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? How to reattach "zebra stripe" LCD connection in TI-30Xa?
Message #1 Posted by Paul Brogger on 9 Apr 2003, 1:58 p.m.

Off the wall, but a challenge . . .

I'm trying to resurrect a TI-30Xa calculator for my son (the one who WON'T use RPN). A few of the segments don't display in the middle digits.

Upon taking it apart, I see the LCD is connected to the PCB by a flexible multi-line connector that appears to be raised black conductors on a cream-colored "Scotch Tape" (mylar?) substrate.

It appears to simply be bonded to the surface of the LCD along one edge, and to the face of the PCB along the opposite edge. (Indeed, the LCD is attached only via this conductor, and is itself held in place against the bezel by a cushion and the calculator back case.)

By running my finger along the PCB attachement, I locate a couple (presumably) of conductors which are apparently not in contact -- when I press them, the seqments in question turn "on". When I release again, however, they go blank.

(It looks as if the PCB edge of the connector was slightly bowed as it was laid down, and contacts the PCB pads more fully on the left & right ends of the attachment, and less so in the middle.)

I'm wondering if anyone has a suggestion on how to reattach this flexible connector to the PCB traces . . . Is there a "conductive glue" or paint that might do the trick?

(Like I said, the challenge of fixing the thing is the issue, not what little value the calculator may ever have.)

      
Re: ? How to reattach "zebra stripe" LCD connection in TI-30Xa?
Message #2 Posted by Ron Ross on 9 Apr 2003, 3:08 p.m.,
in response to message #1 by Paul Brogger

Well you might try to just build up the compresioon side of the pressure plate with a little clear tape or clear epoxy paint(???).

On a side note, the Hp20s is far superior to the Ti-30 BS. Why sacrifice quality, even when you have to sacrifice RPN.

It is just such a nicer machine. That said, the Ti-30 series is a decent calc and is reasonalble and very easy to get. You might also consider the better Ti-36. Or even the new Hp9s.

Another calculator to consider is the BA II plus. Has better stats, has trig, and also has TVM so that Jr can learn the value of a $1 (well, okay, the value of $$$$). Of course you have to configure precidence.

I had same problem with a BA-35 and while I could fix some segments, others would then act up. I gave up after two attempts as I bought for only $2. used.

Great chance to aquire another calculator with everyones blessing. If he is into power pocket calculators, buy an Hp27s if money is not an issue (of COURSE I suspect it is). Actually, if he is in High school and they are going to require a graphics in the near future, the Hp 39G is selling awfully cheap (around $30-40 including S&H, of course they aren't all that great, but much more Horsepower than a Ti-83).

      
Re: ? How to reattach "zebra stripe" LCD connection in TI-30Xa?
Message #3 Posted by Ellis Easley on 9 Apr 2003, 5:04 p.m.,
in response to message #1 by Paul Brogger

That type of cable is generally called "flat flex cable". Sometimes they are made of copper strips with paper on both sides, like the ones that connect the HP97 printer. The ones used for LCDs nowadays are made of conductive ink on an insulating base and are attached with a conductive adhesive. The adhesive contains small conductive particles suspended in a gummy base so if two conductors are on either side of the thick dimension of the adhesive, some of the particles are in contact with both sides and the adhesive passes current, but the conductive particles in the space between the PCB pads aren't in contact with each other so there is no connection between the pads. BTW, Zebra strips (they have a fancy name I can't think of right now) are the three dimensional items consisting of a very tall many-layer sandwich of alternating conductive and insulating resilient material, the layers so small that there are several conductive paths for each PCB pad that the strip is in contact with. They have to be clamped between the two surfaces they are connecting, such as by the stainless steel frame that holds the LCD to the PCB.

I once repaired a multimeter that had the conductive ink type of flat cable by using some scotch tape to hold the flat cable to the surface and then using a length of drinking straw as a resilient strip pressed against the back of the connection. Luckily, the flat cable made a loop behind the LCD that held the tube in place when the unit was assembled. If that is not the case with your calculator, maybe you can stick the tube to the surface that sits behind the connection, using some double sided tape.


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