domenica 21 ottobre 2012

Nokia N900: broken USB, fixing charging

I had to abandon my first Nokia N900 because of broken USB port. The microUSB receptacle of the N900 is directly soldered on its mainboard (yes, the most stressed part of the phone without any safety: brain-damaged engineering is not an Apple exclusive).

When it broke, I bought a second N900, saving the first one for backup purposes. And after one year of careful usage, on a Friday late evening it suffered the same fate, meaning that:
I won't ever buy Nokia products again.

Sala operatoria: pronti per l'intervento sul Nokia N900
MicroUSB port is required both for data connection and for battery-charging. Without the microUSB port, you need to power off the phone, take out the battery and charge it on some external charger, which is quite annoying.

After a bit of googling I decided to put a header in place of the microUSB-receptacle but it was even harder than imagined. The five "pins" of the receptacle are some tiny 0.5mm-spaced drops. I eventually was able to solder D+ and D- cables (photo below), which are needed to use "tethering", that is: charging the phone while you use it as a modem. But -sigh!- a few minutes later I crashed them without hope to restore (they were not meant to resolder). This means I have to forget about tethering.

La monetina da 0,10€ serve per far capire quanto erano "grandi" e "vicine" le saldature da fare
Then I decided to short them; shorting D+ and D- (or, at least, 220 Ohm resistance) is required by the N900 to accept any 5V source to charge the battery. Fortunately, GND and +5V are replicated on the "test pads"; GND is also the center pin of the battery connector.

Applying +5V to the 5V/GND pads will regularly charge the BL-5J battery because D+ and D- are always shorted.

Opening the N900 was quite easy: four small screws for the screen and two small Torx for the keyboard and keyboard cover. More on that on forum.

Recuperati 5V e GND e "shortati" D+ e D-
I am now able to charge the N900 without having to power off / extract battery. After a bit of dremeling, I steadily placed the ugly 4-pin female header (chosen because "safe for my pockets); it does not perfectly fit, and my N900 does not "close" well, but at least I don't have to switch to another phone (moving calendars, addressbook, music, videos, etc and learning apps, configurations and so on).

I also switched screen and keyboard (both a bit scratched) with the ones from my first N900, so that my current unit feels somewhat rejuvenated...

L'orrendo header femmina serve a non far pasticci quando l'N900 è in tasca

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