Kindle Fire 1st gen, absolutely no touchscreen response, it's frozen

[ivan747]

Hi guys, I wanted to ask anybody with experience on capacitive touchscreens about this:

Before trying anything, I wanted to ask you if you have had an experience with capacitive touchscreens that do not respond, and specifically, the case of the Kindle Fire 1st generation.

More than a year ago this Kindle started to develop a problem in which it registered touch events when there weren't any. Sometimes I would touch the center of the screen and also get input on the corner of the screen, for example. After this, it began to miss touches in a section of the screen. Eventually, one day it decided not to get any input at all. When I bought it it was always a bit too sensitive.

So I charged up the battery to roughly 50% and stored the thing for a long while. Now I kind of want to use it again. I have tried plugging and unplugging the touchscreen flex, I disassembled the Kindle to inspect the touchscreen digitizer and nothing looks obviously wrong. The flex cable has a chip soldered on board as well as some other passives and a couple of sot23 packages. I tried putting some pressure on those just to see if the problem was solder joints, but nothing.

I kiiinda got it working for a fraction of a second making a lot of pressure on one section of the digitizer, with the Kindle assembled, but I can't replicate that.
I tried putting it in a dry, cold environment. No change. Before that, I tried heating the digitizer a bit with a hair blower, nothing either.

A new digitizer is $17, and perhaps I could buy one.

[tautech]

If when you pushed firmly you were not making contact with leads or pads of any components I'd suspect a failed solder joint.
Very carefull magnified inspection might find it, especially if it has any current to speak of through it.
Look for a grey smudge or crack.

I had a SMD & TH PCB some years ago that drove me mad trying to find a cracked joint that I knew was there. Flexing the PCB can produce a click-clack signifying a cracked joint.
In that case a total resolder fixed it.

But it seems you already have a possible area to concentrate on....good luck.

[ivan747]

We'll see... I'll try a visual inspection of the flex, and a visual inspection of everything that leads to the touchscreen connector on the motherboard.

A brute force aproach would be reflowing these areas with hot air, right? The problem is, I don't have a hot air rework station, and for what is worth, I can buy the digitizer for this and an upper screen for a Nintendo DS I also want to fix. I can also try with a soldering iron, of course.

[amyk]

Could be the bonding of the flex to the digitiser glass ITO.

[ivan747]

Could be the bonding of the flex to the digitiser glass ITO.

Is there a fix for that?

I'd really appreciate a clean room (as in dust-free) when working with this sort of stuff 

[amyk]

I think they're usually bonded with a hot-bar type of process, so theoretically you could rebond it/use ACF, but that's not an easy fix. You could disassemble enough to get to the connection and then press on it to see if that is the problem.

[ivan747]

Sounds like it. I'll give it a try.