Re: TI-H: LCD Problems


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Re: TI-H: LCD Problems




I hate to burst your bubble, but you are describing the attachment of 
watch and simpler calc displays. VERY few graphic LCDs use zebra strips 
because the resolution is not sufficient. Most graphic displays, 
including ALL the TI graphing calc screens use metalized film plastic 
ribbon cable. It is a piece of plastic with strips of metalized film. It 
is not held on by pressure or some assembly, they are physicaly heat 
bonded to the glass and the PCB. I have re bonded them using a metal 
plate and a soldering iron, but they are so fragile, that I've only had 
50% success rate (I did 2 and one didn't work cause it came off within a 
few days). The other was succesful! Personaly, I'd prefer getting stuck 
with zebra strips because they are 10 times easier to fix than metalized 
platic film!

Richard Piotter
richfiles1@hotmail.com

Speaking of screens, I NEEEEEEEEEEED a TI-85 LCD for someone!!! (their 
metalized film died! =)

>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!
>



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