Restoring touchscreen functionality

[Markismus]

A year ago I cracked my Note Pro. The cracks have gotten worse and worse and today I finally removed the glass covering the other layers of my Note. (See 1st thumb.)

A side effect of removing the glass is that the touch function stops working. Not the pen, however, which is working via the Wacom layer.

So remembering the Kobo Glo, Aura HD, etc. with their plastic guide for the touchscreen, I experimented with a transparent screencover and relective alumnium tape (thumb 2) and with black plastic isolation tape (thumb 3 and 4). No success, though.

So the current functionality for touch is that I can touch the bottom of the screen and it registers. So in Koreader, I can dis-/enable the mini status bar.

Does anyone know how the touch functionality on the Note Pro works? Does anyone have a hunch how to fix it? Would anyone know how to get a replacement glass?

[Renate]

Mmm, I'm no pro at display internals (despite destroying one or two myself) but I think when you pulled up that outer layer you also ripped up all the transparent conductors that are used for the capacitance layer. https://en.wikipedia.org/wiki/Indium_tin_oxide You can see the "fan-out" at the bottom, about the same as the eink. There are three chunks for left rows, columns, right rows. Since everything is ripped up it's lucky that a few spots near the bottom work.

You can try my UsbMode.apk (in my sig at my website), which among other things will show you touches by coordinates. Or you can go to Developer Options and turn on touches or coordinates.

Unless the factory has a repair plan I'm not sure that you're going to find a replacement screen.

[Markismus]

Thanks for the response, Renate.

What did you mean with 'fan-out'? The black half-triangles in the corner and the triangle in the center of the bottom.

Thumbs 3&4 show the coordinates from the developer options.

Would the indium-tin-oxide layer reflect IR or conduct electricity? Has the Note Pro a capacitive touchscreen or adaptive (IR) touch screen? Capacitive touch, indeed.

[Renate]

Yeah, usually a flex printed circuit (of Kapton, the orangy yellow stuff) plugs into the main board. It might have ~8 contacts and uses I²C interface. It feeds an IC mounted right on the flex that drives 50-100 axis lines. The end of the flex goes to the display and transitions to silver ink (which you can see) that transitions to ITO (which you can't see). You have your finger on places which are still silver ink, so it will work.

The Eink display itself is similar, but at a much higher density of 300 DPI. The capacitive touch only needs to be ~6 DPI since it can interpolate.

[Markismus]

I'll have to go and have another look, 'cause I didn't see the tag. Maybe, it's connected to the back of the PCB. However, they aren't in the Kobo's and the tablets that I opened.

Hope that you're right, of course. Within 20min I found this digitizer with dimensions 17.3cm x 22.5cm Given that the Note Pro measures 17.2cm x 24.4cm, it would leave me room for the bottom button but I would have to sand off the black plastic ridges at the sides. (Resistive technology, though, so that's not perfect.)

[Renate]

Those photos are not your model, only the Nook Glow 7.8".

[Markismus]

I know.
What I meant was, that when I removed the glass from my Kobo Aura (a long time ago) I cut through the tag and realized I was f*cked. However, I didn't stumble on (the remains of ) a tag this time, yet.

Apart from the glue layer, on top of the Wacom layer, (that had to be warmed by a heat gun before I could remove the glas shards,) there was no connection other than an extra glue strip over the black inserts in the iron.

That's why I did the experiments.

Another reason is that the screen was _very_ heavily cracked and the touch functionality remained. I don't expect that if it was a conducting layer created by vapour deposition. However, the conducting layer was against the glue layer, so maybe it didn't crack.

One thing I do really like, apart of the disappearance of all cracks, is the weight: The Note Pro without a glass layer is really light! So I will have to make sure to get a light plastic digitizer. I don't want that weight back in my hands.

[Markismus]

So I opened it up again and I uploaded a photo of the PCB on the back.

On the top of the PCV there are two headers with flex-strips. The left one is not in the picture, because I damaged the power button. The right one goes to the Wacom layer.

On the bottom there are 3 flex connectors. Left is for the Eink screen, the middle one for the LEDs of the frontlight and the right one is for the capacitive touchscreen. (See thumb #2. 7-pin connector. On the strip there is the string "LX-103VIP01GT1" and on the backside right bottom of the touch screen is the string "039-01A1 103TPV2". Touchscreen width x length = 16.45cmx22.2cm and touch screen area is width x length = 16.15 x 21.5. Searching with Google nor AliExpress got no hits.)

So why would the touch screen not work anymore except at the bottom? Could it be that I damaged the strip? Could it be that the touch screen fails when you heat it enough for the glue layer to melt?

[Renate]

Originally Posted by Markismus

So why would the touch screen not work anymore except at the bottom?

Umm, because you destroyed it? You ripped it to shreds?

Do you have any of the glass that you broke off left?
You can use a meter and see if you can find any conductivity on the inner side.

[Markismus]

I got three reasonably large shards from the bin. I set my multimeter to Ohm and measured no conductivity whatsoever between glass-glass, glue-glue and glass-glue. The plastic layer to which the flex connector is attached is unbroken. (See thumb #1, post #1. It's the layer with the rectangle of wiring on it.)

If you open up that image in another tab, you can zoom and they only thing I can see are some small dents made during shard-removal. The dents on the flex wire are especially worrisome.

[Renate]

Well, I can't see where the layers are here. I would presume that the ITO was on the back of the glass. I've never measured it personally.

You can see where the pads are for the two axis. Have you tried touching an X and a Y? Have you tried with some insulation between you and the two touch points? Have you looked for continuity on the layer that you have left?

[Markismus]

I finally read the relevant wiki's. Learned 2 things: 1) The scratches on the plastic layer are not relevant, because it has to come off anyway. 2) I should have used a cutting wire to separate the layers. All the other information was really already provided by you.

So II'll have to find a fitting capacitive touchscreen and get it to work with the Note Pro. A resistive won't work be cause it will interfere with the Wacom layer.

[Markismus]

I had no luck finding fitting capacitive panels on AliExpress or eBay. Does anyone know where else I could look?

[Renate]

I wouldn't think it would be too easy to put on another panel without some new glue and some sort of hot press. Even then I'd think you'd have to remove the entire Eink panel to really do it correctly. I'm not trying to be negative, it's just that you've got a clean, half functional thing now.