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I have Samsung Spica I5700 that have capacitive touchscreen, and I used a touchscreen protector.

Recently, I've noticed that the touchscreen often produces erratic movements, for example, if I put my still finger on the screen, the "cursor" will shake vigorously (sometimes very far off).

This makes the touchscreen very unusable; countless of times I've accidentally flinged the page when scrolling, while touching the screen for small scrolling; countless of times, the screen registered scrolling as a zooming or unzooming; and worse, it often flings to the wrong direction from my swiping direction (indicating a random erratic sensing). Sometimes, when I tried to touch a button/link on the top-left, the screen will detect a click in some other far away button (i.e. one not under my finger). Any games that uses touch intensively also becomes unplayable.

Could this be caused by the screen protector? Since capacitive touchscreen is operated by soft surface of a finger (instead of a pointy stylus), is there any noticeable benefit of using screen protector? or are they just a waste of time and money? do you think peeling off the protector will have a chance of fixing those problems?

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Does it do this all the time or just when it's plugged in or tethered to the computer? I was having the same problem with my Droid on 2.1, but only when it was plugged into my computer via the USB cable. I've had a screen protector on since day one (with the exception of a few days here or there) and I have not had any problems with it. It very well could be the cause of your problems but they are well worth using to protect the screen from scratches. I recommend removing yours as a trouble shooting method. –  Matt Oct 2 '10 at 8:58
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Have you tried running through screen calibration? –  gary Oct 3 '10 at 1:09
    
@Matt: I'll check the effect of plugging when the screen goes awry again. I noticed that the screen is often to be worse off when I'm using the phone inside my room, compared to when I'm outside (maybe the temperature, or humidity, or maybe because it's not plugged in). It seems improbable plugging in could affect the touchscreen, but we never knows. –  Lie Ryan Oct 3 '10 at 14:51
    
@gary comtois: Either Spica doesn't come with a screen calibration, or I can't find it I can't find a calibration app in the market either. –  Lie Ryan Oct 3 '10 at 14:51
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@Matt: Confirmed: after installing a screen testing app (and subjective confirmations on other apps); I found that the touch becomes most shaky when I'm plugging into my laptop which is itself connected to the wall charger. The touch is less shaky when the laptop is running on battery or when the phone is directly charged on a wall charger, but they're still not as stable as when the phone is free-standing. This makes me suspect that this is probably some electrical or grounding issue. Since the touchscreen protector is now freed of all charges, I think I'll open a new question sometime soon. –  Lie Ryan Nov 18 '10 at 11:41

3 Answers 3

up vote 4 down vote accepted

To answer you questions:

Could this be caused by the screen protector?
Possibly. Take the screen protector off and see if the problem persists. My screen protector doesn't affect the functioning of my screen at all. This is going to depend on the particular screen protector (I'm sure there are cheap, bad ones) and the particular phone (they all have different screens and some have calibrations, some dont, some have screen sensitivity adjustment options, some don't).

Is there any noticeable benefit of using screen protector? or are they just a waste of time and money?
Yes there is a benefit, they protect the screen, and no they are not a waste of money. I have scratched/scuffed the hell out of my screen protector and all I had to do was remove it, and put a new one on and my phone was as good as new. Had I not had a screen protector my phone would be unusable now, so for just a few dollars and no performance cost my phones screen is as pristine as the day I got the phone. That being said, my job and my lifestyle tend to put the phone through a lot of abuse ;o)

My recommendation: Take the screen protector off and go from there. If that doesn't work and it's under warranty, bring it back.

There are so many factors that can affect the touchscreen because it is the basis for all inputs and outputs of the device and troubleshooting can take a while. I would be surprised if it was the humidity or heat difference between indoor and out, but there are a number of different things that can change from indoor to out and if theres a bug, they may be affecting how your phone operates: GPS, Wifi, reception, Auto-brightness sensor.

This correlation could also be a coincidence. It could be a particular app that isn't playing nice with Android and your phones firmware.

You will need to to systematically isolate the conditions that affect the problems with your screen and the ones that don't, but ultimately it could just turn out to be a bad unit.

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Note that you have scratched your protector, not the screen. That's because screen protectors are made of soft film susceptible to scratching. Just remove it and enjoy scratch-free uninhibited clear view - free of charge and for the life of your device. –  Alexander Shcheblikin Dec 17 '12 at 18:24

Screen protectors seem to have no effect on touchscreen sensitivity.

I carry my phone in a small thick clear plastic bag. Sometimes I take the phone out to operate it but more often I don't - and it works beautifully.

The problem you have is more likely to do with parasitic capacitive coupling sneaking in from somewhere in your setup.

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The problem

if I put my still finger on the screen, the "cursor" will shake vigorously

can be caused by the power supply. Touchscreen sensors seem to be very sensitive to power supply ripple. It is easy to check; unplug the power cable (on a phone this is usually also the USB cable) so that you are running from battery, and see if the problem goes away. Be sure your wall charger has enough power (check the output current against the phone/tablet spec).

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