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Weird Touchscreen calibration problem

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Karpour Page Icon Posted 2015-10-21 1:40 PM
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I'm fairly sure it can't be repaired, but I wonder if anyone ever encountered this problem with a touchscreen (see attached image)
All the touch input is distorted, after quite some testing and connecting the touch panel directly to a microcontroller I found out that the touch panel itself was the cause of the problem and not any of the electronics in the tablet (I found suggestions checking for leaky capacitors or the CCFL inverters)

Anyway, after some more research I found some sources that say that the 2 layers of the resistive touchscreen can come lose and not work properly anymore after a while.
I saw some people fix this with heat to "bond" the panels again, but I am pretty sure there is a 90% chance I'd destroy the panel trying that, so I'll return the SimPad to the seller, who offered me a full refund and assured me he wasn't aware of the defective touch screen.



Edited by Karpour 2015-10-21 1:41 PM




(simpad.JPG)



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Attachments simpad.JPG (55KB - 0 downloads)
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Rich Hawley Page Icon Posted 2015-10-21 1:49 PM
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One thing that can happen is that debris builds up under the edge of the front case between the touchscreen and the bezel border. You might try taking the case apart and cleaning that area and see if anything happens...but I've never seen the problem you show in your picture...I assume that each of the lines was supposed to be a parallel vertical line from top to bottom and it distorted while drawing it?

Kind of reminds me of those funhouse mirrors that hourglass your image....
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Karpour Page Icon Posted 2015-10-21 6:45 PM
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Yes, those were supposed to be straight lines.

I don't really think it's dust since the two planes should be press much completely sealed off.
I've seen videos of using open fire to successfully fix a touchscreen, but yeah.. that's too dangerous, I'll continue my search for a working SimPad because from what I could try, it's an amazing device!
I might do a little review, it's really nice to have such a high resolution, it also feels much more snappy than for example my J720!
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Rich Hawley Page Icon Posted 2015-10-21 6:56 PM
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If you want a tablet, you should check out the NEC Mobile Terminal on eBay....that's a great price for a CE5 tablet with built in wifi.

http://www.ebay.com/itm/NEC-S1596-01-MOBILE-TERMINAL-W-DIGITIZER-TO...
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Karpour Page Icon Posted 2015-10-22 2:14 PM
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Thanks for the suggestion, sadly it's hard to get those NEC tablets over here in Europe!
I found another SimPad in the Netherlands which should hopefully work, so I'll try that for now. I assume that even on WCE 5.0 there isn't too much everyday-stuff you can do anymore, I mostly like running old Software and writing my own applications with PersonalJava
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Rich Hawley Page Icon Posted 2015-10-22 7:39 PM
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Oh I don't know...you can still do plenty with these old tablets...such as

1) Ebook readers
2) Play games on them.
3) Surf the web (if the site isn't too intensive)
4) Use them as a GPS (with CF receiver)
5) Doodle pictures...way better than an Etch-a-sketch
6) Use them for video presentations/kiosks

and I'm sure there are a bunch of other things they work well for...
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Karpour Page Icon Posted 2015-10-28 6:10 PM
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Oh ffs..

I bought another one.. same issue.. not as bad, but still unusable, even though I specifically asked the seller to check the touchscreen and he assured me it was working perfectly.

I guess I'll give up trying to source a working SimPad..
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Alt Bass Page Icon Posted 2015-10-29 8:05 PM
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Can't you find the touchscreen with similar size? They all have same protocol and 4 wires.
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Karpour Page Icon Posted 2015-10-29 9:27 PM
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That was my thought.. the second seller has no intent on taking it back, so I'll take it apart and try to find a matching touch screen.. I already have some candidates on ebay, just gotta make sure they match.

I measured the impedance though, and they were around 2k per axis on the SimPad touch panel, while most I've seen sold had more like 200-400 Ohms. I hope the controller doesn't expect a specific range, but otherwise this should work.

In case I manage to repair it, I'll write an article as I'm sure there are other people with the same issue.
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Rich Hawley Page Icon Posted 2015-10-30 12:41 PM
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Most resistive touchscreens have the impedance in the 10-15 MOhm range. The really old machines, pre-2002 went a little lower because of acrylic properties of flexibility. But there is only one way to find out, and that is to give it a shot. I still think that maybe dismantling your device and cleaning the touchscreen and the ribbon contacts may make a difference...normally either these things work or don't.

The fact that you get that weird pattern suggests to me that something (ie debris in front of the touchscreen, but under the edge of the bezel) is affecting calibration.
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Karpour Page Icon Posted 2015-10-30 2:05 PM
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Well, 2k was what I measured.

Thinking about it though, Touch panels work with a voltage divider principle, so basically the impedance should be pretty much irrelevant to the controller IC.

Anyway, I'm returning one SimPad, the other one is in the Netherlands atm, it'll take a while until I'll be there again to pick it up and am able to order a fitting touch panel (if I find one)
If the fix works, that would be pretty exciting news though!

Really curious if any of the SimPad owners here ever experienced similar issues. I mean 2 devices I bought had the problem, and the only 2 other listings I saw for them mentioned that the touchscreen calibration didn't work properly anymore. So clearly this must be an issue that affects quite a few SimPads!
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arlex Page Icon Posted 2015-11-01 8:23 AM
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Quote
Karpour - 2015-10-30 9:05 AM

Really curious if any of the SimPad owners here ever experienced similar issues. I mean 2 devices I bought had the problem, and the only 2 other listings I saw for them mentioned that the touchscreen calibration didn't work properly anymore. So clearly this must be an issue that affects quite a few SimPads!


My SIMPAD SL4 that I have bought as s/h 1 year ago is still looking good. Unfortunately I did not manage so far to burn a newer image in English over the German original OS. It is a pity that these Win CE3.0 machines do not have a shut down button because in suspend mode the battery cannot preserve the charge and it is running down quickly.
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arlex Page Icon Posted 2015-11-02 4:57 AM
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Karpour, you have a PM.

Edited by arlex 2015-11-02 5:05 AM
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Krzysz Page Icon Posted 2019-03-19 3:56 PM
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After reading this thread, I was pretty sure that this is a fate of all old SIMpads. So I was certain that my newly-bought SIMpad SLC would have not-working touchscreen as well. But to my surprise, everything is allright, at least in regards to touchscreen (I don't know why, but I strongly prefer resistive touchsreens over capacitive ones. Navigating Windows with capacitive touscreen (for example on my HP Stream 7) is a nightmare, while on my Fujitsu Lifebook U810 it was pretty doable, even without a stylus).

6€ for a Siemens SIMpad spent in a quite good way (+another 6€ for combined shipping together with some other old crap).
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Karpour Page Icon Posted 2019-03-26 7:49 AM
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I recently got a SimPad SLC after my futile repair attempts, the touchscreen does work there. It seems to be that only SL4 models are using the faulty model
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