Author Topic: EEVBLOG #135 Kindle Resets  (Read 17622 times)

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Offline FreeThinker

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EEVBLOG #135 Kindle Resets
« on: December 22, 2010, 05:29:29 pm »
Hi Dave
Being reading that the leather case has caused other problems as well as the resets, they are ( allegedly ) causing cracks in the kindle case.http://www.crunchgear.com/2009/07/15/the-official-kindle-2-case-is-cracking-the-kindle-2-thats-a-problem/ .This nice little money spinner is turning into a bit of a nightmare!!
In your vblog you tested the lighted version which does not have the problems of the no lit one are you sure they are mechanically the same apart from the black paint?Tried to find detailed pics but not turned up any so far, seems very strange that one causes problems and not the other even though your tests pointed to the connectors being well protected.Maybe we'll see a few turning up on ebay cheap now ( I think they are too expensive at the moment £50 is more take off price point in my view).
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Offline mikeselectricstuff

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Re: EEVBLOG #135 Kindle Resets
« Reply #1 on: December 22, 2010, 05:52:56 pm »
Dave - there is a scenario that I didn't see you test - enable the output first, then short the terminals. I only noticed you test enabling while shorted.
It is likely that any enable will have some level of  soft-start, limiting the worst-case surge current, however if the output is already enabled, shorting will produce a potentially very high di/dt, which could be enough to gitch the power sufficiently to cause a reset.

I have seen some reports that the bad cases had a single piece of metal instead of 2 seperrate clips.

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Offline Ferroto

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Re: EEVBLOG #135 Kindle Resets
« Reply #2 on: December 22, 2010, 07:23:42 pm »
Since the non-led version is painted, you should simulate an intermittent connection. If there is a current control device it may not be able to compensate with the rapidly changing demand and that could cause a brownout.

You could use a mosfet to switch the current on\off and use a frequency generator to drive the mosfet at different frequencies.
 

Offline FreeThinker

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Re: EEVBLOG #135 Kindle Resets
« Reply #3 on: December 22, 2010, 07:39:31 pm »
Since the non-led version is painted, you should simulate an intermittent connection. If there is a current control device it may not be able to compensate with the rapidly changing demand and that could cause a brownout.

You could use a mosfet to switch the current on\off and use a frequency generator to drive the mosfet at different frequencies.
Good point.Also the top pin is sprung and any movement could cause the bottom contact to bounce causing noise etc.
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Online EEVblog

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Re: EEVBLOG #135 Kindle Resets
« Reply #4 on: December 23, 2010, 02:06:14 am »
Dave - there is a scenario that I didn't see you test - enable the output first, then short the terminals. I only noticed you test enabling while shorted.
It is likely that any enable will have some level of  soft-start, limiting the worst-case surge current, however if the output is already enabled, shorting will produce a potentially very high di/dt, which could be enough to gitch the power sufficiently to cause a reset.

I have seen some reports that the bad cases had a single piece of metal instead of 2 seperrate clips.

That's the first time I've heard of solid metal connecting the two. I've only heard reports that they have been measured (properly) as being completely open.

In any case, I HAVE MADE MY KINDLE RESET! after some more playing.
Haven't pinned down the exact cause/sequence yet but I'm working on it.
It may turn out to be a combination of the metal tabs after all, well see.
Murphy of course ensured this happened AFTER I posted my video!

Dave.
 

Offline Jimmy

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Re: EEVBLOG #135 Kindle Resets
« Reply #5 on: December 23, 2010, 06:49:03 am »
Could it be that the paint is conductive and little flakes of conductive paint are causing havic inside.
 

Offline Psi

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Re: EEVBLOG #135 Kindle Resets
« Reply #6 on: December 23, 2010, 07:38:42 am »
Maybe its contact generated noise on the RX pin that's causing it, an intermittent contact shorting RX to GND causing a character, or string of characters, to be read by the uart.

That character or string might instruct the device to reset. Could be a buffer overflowing somewhere because of unexpected characters or even be the official serial reset code if the reset string is simple or very short. Hell, it could even be a feature designed to stop people trying to reverse engineer the serial protocol by triggering a reset on unusual serial data.

