My cellphone won't turn on and it has private data inside

[Sepehr]

Hi,
Last week my Nokia Lumia 520 was extremely low in charge (%3), therefore I plugged its charger. After a couple of hours, I reached my phone but it was turned off. I tried almost everything to turn it on, but nothing worked. I connected my cellphone to my computer with a USB cable and got the Windows' driver-not-found error.
Unfortunately, I used to store my personal data in the cell phone's internal (onboard) memory. Although I'm not worried about data loss, I don't feel comfortable to give the board to a repairman as I'll not observe what he would do with all the data inside it and they won't give any warranty for such things.
Are there any tricks to repair it by myself? Like by using a software on my PC to force the cell phone to boot via the USB or finding what has caused the problem?
Is it possible to erase the data before giving it to a repairman?

[Sepehr]

Take it physically apart and check out the battery and the contacts of the battery to the circuit board.
You do know that the back comes off of these phones and that there is a replaceable battery right behind the back cover, right?

The battery itself may be dead or the contacts may just be dirty or somehow bent.

Also with the proper technique and equipment it may be safely possible to charge the battery OUTSIDE of the phone and then when it is somewhat charged you could put it into the phone to see if the phone boots and works.

It should also be possible to buy or borrow a new battery and try it in the phone.

Actually if you know the right technique you might even be able to power the phone through the battery's contacts with a suitable 3.3VDC well regulated power supply.  The battery itself seems to be rated at 3.7VDC but you would not want to come close enough to that limit that you could accidentally go over it with a bad power supply.

I've had done that. The mainboard has many extra tiny SMD components which I guess may not be replaceable.
There are metal shields on every chip which look like they are soldered. I guess they are RF shields intended to minimize the radiation for decreasing SAR values, am I correct? You can see high-quality pictures at https://globaldirectparts.com/oem-nokia-lumia-520-motherboard-at-t/

How come there is no visible circuitry path on the board? is it sandwiched between the outer layers?

I don't have a multimeter yet but the battery seems to work as I connected an LED to it and it glowed.

One thing that I noticed earlier was that after powering the board, you can hear a very quiet low-pitched tone by bringing your ear next to one of the chips on the upper section of the board near the camera module.
Another thing which I noticed is that if I connect the board via a USB cable, there would be no voltage on the battery terminals of the board.

A friend recommended to check it with a power supply, mine (a cheapo adaptor) had only 4.5 volts so I did apply it to the battery terminals attached to the board after he said 4.5 volts would cause no harm. Nothing happened but now I'm a little doubtful if 4.5 volts would be harmful to the board's components or not.

[dicky96]

Actually if you know the right technique you might even be able to power the phone through the battery's contacts with a suitable 3.3VDC well regulated power supply.  The battery itself seems to be rated at 3.7VDC but you would not want to come close enough to that limit that you could accidentally go over it with a bad power supply.

A friend recommended to check it with a power supply, mine (a cheapo adaptor) had only 4.5 volts so I did apply it to the battery terminals attached to the board after he said 4.5 volts would cause no harm. Nothing happened but now I'm a little doubtful if 4.5 volts would be harmful to the board's components or not.

I'm not sure you either read or understood what the previous reply was telling you??

[Rasz]

its hammer time, brand new replacement is $40

[Sepehr]

Actually if you know the right technique you might even be able to power the phone through the battery's contacts with a suitable 3.3VDC well regulated power supply.  The battery itself seems to be rated at 3.7VDC but you would not want to come close enough to that limit that you could accidentally go over it with a bad power supply.

A friend recommended to check it with a power supply, mine (a cheapo adaptor) had only 4.5 volts so I did apply it to the battery terminals attached to the board after he said 4.5 volts would cause no harm. Nothing happened but now I'm a little doubtful if 4.5 volts would be harmful to the board's components or not.

I'm not sure you either read or understood what the previous reply was telling you??

I read that. Maybe I didn't exactly get what he said...
I did it before that post was published.

[CatalinaWOW]

You need a Widlarizer

[SaabFAN]

A workaround that worked for me a few times:
9V Battery connected directly to the terminals of a completely discharged Li-Ion Battery of a Sony Smartphone - Just for a few seconds, of course!!!
After this treatment, the phone turned on right away and also charged the battery. Before that, it didn't do ANYTHING. Even after 2 hours connected to the little power-brick there was no sign of life from it.

A few other times it also helped to just disconnect the battery for some time to allow any residual charge on the capacitors to dissipate. USB-Cable must be connected when Battery is reinserted btw.

[Cerebus]

You need a Widlarizer

A 4lb Widlarizer.

[WaveyDipole]

Is that better than a Batterizer?

[KL27x]

Last week my Nokia Lumia 520 was extremely low in charge (%3), therefore I plugged its charger. After a couple of hours, I reached my phone but it was turned off.

plus this

Another thing which I noticed is that if I connect the board via a USB cable, there would be no voltage on the battery terminals of the board.

plus this

One thing that I noticed earlier was that after powering the board, you can hear a very quiet low-pitched tone by bringing your ear next to one of the chips on the upper section of the board near the camera module.

= total wild guess that maybe one of the DC converters failed. Wherever you heard the "quiet low-pitched tone," maybe look around for an SMD inductor. Could be square with rounded corners, perhaps. Or a small disc shaped thing. Two leads on either side. Like a tiny short spool of ferrite with a coil of tiny wire in it. Or perhaps some squarish black boxy looking thing. Next to it you will find a bunch of tiny caps and a diode next to a small IC, perhaps.

