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I've noticed a few others with seemingly the same symptoms. The tablet is operating normally for a few weeks and then after a routine recharge you notice the battery has gone flat, 2% or 1% only. It powers up fine once plugged in (boots up as if it had been turned off), and reports that it is charging - complete with red LED - but the battery never seems to get any of the juice.

My reseller was very helpful in coordinating a warranty exchange with the vendor, even arranging an advanced exchange so I could get my replacement sooner. The replacement worked beautifully - for 10 days, until it happened again.

Instead of demanding another replacement, I'm waiting for my 1st tablet to get back to the vendor so they can have a look at it - we'd both like to avoid any more transactions. I'm hoping they can diagnose what the problem is and offer a fix.

Meantime, I'd like to try to figure it out. Maybe if we can isolate the cause we can help others avoid this. Here are my thoughts...

Firmware - probably not the cause, I was running C8lean v0.51 on the first tablet and Asure's CM7 on the 2nd. Besides, there are a ton of people using these ROMs. I tried running the Battery Calibrator app, nothing.

Power Surge - Perhaps, but the tablets were plugged into different outlets (with power bars) at the time of their failure. Same room though, but other electronics have been fine.

AC Adapter - my main suspect, although the vendor doesn't think so. Both tablets were charging on the same adapter (from the first tablet) when they failed. The adapter that came with the second tablet is made by a different company, with a slightly lower voltage output. Here they are:
Communication Device Telephony Battery charger Gadget Adapter
The smaller one on the left is the suspect, it puts out 9.47v and the English lettering says the model number HW222SSLL. The adapter that came with the replacement tablet puts out 9.26v, and the model is JK180902000C (mostly Chinese writing).

Internal charging circuit failure - unlikely, what are the odds of getting two tabs with a faulty circuit? My reseller asked the vendor to test the charging of the tablet before shipping, apparently it went through a couple cycles without issue. Does anything look unusual about the battery info?
Font Screenshot Software Technology Display device


I haven't opened the tablet up yet to have a look inside, don't want to jeopardize another warranty claim if it comes to that, although I'm very curious. I'd be interested in hearing from others with this issue, or hardware gurus with any thoughts.

Thanks...
 

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Discussion Starter · #2 ·
I just remembered something -

The warning is there for a purpose. IIRC you should not discharge Li-Ion batteries to zero because they may get into a state when they cannot be rechnarged using normal equipment anymore. So when it starts to pop up the warning, it's good idea to connect a charger or turn off the tablet. Maybe it's OK to lower the warning to, say, 5%, but not disable it completely.
Could I have left the battery too long before putting it on a charge? You know, with the phone.apk working the battery while it's 'off' it might have drained it past a threshold, no?

I was reading about ways to kick start a zero'd li-ion cell, I'm tempted to put the tablet in the freezer for a few days!
 

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Hi

First, now I feel that this is a major problem with this device since Ive been reading about so many people facing this problem.

Once I got this problem, I decided to get into the root of the problem to try and repair it myself since sending it back to my vendor would cost me almost the same as the cost of a new one.

1. I checked the voltage at the terminal where the battery is soldered. It reads 3V. Our battery is 7.4 volts so there is no way our device could operate.
2. I disconnected the battery and still the tablet could run through direct power from the adaptor so the tab is running on direct source 9V power
3. I checked the voltage of the disconnected battery. It read 5.6V. This is higher than the voltage being read when the battery was connected to the motherboard. This made me think that the battery is actuall not the source of the problem.
4. To confirm this, I tried charging the battery directly from the charging adaptor. It got charged to 7.4V. Connected this to the tab and now it ran fine. Interestingly, once I connected the charger to the tab again, the battery started discharging very rapidly as the voltage at the baterry terminal on the PCB dropped to 3V.

Conclusion: There is a bad IC on the motherboard which is causing the voltage drop at the battery terminal on the motherboard. This does not allow the battery to get charged. The tablet is up and running when plugged in because the architecture of the motherboard splits the power to the battery and as a direct power to the tab when plugged in.

I am now trying to identify the messed up IC on the board. Probably has got to do with the Voltage step down converter located near the power button. Its code on my tab is MP1482DS. Its in point shows 9V but all other pins are dead.

Also on the backside there is a probe point for 5V. That is also dead.

I am not an electronic engineer and its difficult for me to identify the problem further. Moreover, there are no reliable repair guys here.
I suggest you guys try the same and maybe one of us will be able to identify what exactly needs to be done.

By the way, this happened after I tried installing softwares to root the tab. Dont know if this would have any direct impact.

Regards

Surya
 

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Hi

I was actually referring to the one marked out in Yellow. Its the voltage convertor. I tested it using a multimeter. The input is coming at 9V but all other pins are ground. I suspect it to be the culprit. However, the one you pointed out is also directly linked with the battery. Ill test it tonight and post whatever I can gather.

I am trying to source these 2 ICs. Will replace them once I get those but it seems they are not common in India so might take sometime. Meanwhile try to push your vendor. Im sure he can help us in a better way. Unfortunately my vendor is not that supportive


P.S. Even if you plug in the the charger in the wrong way, it wont cause any damage because it has an AC to DC convertor. Unless that guy opened the charger and then changed the polarity.

