of conductive and insulating
material, usually something like graphite loaded rubber for the
conductive material and unloaded rubber for the insulating material. The
graphite loaded rubber gives that portion of the strip a darker colour.
Thus, you have alternating light and dark bands, similar to what a zebra
looks like.  "


The 'ghost' connectors you are seeing on the glass display,
are indium tin oxide, which is conductive, and quite clear.

I think your issue may be insufficient pressure, so the contact
surfaces are oxydizing, rather than being sealed by the rubber.
A surface contact cleaner which leaves a residue (like NuTrol,
from M.G. Chemical) may work for you.

I too have had problems with DMM displays (notably two Beckmans)
with the exact same problem of display contact failure with age.
After trying to fix it for the forth time in 2 years, I bought
a Fluke, and have had no problems with the 6 or so Flukes we regularly
use in the lab.

R

PS. Don't buy an HP pavilion laptop. We have had 4 die on students
over the past two years, ALWAYS just past the warranty (1 year).
Dells seem to last forever. Compaq, so so. (sample size of about 130
over 5 years. YMMV).

Carl Denk wrote:

{Quote hidden}

> there something else I can do to improve the situation?  :)

2007\10\09@225350 by John Chung

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--- Robert Rolf <spam_OUTRobert.RolfTakeThisOuTspamualberta.ca> wrote:

{Quote hidden}

 Some of the Flukes do get oxidation on the LCD
connectors. Most of the successful reports use DeoxIt
solution for curing it.

John


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2007\10\10@091317 by David VanHorn

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Deoxit, available at Radio Shack, will do the job too.

2007\10\10@092615 by Carl Denk

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Thanks for the quick informative reply. Next time it is apart, I'll see
what I can do to increase the pressure, maybe bend a metal bracket or
shim somewhere. Are you saying that a cleaner that leaves a slight
residue is preferred? Or finsh cleaning with say pure alcohol, MEK, or
some other solvent. I picture the indium tin oxide on glass could be
somewhat fragile, and use of an abrasive is not a good idea. If in fact
it's oxydizing, I find it interesting that it is always the same
contact, though I can picture not being able to clean perfectly, and
leaving a crystal or something behind which becomes a seed for more
growth at the same location. As for sealing at the wire card edge, and
to a lesser degree at the mylar ribbon cable, the zebra strip doesn't
sit tight adjacent to the wires and plated contacts on the mylar, but
there will be a slight gap due to thickess changes.

Just read David Vanhorn's posting, I used Phillips ECG AC900-16 Tuner
Cleaner & Lubricant, the back says contains Isopropyl Alcohol and
silicone plus the usual propellent gases. Can I get a little agressive
on the zebra strip, or best to just light wiping with solvent and say
paper towel or soft cloth?


Robert Rolf wrote:
{Quote hidden}

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