Re: TI-H: LCD Problems

To: ti-hardware@lists.ticalc.org
Subject: Re: TI-H: LCD Problems
From: Manfred Bartz <mbartz@werple.net.au>
Date: 24 Feb 1998 13:19:37 +1100
In-Reply-To: jdaomteys@juno.com's message of "Mon, 24 Feb 1997 15:18:53 -0500"
References: <19970224.151855.14430.0.JdAoMtEyS@juno.com>
Reply-To: ti-hardware@lists.ticalc.org

jdaomteys@juno.com (James Doty) writes:

> I dropped my TI-85 a while ago (REAL good for it!) and now the pixel rows
> on the left side of the LCD don't turn on unless I put pressure on it. 
> Right now I have a piece of paper wedged between the top of the LCD(where
> the wire-tape joins it) and the case, but that can get real annoying when
> the paper shifts and the screen doesn't work. Anyone know of a more
> permenant solution (without paying TI the frikking $70 for repairs!)?
> Thanx

James, a few days ago this question was asked on a related list, so
here is a copy of my reply to that one:

Joe <...> writes:

> I accidentally dropped my 86 today.  I knocked it off of my desk at school.
> When I picked it up the first 9 columns of pixes had disapppeared.  I havn't
> noticed any other side affects yet, except that I can't see what I am
> typeing part of the time.  if anyone knows how to fix this please respond.
> My warranty on it has ran out, so I can't send it back to TI, unless I pay
> them for the service on it.

Your chances of repairing the calculator yourself are about 1%.  Send
it to TI and get it fixed!  Fiddling with it yourself is likely to
make matters worse!!

What?  You are still reading?

OK, I have not looked specifically inside a TI calculator, but LCDs
are generally mounted in the same way.  It is useful to understand the
principles before you attempt a repair.

The actual display consists of a liquid crystal contained between two
glas sheets.  The glas sheets have very thin, transparent metalization
much like the tracks on a printed circuit board (PCB).  Trying to
solder to those tracks will destroy them.  Any scraping will destroy
them too.  The electrical connection from the glas sheets to the PCB
is made by "zebra-strips".  These are strips of rubber shaped like a
ladder.  When the LCD is assembled, you look at the side of the
ladder, the rungs are hidden.  The rungs of the ladder are conductive
(not as good as metal but enough for the few micro Amps needed to
drive the LCD).

Glass sheets:  ==========================================
Zebra strip:   ||||||||||||||||||||||||||||||||||||||||||
PCB:        -------------------------------------------------

This assembly is usually held together by some plastic or metal holder
that presses the glass sheets against the PCB, compressing the zebra
strips slightly.  This may be an integral part of the calculator case.

So, what happened when you dropped the calculator?

In the worst case, the glass may be broken, or the two sheets may have
come apart or un-sealed.  This is unlikely in your case because it
still works partially.  However, DO NOT GET THE LCD LIQUID ON TO YOUR
SKIN!  I am shure it isn't healthy!!  Repair is not possible in this
case.

More likely, the glas sheets moved a bit inside their holder, shifting
relative to the zebra strips and/or the PCB.  If you are really extremely
good at repairing small things (like fixing old fashioned, mechanical
watches) you could try to nudge the zebra-strips a bit if you can get
to them.  It may also be possible to remove the LCD holder and
repositioning the glas sheets and zebra-strips.  You need to work with
very high accuracy.  Do not touch any of the contact areas, human skin
secretions are highly corrosive!

Good luck.
--
Manfred Bartz  <mbartz@werple.net.au>
-------------------------------------
Tell me and I will forget,
  Show me and I may remember,
    Involve me and I will understand!

References:

TI-H: LCD Problems

From: jdaomteys@juno.com (James Doty)