Author Topic: Touchscreen wobble (cleanup of thread)  (Read 16111 times)

Destroyer

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Touchscreen wobble (cleanup of thread)
« on: January 26, 2011, 12:48:59 AM »
OK,
Many of you may have a Freescale A8 product  with a serious wobble on the screen interface , when you touch it.

For all people not following this fiasco from the start:
This is the thread that clarifies the information:
Currently we have Three sources for the information:
Slatedroid
http://www.slatedroid.com/index.php?topic=13847.0
http://www.slatedroid.com/index.php?topic=15127.0

The Russian site (Smartqmid)
http://smartqmid.ru/index.php?showtopic=1957&view=findpost&p=24324

This site
http://hardcoreforensics.com/wp/forum/index.php?topic=73.msg245#msg245
http://hardcoreforensics.com/wp/forum/index.php?action=downloads;cat=11

The fix proposed is not the best way to do it, but it seems to work for the most number of people

If you go here: I/O interface board, you can see both sides of the PCB we are talking about,
you can also see the 4 Capacitors on the PCB C83,C84,C86,C87
A circuit diagram is HERE

The capacitors that need to be 'piggy-backed' are:
  • C87, do this one FIRST if it solves your problem then you are good to go.
  • C84, if changing/modding C87 did not solve your problem then do this one as well


Actual Value
The actual value will depend  both on the touch-screen noise source and the values currently used for  b]C84, C87[/b]

The Russian site has had good results with the following values:
22nf (223)
33nf (333)

My pad works fine with:
47nf (473)

So that gives us a suitable working range of values , you can go as low as 10nf and as high as about 100nf, going much higher will start to affect the accuracy/response of the touch screen.

Please feedback your results so that we can draw up a table and analyze the best components to use.





« Last Edit: January 26, 2011, 09:14:18 AM by Admin »

willumpie

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Re: Touchscreen wobble (cleanup of thread)
« Reply #1 on: January 31, 2011, 08:55:27 AM »
Hi I applied this modification (only C84&C87)

the wobble is less, (i had to recalibrate the touchscreen). It seems that the pen interrupt point is not 100% accurate, sometimes it comes from the other end of the screen, i think we need to find an RC combination.

aardvarq

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Re: Touchscreen wobble (cleanup of thread)
« Reply #2 on: February 01, 2011, 08:45:46 AM »
Tonight I put a 33 nF 0805 across C87 with noticeable improvement. 

The installation was a bit tight - using an 0805 cap on C87 doesn't leave enough room to put one comfortably across C84 so I left that unmodified.  Also, the capacitor was not fully flat on the board. Normally this wouldn't be an issue, but upon re-installation of the board, I found it to be tight against the plastic housing, with the extra piggy-backed cap pushing the board up .  So, I just wore the plastic down by a few thousandths of an inch using the flat of the screwdriver and everything was fine. 

Now,
1.  The screen is more sensitive making it easy to type and use in general.
2.  The shake still exists, but it's down by about 75% of what it was.  Now, it is only a minor annoyance instead of something that I was always fighting.

Many thanks to everyone who contributed to this.


Tablet:  Single Speaker - Utopia. Board matches the one which is pictured by Hardcore.

aardvarq

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Re: Touchscreen wobble (cleanup of thread)
« Reply #3 on: February 02, 2011, 06:25:50 AM »
Tonight I put a 33 nF 0805 across C87 with noticeable improvement... 


Sorry that I didn't get a photo, but for what it's worth, I've modified HC's first picture, showing what mine looked like with an 0805 paralleled against C87 (0603). On my board, a combination of off-center 0805 with the solder fillets made me shy away from doing C84. It's possible that it might fit on the other side of C84 (relative to the side that the piggyback is for C87), but then it gets close to the connector.

Destroyer

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Re: Touchscreen wobble (cleanup of thread)
« Reply #4 on: February 02, 2011, 11:52:49 PM »
Hi,
Yes C87 would make sense, because that is connected to pin 1 on the  Touch screen connector (pin 4 if you are looking at the back of the connector counting from the left as some people prefer to do)


Something we can try... ( ANYONE with a BROKEN (SMASHED) TOUCHSCREEN) , yes even with a broken touch screen you can still contribute.
Take the screen apart and match the layers of the touch screen with the edge connector.

It may be that this pin is connected to the Bottom plate, rather than the top plate of the touch screen.
This is important since it may mean if the DAS (Dumb Ass Suppliers) change the configuration of the touch screen  and the plates are reversed, that some people may need to connect the capacitor to a different point.


kelv

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Re: Touchscreen wobble (cleanup of thread)
« Reply #5 on: February 10, 2011, 07:27:58 PM »
Hi,
Yes C87 would make sense, because that is connected to pin 1 on the  Touch screen connector (pin 4 if you are looking at the back of the connector counting from the left as some people prefer to do)


Something we can try... ( ANYONE with a BROKEN (SMASHED) TOUCHSCREEN) , yes even with a broken touch screen you can still contribute.
Take the screen apart and match the layers of the touch screen with the edge connector.

It may be that this pin is connected to the Bottom plate, rather than the top plate of the touch screen.
This is important since it may mean if the DAS (Dumb Ass Suppliers) change the configuration of the touch screen  and the plates are reversed, that some people may need to connect the capacitor to a different point.