Even if you find it and and test it to verify it is dead, and even if you could source a replacement, and even if you could do the microsurgery to replace it (or find a schematic and bypass it with lab power supplies), I bet the phone is still broke, though.

As for 4.5V (verified by a DMM) from this cheap power supply breaking the board, more? I doubt it caused any further harm. But anything is possible.  Powering it like that isn't the first nor last thing you ought to do. Nor anywhere in between. But it isn't that much overvoltage.

[KL27x]

If I were super desperate, I would power the phone with 5V from the USB jack and try to trace where this power rail goes (easier said than done on a multilayer board made with microscopic parts). And see where this trail ends. It should of course lead to a battery charger somewhere, and this should put some voltage out to the battery terminals. This is one of the known problems. There ought to be another voltage regulator that drops this to 3-some volts to power the phone.

[janekm]

Keep in mind that most modern phones won't power up without a working battery, even if 5V is supplied (to protect the file systems in case of sudden loss of power, I presume).
Unfortunately your phone is worth less than the battery (and certainly much less than the replacement main board, which is worth much less than the cost of trouble-shooting before a repair), so it's definitely "beyond economical repair".

Good news, you have the perfect justification for getting a new phone.

[Sepehr]

Keep in mind that most modern phones won't power up without a working battery, even if 5V is supplied (to protect the file systems in case of sudden loss of power, I presume).
Unfortunately your phone is worth less than the battery (and certainly much less than the replacement main board, which is worth much less than the cost of trouble-shooting before a repair), so it's definitely "beyond economical repair".

How does it distinguish between a real battery and a power supply?
I'll get my hands on my first multimeter soon and I'll try my best to solve the issue. I'd like to know what are the professional steps in troubleshooting it.

Good news, you have the perfect justification for getting a new phone.

Yeah!  Although I hope it will fix by its own.
But I have to research a lot before that. I hated Windows Phone, it was really a mess, at least in Lumia 520.

[amspire]

I must be missing something. The 520 battery is easy to replace and you can get them for well under $10 on ebay.

If the current battery has dropped below the minimum voltage allowed by its built in protection circuit, it switches off the battery which makes it hard to charge. Lithium batteries that have dropped to too low a voltage have a risk of catastrophic failure if recharged so this is protection. Just get a new battery.

It may be possible to replace the battery with a power supply, but it is also possible that if the phone cannot talk to the battery, it may refuse to boot. You have to know which terminals are the + and - terminals of the battery, and this may be hard to work out from the flat battery if the battery is disconnected from the terminals.

[Sepehr]

I must be missing something. The 520 battery is easy to replace and you can get them for well under $10 on ebay.

If the current battery has dropped below the minimum voltage allowed by its built in protection circuit, it switches off the battery which makes it hard to charge. Lithium batteries that have dropped to too low a voltage have a risk of catastrophic failure if recharged so this is protection. Just get a new battery.

It may be possible to replace the battery with a power supply, but it is also possible that if the phone cannot talk to the battery, it may refuse to boot. You have to know which terminals are the + and - terminals of the battery, and this may be hard to work out from the flat battery if the battery is disconnected from the terminals.

I know which ones are negative and positive termnials based on the back of the battery, but there's a third terminal which I don't know what it is, I've tried powering the board using only the negative and positive terminals and no connection to the third one which has a hollow circle symbol under it. Maybe that's why it won't boot?!

[janekm]

I must be missing something. The 520 battery is easy to replace and you can get them for well under $10 on ebay.

If the current battery has dropped below the minimum voltage allowed by its built in protection circuit, it switches off the battery which makes it hard to charge. Lithium batteries that have dropped to too low a voltage have a risk of catastrophic failure if recharged so this is protection. Just get a new battery.

It may be possible to replace the battery with a power supply, but it is also possible that if the phone cannot talk to the battery, it may refuse to boot. You have to know which terminals are the + and - terminals of the battery, and this may be hard to work out from the flat battery if the battery is disconnected from the terminals.

I know which ones are negative and positive termnials based on the back of the battery, but there's a third terminal which I don't know what it is, I've tried powering the board using only the negative and positive terminals and no connection to the third one which has a hollow circle symbol under it. Maybe that's why it won't boot?!

That's right, the third terminal is either just a temperature sensor (in which case it can be simulated with a resistor of appropriate value) or it can be a one-wire interface to a battery management IC inside the battery pack.

[Sepehr]

I'm wondering how do they repair the board other than using spare parts from other boards? Is it repairable at all? or did the manufacturer ever intend to design it in a way to make repairs possible?
There are no visible traces of the circuitry path on the PCB and all the connections are either too tiny or hidden underneath the components. 

[janekm]

I'm wondering how do they repair the board other than using spare parts from other boards? Is it repairable at all? or did the manufacturer ever intend to design it in a way to make repairs possible?
There are no visible traces of the circuitry path on the PCB and all the connections are either too tiny or hidden underneath the components. 

Yes, typically spare parts from other (donor) boards are used. I've got an iPhone 6 donor board on my desk (bought out of curiosity), the RAM, SIM holder, and what looks like two of the power management ICs had been salvaged before I bought it. More popular phones have (reverse-engineered, most likely) repair manuals available, and some quite impressive rework is possible:

Actual CPU replacement:


Or there's this rather entertaining video on an iPhone 6S built entirely from spare parts: