Power related touchpad woes continue...

Discussion in 'Lenovo IdeaTab A2109' started by arbarnhart, Feb 5, 2013.

  1. arbarnhart

    arbarnhart Senior Member

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    I may be sending it back for warranty service (more likely replacement). Last night, I connected it to a powered USB hub and got the behavior I have seen a couple of times from having the wall charger on a car inverter. The touchpad starts registering incorrectly. In portrait mode, trying to use a soft keyboard it will get extra characters that are usually on the same row. It was practically unusable right after it happened, but by this morning it was almost normal again (was still getting a few extra, but not as bad as before). I suspect that tonight it will probably be okay again. The input technology is "capacitive" which likely means there are capacitors involved; the only explanation I can think of for it stabilizing with time is a capacitor slowly dropping voltage after a spike.

    Am I the only one that has seen this issue? I did some Googling and found this is a known issue with some noteboook touchpads, which are also capacitive.

    Assuming it returns to normal, I may just have to accept that it can only be charged by clean wall power using the provided charger or from a computer (I have done that without trouble). But I am not sure; mine might be an anomaly. I would hate to go the trouble of trying to get warranty service only to find they all do this. I am not even sure how much luck I would have with service if the problem resolves itself in less time than it would take to get it to a service center. I will follow up later to verify whether or not it resolves again.

    Other suggestion? I have looked at surge protectors that have USB outlets, but I don't know if that would help.
     
  2. arbarnhart

    arbarnhart Senior Member

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    It has partially recovered - the touchpad works fine now when it is disconnected but still glitches, though not quite as badly, when charging (and I am using the supplied charger). I expect that tonight it will probably be back to normal. If it is, the question becomes whether all units do this or whether this is a bad unit. In an odd way, I almost hope it stays glitched while charging because then I would be able to get it replaced. Has anyone used an inverter (car 120V AC converter) with success to power the unit via the included wall charger? Anyone with an inverter eager to test? I didn't think so...
     
  3. arbarnhart

    arbarnhart Senior Member

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  4. arbarnhart

    arbarnhart Senior Member

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    A sampling of a few posts that I think are related for the curious. I would really appreciate it if someone with good working knowledge of this type of electronics weighs in. At present, it works fine off battery but the touch pad is difficult to use if it is charging; even from sources that used to be okay. Is there a simple way to disconnect the battery and let the internal components completely drain? My limited knowledge of capacitance makes me suspect something still needs to discharge. The good (sort of) news is that nearly everything I read reports usage problems that do clear up without permanent damage.

    Power inverter freaks out my touchscreen
    Loss of touchscreen function when charging from inverter in car
    iPhone 4 Multi Touch Issues when Charging In a Car - MacRumors Forums
    Laptop touchpad unusuable when on AC power (via inverter) in vehicle
     
  5. WasteLandSavage

    WasteLandSavage Senior Member

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    OK just food for thought.
    I just ordered my A2109 yesterday.

    BUT this problem may or may not be with your hardware and here's why.

    I am typing this right now on my Iconia A500 running ICS, And when I hook a Bluetooth Keyboard to it it will type along just fine for awhile minutes, hours or days.
    Then as you say it starts with a lot of phantom key presses wither I'm touching my keyboard or not.
    Wither it's powered or on battery. Sometimes it will stick so bad that even after I shut off the keyboard it will keep going with a line that looks like this.

    hhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh

    Here is a link to a thread I started about it It maybe of some help.

    http://www.androidtablets.net/forum...rd-stutters-iconia-a500-loses-connection.html

    I am typing this on a wired usb keyboard and at times as well for no apperant reason it's keys will either do a quick stutter or some maybe completely unusable until after I restart my tablet..

    The research I've done says this is a well known problem with ICS itself.
    And very few have found away around it pertaining to specific models wither it be phones or tablets.

    I have no idea if your running ICS or JB?
    But I hope it's not the same in JB or I'm in for a wild ride trying to get it to work on my bluetooth keyboard since I really will have no way of leaving my wired keyboard hooked up to it while at my desk.