That might explain changing from one part number to another on the touch screens reduced my shake/accuracy issues..
mid run shortage perhaps? Think I threw my broken screen, But I hear Xaueious has one:)

leaplae

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Re: Touchscreen wobble (cleanup of thread)
« Reply #6 on: February 15, 2011, 07:57:02 AM »
Hey, Im new and know how to solder well and have steady hands (im 17), and want to do this mod on my A8. I broke my touchscreen approx 4hours after getting it, and sent it to www.ankaka.com where i brought it from, and 'apparently' its on its way back.
I only know a little about electronics - does the polarity matter on the cap? would this cap work? http://www.jaycar.com.au/productView.asp?ID=RC5380&keywords=10nf&form=KEYWORD. Thanks.

Destroyer

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Re: Touchscreen wobble (cleanup of thread)
« Reply #7 on: February 18, 2011, 04:32:02 AM »
Lol.....
Yep it might work but:

1. it is rated at 3kv (3,000 volts)
2. the leads are thick so soldering it  may damage the tracks of the pcb if it moves
3.  Polarity, it is essential that you use a 'non-polarized' component, that is to say there is NO polarity requirement,
Nothing will blow up, but the leakage across the plates of a polarized component may be too high to negate the electrical noise we are trying to remove.


These are  better:
Jaykar 47nf
Jaykar 33nf
Jaykar 10nf

But still a little large as regards the leverage the leads will apply to the solder joints, and if you must use a capacitor like this then ,epoxy it to the P.C.B first THEN solder the leads.

really you need to find some small SMT ceramics (no leads), or take the product to an electrical repair shop, with the info from the above article about C83,C84,C86,C87

HC

« Last Edit: February 18, 2011, 04:35:30 AM by Admin »

Naethegolfer

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Re: Touchscreen wobble (cleanup of thread)
« Reply #8 on: March 17, 2011, 09:42:08 PM »
Hi Guys,

It's been about a month since your last posts on this subject and I was wondering if things had moved on any.

I have been pouring over everyone's inputs regarding this tablet in the forums, and I must admit to you all, I am sitting looking at the insides of my tablet and my eyes are twinkling with anticipation of solder...

But before I get cracking on it, I took it apart to fix the broken touchscreen that I broke last month whilst taking it apart... ::)

So, Admin, I have a broken touchscreen. I've disected it (and not drawn blood for which I am happy. It's glass on the inside...) and here are the results;

Pin 1 leads to the Glass, Bottom part and runs Anti-clockwise round the screen
Pin 2 leads to the Plastic, Top part and runs Anti-clockwise round the screen
Pin 3 leads to the Glass, Bottom part and runs Clockwise round the screen
Pin 4 leads to the Plastic, Top part and runs Clockwise round the screen

Rotations are looking down on the tablet from above (mirror image of the photo).

Hope this helps and keep fighting the good fight!

Regards to all

Naethegolfer ;)

Destroyer

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Re: Touchscreen wobble (cleanup of thread)
« Reply #9 on: March 18, 2011, 12:39:24 PM »

This is great, but if you are interested in modding , checkout the blue tooth mod, which can be expanded to ANY USB device.

Some of the suppliers are starting to change the caps, others have been changing the LCD to cut down on the electrical interference and still others are continuing to sell the old crap to unsuspecting buyers.

I was in one of the local shops in ShenZhen and they are trying to clear this crap at 700-800 RMB, still had plenty of takers, mostly foreign , out on a shopping trip.
Buy a dodgy APad then skip over the road to get a really cheap  mobile phone clone, even apple devices are available.
Shame no one told these 'shoppers' that usually the RF sections are defective and as a result they are operating outside of the legal requirements for power.

Naethegolfer

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Re: Touchscreen wobble (cleanup of thread)
« Reply #10 on: March 18, 2011, 04:56:56 PM »
Hi admin,

I eventualy want to add an external USB camera to the pad (for in-car reversing) so the bluetooth mod may come in very useful. So...

Got myself a couple of capacitors...
Set up my soldering iron...
Started soldering...
folded the new capacitor out of the way ready to put the board back down on the housing...
Pulled out C87 completely along with part of the pcb...
... :o :-[ :'( ???...

I've decided to utilise a very thin wire on the right (remaining) bit of pcb and attach the capacitor to this. In hindsight, and for any other aspiring modders, this would have been the better way of carrying out the mod. I now need to find out where the other end can go. I've tried Pin1 on the other side, but this turned out to be mighty frustrating and kinda imposible.

Do you or anyone else have any ideas or suggestions? :D

Or know where to get another board if I've completely messed up this one  ;D

Destroyer

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Re: Touchscreen wobble (cleanup of thread)
« Reply #11 on: July 21, 2011, 01:00:34 AM »

BubbaHotep

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Re: Touchscreen wobble (cleanup of thread)
« Reply #12 on: September 02, 2011, 04:46:18 AM »
Do you still need/want a broken touchscreen that had "shake" issues?  I just broke mine and need to replace it.  If you want it I can send it to you if you want.

Destroyer

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Re: Touchscreen wobble (cleanup of thread)
« Reply #13 on: November 08, 2011, 04:10:24 AM »
Hi,
Sorry for the delay in posting, been really busy looking at Android and UAV's.
I'm fine for touch screens, don't really need it , but thanks for offering