Would explain why its only an issue on the case version with the black paint on the contacts. A solid short on the version with the brass contacts wouldn't cause this issue, only one where the paint was half worn off and there was an intermittent/scratchy short.
« Last Edit: December 23, 2010, 07:49:59 am by Psi »
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Re: EEVBLOG #135 Kindle Resets
« Reply #7 on: December 23, 2010, 08:42:49 am »
Damn, I can't seem to reproduce the lockup!
Did it consistently 4-5 times today but now it's all rock solid.
Thought I be able to reproduce it consistently and come up with a sequence that made it happen, but now it's not playing ball  >:(

Dave.
 

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Re: EEVBLOG #135 Kindle Resets
« Reply #8 on: December 23, 2010, 08:43:56 am »
Dave - there is a scenario that I didn't see you test - enable the output first, then short the terminals. I only noticed you test enabling while shorted.
It is likely that any enable will have some level of  soft-start, limiting the worst-case surge current, however if the output is already enabled, shorting will produce a potentially very high di/dt, which could be enough to gitch the power sufficiently to cause a reset.

Tried that many times now, that ain't it.

Dave.
 

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Re: EEVBLOG #135 Kindle Resets
« Reply #9 on: December 23, 2010, 08:45:56 am »
Could it be that the paint is conductive and little flakes of conductive paint are causing havic inside.

Almost certainly not. The reports say it always goes away when not in the case, consistently.
And goes away when tape is put on the bottom of the tab.
Flakes (even if they were conductive) would be too inconsistent to explain all the reports.

Dave.
 

Offline mikeselectricstuff

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Re: EEVBLOG #135 Kindle Resets
« Reply #10 on: December 23, 2010, 11:21:38 am »
Might be interesting to look at the magnitude of any transient voltage dip under short conditions repeatedly, e.g. with a cycling relay- could be that it's a coincidence of a voltage dip and a hardware/software state when either it's drawing more current, or more susceptible.
Bear in mind that when just sitting there doing nothing, the  kindle's CPU is going to be asleep for most of the time, so maybe it only happens when there's a short while the CPU happens to be awake.

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Offline TheDirty

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Re: EEVBLOG #135 Kindle Resets
« Reply #11 on: December 23, 2010, 01:46:32 pm »
I have the no LED case with the black mounting tabs.  If you want me to check anything on it, let me know.  Otherwise, like you said, they look exactly the same except my mounting tabs are black.  I thought they were hard plastic until I saw this.

EDIT:  I should add that I never had this issue, but I use the case only sporadically.
« Last Edit: December 23, 2010, 01:54:31 pm by TheDirty »
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Offline JohnS_AZ

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Re: EEVBLOG #135 Kindle Resets
« Reply #12 on: December 23, 2010, 03:30:42 pm »
I have to wonder if this isn't some sort of ESD event.

Leather is almost at the top (positive end) of the triboelectric series. If a user is reading their Kindle and develops a large charge on the cover (sliding it across countertop, or clothing), and then closes the cover there could be a significant field induced charge developed inside the Kindle. The difference between the LED and Non-LED covers might be the fact that the lit models have a connection to the system ground that might serve to discharge (albeit slowly) any charges that develop on the cover.

Dave, you need to add an electrostatic field meter, and an electrostatic voltmeter to your collection of test gear. 8-)

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Offline JohnS_AZ

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Re: EEVBLOG #135 Kindle Resets
« Reply #13 on: December 23, 2010, 04:30:32 pm »
Thinking further, there is a fairly simple (crude) test that you could do:

- Lay the cover down open on an insulating surface
- Turn the Kindle on and set it in position on the cover but do not attach the clips
- Vigorously rub the inside of the left side of the cover with something from the bottom of the triboelectric series ( ie. silicone, teflon, vinyl, polypropylene / ethylene / urethane, ),
- With a pencil or some other other insulator quickly flip the cover closed.
- See if the Kindle is still running

This would be a very crude test. If there is no effect, it could still be an ESD issue. If there -IS- a repeatable effect, odds are you've ( I've  :) )  nailed it.

