10-03-2012, 04:40 AM | #1 |
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K3 battery voltage? (I²C details)
I took apart my unresponsive K3 the other day, and measured the battery voltage. To my surprise there was a grand total of 0V between the '+' and '-' terminals!
There was also 2.8V between either of these and either of the SDA/SDC terminals. I'm not a stranger to I²C, and there are typically pull-up resistors on both the data and clock lines, so maybe that shouldn't be so shocking. So, here are my questions:
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10-03-2012, 07:29 AM | #2 | |
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No, that is not normal - the battery terminals are battery terminals. The full charge on the K3 battery brings it up to nearly 4.2v. The SoC will detect a low voltage condition, slow to appox. 1/10 the normal clock speed and run at 2.8 - - - Intended I suppose to run "just enough" to control the charger. It is very likely that battery is dead now from over-discharge. It is also very likely that the battery management in the Kindle will not be able to recover the battery from that discharge level, although an external Li-Ion charger might be able to do it. If the K3 is still under warranty - send it home. That is where mine is headed. |
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10-03-2012, 08:35 AM | #3 |
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I left it plugged in over night, and this morning I measured 3.7V over the battery terminals, which I gather is a Good Sign™.
It booted once or twice, and even let me choose a book once, but then it hung. When plugged in to a PC it once showed up as a Kindle and once as "MX 35 / SE Blank RINGO", which I believe is a fall-back mode of the SoC. I'll leave it plugged in for another couple of days, but it may well be that the battery is dead. If so, where can one find a trusted replacement battery? I see a bunch of them on eBay, but I'm a bit weary of buying lithium batteries from unknown sellers, as there's no way of knowing how (and how long) they've been shelved. |
10-03-2012, 08:39 AM | #4 |
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Try for at least 4.1v (90% +)
But you may well be correct - the 'failure mode' is lowered storage capacity. I.E: you may now have a 1.8mAh battery rather than a 1,800mAh battery. |
10-03-2012, 10:09 AM | #5 |
Carpe diem, c'est la vie.
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I just bought 80 K3 demos. I could sell you one with a broken screen super cheap so you could swap batteries. They even have 3G so you could debrick it and swap screens instead if you want to...
Last edited by geekmaster; 10-03-2012 at 10:23 AM. |
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10-03-2012, 10:36 AM | #6 | |
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Just in case I can't sweet talk Amazon into exchanging mine. |
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10-03-2012, 10:44 AM | #7 | |
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(Admittedly I'm in deepest Europe (Switzerland) so shipping might be exorbitant.) |
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10-03-2012, 10:48 AM | #8 | |
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Last edited by geekmaster; 10-11-2012 at 09:12 AM. |
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10-03-2012, 11:03 AM | #9 | |
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And if you have to ship it inside a kindle, why not make it worthwhile? How much would you want for a 3G with broken screen? (I believe that it would be possible to swap screens from my old device? If these are demo-units, is it still possible to de-brick them and register with Amazon?) |
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10-03-2012, 11:07 AM | #10 | |
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10-11-2012, 04:24 AM | #11 |
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I tried again to see if I could revive it. I charged the battery (using a bench power supply, set to 4.1V, current-limited at 150mA) for about an hour last night. (I would have left it longer, but at the same time I didn't want to leave it over night.) It looked like the battery retained some charge, as the terminal voltage rose from 3.6V to 3.74V. However, this morning it was down to 3.55V (I left the battery in the kinde.)
My guess is that there's some short-circuit somewhere that drains the battery faster than the internal charging-circuitry can charge it. I have had a look at the accessible parts of the PCB, but I can't find any tin-whiskers, dust-motes or anything like that. I might try to flush it clean with compressed air and-or PCB cleaner, to see if that dislodges something. But if that fails I think I've got a broken PCB on my hands. At the same time, I'm less and less inclined to spend much more time on it, as my Paperwhite should arrive in a couple of weeks. |
10-11-2012, 05:32 AM | #12 |
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Hm, put a current meter in between battery and Kindle, just to see if it isn't the battery's internals that are de-charging? A counter-check for the theory that it's the Kindle draining it? But I do well understand that you're losing interest in the device when there's a KPW being shipped to you :-) Good luck in getting some money back on ebay for the trusty, old but unfortunately a bit broken K3. The display is fine, so it's still worth a bit.
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10-11-2012, 05:38 AM | #13 | |
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What Ill do next, instead, is to remove the battery and attach my power supply directly to the kindle. That way I can see (on my fancy power supply) how much current it's taking. Can someone clarify that only the +/- terminals of the battery are used? I tried to connect a 'scope to the SDA/SDC terminals, but I never saw anything move. |
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10-11-2012, 08:03 AM | #14 |
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I know very little. but have seen pictures of a 3 recharge. + and - were all I saw used.
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10-11-2012, 08:35 AM | #15 |
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I just played a bit more.
I connected my external power supply to the battery terminals (instead of the battery). The power supply is set to 4.1V (I've got some rather thin wires and I worry about the voltage drop. But measuring at the terminals it never dips below 3.9V.) While the unit is 'idle' I measure a current draw of ~120mA. If I slide the power switch for 15 seconds the current draw drops to 0 until I release the switch, when it goes back to 120mA. Sometimes¹ the current draw starts to fluctuate wildly between 80mA and 220mA. Sometimes the green LED starts flashing very slowly. (Five seconds on, five seconds off.) During this entire procedure the screen didn't flicker a single pixel. Unfortunately I don't have a PC close, so I can't say what it does on the USB. ¹I must admit that I'm not quite sure what caused this. I wasn't able to reproduce either phenomenon. |
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battery, i2c, voltage |
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