    Hope This Helps. Ricky
     
  6. arbarnhart

    arbarnhart Senior Member

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    I am running JB. My research indicates that using an AC2DC converter powered by a DC2AC inverter often causes problems with capacitive input devices. Typing with BT keyboard or using a USB mouse both work fine while it is having trouble. The real message is don't use an inverter in a car or you may put the tablet at risk. I am still hopeful that my problem will resolve itself. I am using a soft keyboard (SwiftKey Flo beta) now and it is working properly. But I am using battery power only. I charged with the tablet completely powered off last night.
     
  7. WasteLandSavage

    WasteLandSavage Senior Member

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    Well I have never had a reason to use a power converter in my car as most times I'm only using mine at home.
    Now sometimes when we are out my wife will use her iconia a500 but we have never used it on a converter so I can't comment on what it would do.
    Although you did ease my mind about the bluetooth usage on the A2109 not having the same troubles as my iconia has, for sure it won't if they both work fine while you are having this trouble.

    Since you are using another virtual keyboard of sorts and it is not giving you any problems like the oem one is.
    Maybe a Factory Reset would fix it?
    It might just be possible that something in the programing got fouled up a bit when you tried using the converter in your car.
    Although it shouldn't effect it, I would say it is possible since another softkey program is working without any problems.
    I seriously doubt it's any of your hardware.

    Let us know how it goes. Ricky
     
  8. arbarnhart

    arbarnhart Senior Member

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    When the touch is screwy, no soft keyboard works. In fact, one of the clearest illustrations of it (literally) is to open a drawing program and randomly poke the screen, which should result in a bunch of dots. When it has the problem, many of the dots will be horizontal (in landscape mode) lines. All programs system wide have trouble. If you check some of the links I posted earlier about completely different tablets and systems, it is all pretty much the same underneath. Capacitive touch is extremely power sensitive by its very nature. Capacitors hold a charge for quite some time, so once you get it screwy it can take a while to clear up.
     
  9. WasteLandSavage

    WasteLandSavage Senior Member

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    OK another wild idea.
    I understand what your saying I misunderstood your previous post Sorry about that. :eek:

    OK here's the idea sometimes on a laptop the circuits will get a static charge causing glitches system wide even to the point where they won't boot at all.
    So to fix the problem you take out the battery and unhook the power supply, Hold the power button for 10 to 30 seconds.
    Put the battery back in and reconnect the power and that clears it right up.
    I haven't had that problem much but it has happened and that has always fixed it!

    Now since you can't remove the battery, You may want to try running the tablet completely out of battery power where it shuts down itself.
    Hold down your power button for 10 or so seconds then plug the power back up and try it and see if that fixes it.

    I know tablets and laptops are different animals, but the principal is the same.
    It's just dumb enough to work.
     
  10. arbarnhart

    arbarnhart Senior Member

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    Powering off, not just suspending, seemed to fix it. But it took a couple of nights. I am not going to use the inverter to power it ever again. I am planning to get one of those Trent USB battery packs for long trips.
     
  11. WasteLandSavage

    WasteLandSavage Senior Member

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    Good to hear.
    Just suspending allowed a certain amount of power to remain at all times on your tablet.
    But completely powering off cleared out any power whatsoever and allowed the capacitors to completely discharge although it may have taken a couple of nights.

    In the same basic principal did exactly what I was explaining.
     
  12. arbarnhart

    arbarnhart Senior Member

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    I just talked to a friend who is an EE. He summed it up pretty well - "On one end is a connector originally designed to produce incendiary heat and on the other is a connector originally designed for serial data transfer." His suggestion is to get a good USB car adapter instead of a no name eBay special. He echoed the sentiment that inverters are a bad idea.
     
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  13. vampirefo.

    vampirefo. Senior Member Developer

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  14. arbarnhart

    arbarnhart Senior Member

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    I followed up over there. I think what we have in common is that at some point the power provided to the unit was out of spec. I am still a little annoyed that the supplied charger doesn't have some protection against that, but a friend who knows electronics better than I tells me that it is harder and more expensive than I think. The chargers are built to assume reasonably close to spec AC and if it varies much, the supplied DC will vary. DC to DC is much easier and the better car USB chargers do deliver clean power (again, 2nd hand info).
     
  15. drcrash

    drcrash Member

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    A note about (DC to AC) power inverters: don't use them with fancy electronics unless they're the expensive "true sine wave" kind, or you know your (DC to) AC adapter can handle weird waveforms. Many cannot, including the inverters in cheap UPSs (uninterruptable power supplies).