 
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Offline Derek R

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Re: EEVBLOG #135 Kindle Resets
« Reply #14 on: December 23, 2010, 04:38:13 pm »
I have said the following in several places already:  :)

1)  I have a problem Kindle/case combo but "seem" to have fixed it with a 2.2 Mohm resistor and a 0.1 uF capacitor in parallel, wired across the cover terminals.   It has been working for almost a week now without a hiccup.   Nothing magic about the values, I just wanted to absorb ESD charge with a "reasonable" time-constant.
2)  I am seriously wondering if people are attacking the problem the wrong way by repainting the terminals or putting tape over them.   Perhaps what we should be doing is removing the paint so that the tabs can make intimate contact with the Kindle internals, ie keep them at the same potential as the system and prevent ESD.   This may be why the problem does not seem to happen with the lighted cover...

I'm sitting here waiting for a replacement lighted cover to be delivered any moment.  Amazon doesn't want me to return my current one, so I may try a little paint stripper on the terminals - although I'm concerned about removing all residual corrosive stripper before plugging it into the Kindle.
 

Offline Derek R

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Re: EEVBLOG #135 Kindle Resets
« Reply #15 on: December 23, 2010, 04:44:24 pm »
@JohnS_AZ
I have been able to make the Kindle reboot by rubbing polar-fleece and touching the Kindle cover or itself close to the lower terminal...
Not every time, perhaps 40% of the time.
Derek
 

Offline JohnS_AZ

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Re: EEVBLOG #135 Kindle Resets
« Reply #16 on: December 23, 2010, 04:46:16 pm »
I'd try to remove the paint/coating mechanically, with something like a small wire wheel on a Dremel tool.

This issue is a little frustrating for me: I have a complete suite of high-end ESD test equipment, but I don't have a Kindle or a cover. Anyone near Phoenix want to loan me one?  :)
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Offline mikeselectricstuff

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Re: EEVBLOG #135 Kindle Resets
« Reply #17 on: December 23, 2010, 06:26:48 pm »
What could be happenning is the paint is initially acting as an  insulator, but then  breaking down once a  certain level  of charge has built up on the metal clip,   discharging to the contact.
If this is the case,  then  removing the paint may fix the  problem.

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Offline Derek R

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Re: EEVBLOG #135 Kindle Resets
« Reply #18 on: December 23, 2010, 06:49:53 pm »
mike -
That's my thinking also, and perhaps those people who have reported success by repainting or adding tape are simply increasing the dielectric strength (without actually solving the real underlying problem).
 

Offline Derek R

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Re: EEVBLOG #135 Kindle Resets
« Reply #19 on: December 23, 2010, 07:14:20 pm »
I've taken the plunge and used a Dremel tool to remove the paint.  I couldn't of course get underneath the tabs, but will try some fine sandpaper.    Everything is fine so far (after 1 minute  :D)
Only time will tell...

Update:   I am recording 4v between the terminals, so I'm obviously making connections.   Everything is still working (3 hours later) after many attempts to crash it.
« Last Edit: December 23, 2010, 09:36:55 pm by Derek R »
 

Offline Henrik

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Re: EEVBLOG #135 Kindle Resets
« Reply #20 on: December 24, 2010, 01:25:08 pm »
My Kindle 3 has failed to wake up several times, requiring a full reboot, but hasn't had any reset problems.  Anyway, after I applied tape around the metal tabs on my non-lighted cover I haven't had any wake up problems at all.  I sure hope it stays that way.

I hope you keep us updated on your paint removal solution, Derek R.
 

Offline Derek R

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Re: EEVBLOG #135 Kindle Resets
« Reply #21 on: December 24, 2010, 05:34:53 pm »
Henrik -
 I have been trying to make it crash for 24 hours now.   I've tried to induce static charge by rubbing with all sorts of cloth etc (which used to make it crash).   So far it has been rock solid...
   Of course, we all know that Murphy is lurking just around the corner  ;D

Update (12/26):   Still going strong, I've now read 2-1/2 books without a single problem.
« Last Edit: December 26, 2010, 01:54:05 pm by Derek R »
 

Offline Henrik

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Re: EEVBLOG #135 Kindle Resets
« Reply #22 on: December 28, 2010, 08:13:36 am »
Update (12/26):   Still going strong, I've now read 2-1/2 books without a single problem.