Regards
 

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What I meant was that to change polarity you need to break open the charger and interchange the wire connections. I doubt even that guy would have done that.
And I didn't play with my charger and have the same problem. The charger is giving me 9 volts which is fine. I've arranged the 2 ic from china.will reach in about 15 days.
I tried checking that battery controller ic marked in red. Its giving me 3 v. Same as what I'm getting at the battery terminal. Looks like this could be faulty. But the part number on mine is different from what you said although its too fine to be read with a naked eye.
 

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Discussion Starter · #8 ·
What I meant was that to change polarity you need to break open the charger and interchange the wire connections. I doubt even that guy would have done that.
And I didn't play with my charger and have the same problem. The charger is giving me 9 volts which is fine. I've arranged the 2 ic from china.will reach in about 15 days.
I tried checking that battery controller ic marked in red. Its giving me 3 v. Same as what I'm getting at the battery terminal. Looks like this could be faulty. But the part number on mine is different from what you said although its too fine to be read with a naked eye.
I'm trying to find clues as to the cause of this - what voltage is your charger precisely? Does it look like either of the two in my original post?

Would a difference of 200mv (between my two chargers) even be enough to cause a problem?
 

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What I meant was that to change polarity you need to break open the charger and interchange the wire connections. I doubt even that guy would have done that.
And I didn't play with my charger and have the same problem. The charger is giving me 9 volts which is fine. I've arranged the 2 ic from china.will reach in about 15 days.
I tried checking that battery controller ic marked in red. Its giving me 3 v. Same as what I'm getting at the battery terminal. Looks like this could be faulty. But the part number on mine is different from what you said although its too fine to be read with a naked eye.
@surya: would you please tell what you order, and from where? I think I have same problem with these IC and looking for these

EDIT: my engineer friend suggest BQ2057 - same linear charger as EUP8057, but easier to find (Texas Instruments)
 

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@surya: would you please tell what you order, and from where? I think I have same problem with these IC and looking for these

EDIT: my engineer friend suggest BQ2057 - same linear charger as EUP8057, but easier to find (Texas Instruments)
My condolences, @Lubo...do you have any clues as to what might have caused the failure (3rd party adapter, power surge, overheat, electromagnetic pulse, solar flare...)?

Those ICs look very similar in function - same pinouts too.

EDIT: I wonder if some volatge isn't getting to the IC to 'turn it on' to start charging...would the function block diagram in the attached PDF help detect if the chip is getting what it needs to activate?
 

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The same situation, the tablet is no longer charged. Shows a charge of 5-7% and all.
 

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In my case i broke the power adapter's tip. Then i look and found same size tip (2.35 x 0.75 mm)
and then, when i connected tip to power wires, i reversed polarity (stupid mistake)

now my tablet is working, but when connected to power it becomes VERY hot in minutes,
but battery still charges, works for 1-2 hours and quick discharges.

I ordered this IC
http://bg.farnell.com/texas-instruments/bq2057wtsg4/ic-charge-management-2057-tssop8/dp/1214427?Ntt=BQ2057

Next week, when i got it will try to replace
 

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And I sent back MID to merimobiles, they have excellent support and 1 year warranty!
 

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I'm trying to find clues as to the cause of this - what voltage is your charger precisely? Does it look like either of the two in my original post?

Would a difference of 200mv (between my two chargers) even be enough to cause a problem?
Hi

Yes my adaptor is similar to yours and no 200mV wont cause an problem. Ive noticed that on my other Dropad A8, one that is working fine so far, there is leakage of current on the outer body and I had felt the same on the previous tab also. This could also be a reason for IC's to get burnt.
 

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@surya: would you please tell what you order, and from where? I think I have same problem with these IC and looking for these

EDIT: my engineer friend suggest BQ2057 - same linear charger as EUP8057, but easier to find (Texas Instruments)
Ive been trying to get these from China. Only problem being my linear charger is not EUP8057 and its too fine to be read with a naked eye. Once Im able to read it, Ill try buying that as well.
 

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Discussion Starter · #16 ·
Hi

Yes my adaptor is similar to yours and no 200mV wont cause an problem. Ive noticed that on my other Dropad A8, one that is working fine so far, there is leakage of current on the outer body and I had felt the same on the previous tab also. This could also be a reason for IC's to get burnt.
Could you elaborate on what you felt, and were you able to confirm a leakage with measurements?

Does this mean that there would be a short somewhere inside the device?
 

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Could you elaborate on what you felt, and were you able to confirm a leakage with measurements?

Does this mean that there would be a short somewhere inside the device?
It is absolutely true - voltage leakage!
when I was in Paris, my wife played angry birds, tablet was powered, and i touch my wife !!!
i feel for sure 50 Hz vibration !!!

maybe not grounded power outlet there in Paris?!
At my home never such feeling
 

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ouch if lowering the charging voltage does help then i don't know what to think...

did they just use the protection pcb for disconecting the charger? like battery empty, connected to charger and voltage drop to lower than 7,4V, if battery is full protection pcb cuts of because of more than 4,28V on every cell thus led goes green ?
( theres just two wires that means no balance here ? )
 
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