    Normal AC wall power is a very smooth sine wave, with the voltage smoothly increasing and smoothly decreasing then doing it the other way, over and over. It contains energy at only one frequency (60 Hz in the US, 50 Hz in lots of other places), aside from hopefully minor noise.

    What normal inexpensive inverters put out is something very different---a very crude, blocky stepwise approximation of a sine wave---it only has a few voltage levels, and jumps from one to the next suddenly. This is bad, because it is not what many electronic devices are designed to expect and A SURGE PROTECTOR WILL NOT HELP WITH THIS AT ALL. (Surge protection has nothing do do with this. A surge protector kicks in when the voltage gets out of bounds. This isn't about very high voltages, but about sudden changes in voltages that are within the general bounds of the sine wave being approximated.)

    When you have a crude stepwise approximation of a sine wave, it has energy at 60 Hz, but not as much 60 Hz energy as pure sine wave, and some of the energy is at multiples of 60 Hz, especially 120 Hz and 180 Hz, but going much higher than that too.

    There are two common kinds of AC-to-DC power adapters to run electronics, and neither can be trusted to deal with this weirdness unless you know it was designed to do so.

    1. An old-style (heavy) dumb transformer will just lower the voltage of the input waveform by a constant factor, but output a reduced-size copy of the same messed-up approximation of a sine wave. Unless there's circuitry after that to smooth it out into a close approximation of a sine wave, whatever's actually using the power may malfunction.

    2. A modern (lightweight) high-speed "switching" power supply works differently, but may have much the same effect. What it does is to switch the power on and off very, very fast, many thousands of times a second, with it off most of the time, so that the voltage over any significant period of time (like a millisecond) averages out to what it's supposed to be. For example, it might turn the power on for a microsecond every ten microseconds. That's a very messed up waveform, but just a little smoothing (at a scale of about a millisecond) will make it come out very smooth, and an almost perfect sine wave.

    If that's all your switching power supply does, though---turn the power off 90 percent of the time, say, it too will output a scaled-down copy of whatever waveform you put into it, so if you've got a squared off approximation of a sine wave going into it from an inverter, you'll get similar garbage coming out.

    A fancier switching power supply can cope with this by changing the scale factor (what percentage of the time it's on) a bunch of times in every 60 Hz cycle, so that where the input voltage is too high, it will switch it off a larger fraction of the time, and where it's too low, it will switch it on a larger fraction of the time, and will probably need bigger capacitors to store some charge for the times when the input voltage is just too low (e.g., staying zero for a while before jumping up).

    Because most people don't understand these issues, power supplies are generally not labeled or marketed as being able to do this, even if they can---most people wouldn't understand the issue anyhow, so they don't talk about it. If you want to know, you likely will have to call the manufacturer.

    Some inverters and some UPSs are marketed as putting out a true sine wave, but the ones that don't are generally not labeled either way, so your best guess is that if they don't say, it doesn't. (Especially if the price isn't high.) Look for one that does before plugging random electronics into it, and expect it to be more expensive.

    I don't know if the inverters specifically marketed as being good for plugging computers into them generally put out a decent sine wave, even if they don't say so. I would hope so, but I would guess many don't, just like cheap UPSs. (Including major brands' lower-priced models.)

    I think it should be quite illegal to sell either without a warning about this issue---you shouldn't be able to label something as outputting 60 Hz AC at a given voltage unless it only puts out a pure 60 Hz sine wave, not a mess with some of the energy at 120, 180, and so on---but it's not.

    Caveat emptor.

    -- Crash

    PS. You might wonder what cheap inverters are good for, and the answer is basically resistive heaters and incandescent light bulbs, and many cheap electric motors, used lightly. Resistive heaters and incandescent lights aren't much bothered by non-sine waveforms, so long as the average and maximum voltages are about right. Many motors---e.g., in your electric shaver or power drill---do okay with an approximate sine wave, but many don't do quite as well as with a true sine wave. Depending on the design of the motor, they may do just as well as with a true sine wave, or they may only use the power that's at 60 Hz, and the other frequencies may end up creating hums and heat rather than rotary motion---so they're a bit underpowered, and may tend to overheat if you use them for too long at a stretch.
     
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