That's great! Mine is still going strong as well, no problems at all.

In other news: I called Amazon about refunding the cover.  They gave me $60 to buy a lighted cover, and I don't have to return the old one.  In addition I got $21 for shipping and handling since I live outside the US.  That's quite a bonus :)
« Last Edit: December 28, 2010, 08:15:25 am by Henrik »
 

Offline Derek R

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Re: EEVBLOG #135 Kindle Resets
« Reply #23 on: December 28, 2010, 01:11:10 pm »
Henrik -
That's great news.   Absolutely no problems here either!

Unfortunately my experiment will come to an end today - I am traveling to New Zealand for a couple of weeks and will take the replacement lighted cover with me.

I hope we have nailed this one!
 

Offline mechanoid

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Re: EEVBLOG #135 Kindle Resets
« Reply #24 on: January 22, 2011, 07:24:53 pm »
Hi all. I'm new to this site but I thought that I might add my thoughts on this problem.

First, problems attributed to the Kindle cover have only ever been reported on the non-light versions.  These differ in that they have painted metal tangs. I have two Kindles. One has frozen once in many months use, and has rebooted twice when the cover was opened. The other newer one either freezes or reboots almost every day.  The paint on both appears fully intact, which would appear to rule out short circuits as a probable cause anyway.

I have seen the Kindle in the act of rebooting after the cover has been opened, but not turned on.  My girlfriend has seen this a number of times, mainly after she has walked downstairs carrying the closed Kindle tucked under her arm.  Here's what I think happens.

1. The non-conducting closed face of the cover rubs on the non-conducting surface of the screen and the Kindle body. The tribo-electric effect transfers a static charge from one surface to the other.
2. When the cover is opened, the charged surfaces are separated. Being non-conductive surfaces these charges take a long time to dissipate.
3. The circuit board is effectively one big conductor. The static charge on the screen surface attracts charge from the conducting board, effectively raising its potential above 'ground'
4. However, there are two lumps of conductor not effectively connected to the circuit board, namely the two painted metal clips. There now exists a potential difference between the conductive clips and the board.
5. If the potential is high enough, then the paint breaks down, and charge flows rapidly to equalise the potential difference. This puts a nice big spike into the power rail (or the other connections that Dave identified on the lower connector). This resets the device, or freezes it, or damages it, or who knows what !

People have apparently eliminated the problem by either increasing the isolation using tape, or removing the paint from the contacting areas to connect them fully. And of course, taking it out of the case altogether.

Actually it occurs to me that bringing the power rails of a piece of complex digital electronics out to a couple of external metal contacts is not exactly the best piece of design in the world. For this reason I don't think either solution is that great, since it is possible to put a static discharge straight into the device at any time by just touching these metal clips. After all, you wouldn't go poking your fingers onto the circuit board of your PC without proper anti-static precautions, now would you ! Incidentally, if you go putting discharge spikes into pins that control things to do with current, what will that do to battery discharge ?

The trouble with static effects, as I'm sure a lot of you know, is that they can be difficult to reproduce. You're more likely to see this if the air is very dry (it has been here recently) and you carry the book so as to rub the cover on the screen just before you open it. This seems to be the major difference between the way I and my girlfriend use our Kindles.  However, I'm not going to rubbing the cat against the screen just to see if it (the Kindle) resets.  My inclination is just to cut off the tags and stick the Kindle to the case with Velcro. Or get a refund and buy a different case.

Of course, electronic equipment for sale in the EEC must be tested for compliance with the appropriate standards for electro-magnetic and electrostatic susceptability. I'm sure the Kindle was - its got a CE mark. But was it ever tested with the case attached, I wonder ?  Anybody with access to the appropriate test facilities care to try this ?
 


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