NEXUS 7 slow charging problem solved?
Last week, I found that my nexus 7 (16g wifi only) start to charge really slow or even not charging. This happen after I upgrade my tablet to android 4.4.2(no root, no mod). I tried all the ways I could found on internet such as disconnect the battery and reconnect after few minutes, downgrade to android 4.3 or 4.2, changing to different type of charger and so on but failed.
After tried for few days, I was frustrated and decided to throw away the tablet. But 2 days ago, when I tried to charge the tablet with samsung galaxy tab2 7.0 charger, I manage to charge from 0% to 50% in two hour. I thought my tablet was back to alive but the tablet stop charging after 50% battery. I tried with oem 2A charger or cheapo china ipad charger and the charging starts but slow and sometimes not charging. I search online and found out that the samsung tab2 7.0 charger has 1.2V at both data pins and both data pins was shorted. I checked my asus oem charger and found out that both data pin was shorted but no voltage supplied.
I take a usb cable, strip and cut both data wire and short both data wire at micro usb side. I connect the tablet to the samsung charger and the tablet start charging and charge at normal speed to 100%. I thought that was the solution but yesterday, when I tried to charge the tablet which has 10% battery remains with samsung charger and my modified usb cable, the tablet charge, but in slow rate. I take half a day to charge to 50%. i exchange the moded usb cable with a normal usb cable and this time the tablet charge to around 80% in one hour. I was confused. Does my tablet need voltage of 1.2V at both data pins for the tablet to recognize as normal charger?
I start to do my experiment by using the oem charger. I apply around 1.2V by using resistors connect to the +5v and gnd. My tablet start to charge at normal rate that i can get the increment in battery % after 1 or 2 minutes in screen off mode. After charge to around 25% my tablet stop charging. I checked the data pins voltage and found out to be around 1.8V. 1.8V??? not 1.2V??? I check the resistors connection and disconnect my tablet from the usb cable. The data pins is now 1.2V. I connect my tablet back to the usb cable, wait for the tablet to start charging at normal rate and disconnect the data wires from the resistor. I tested with multimeter and found out that there was a voltage of 3.1V at data pins (shorted together) from the tablet when charging.
After a few tries by changing the resistors with different values to increase or decrease the data pins voltage, I manage to get a combinations that works well with my charger and my tablet charge normally. With the resistor combination, I get a voltage of 0.5V when no tablet connected and around 1.2V when tablet connected and start charging by using a resistor of 1Kohm connect from the +5V pin to the data pin and 100ohm connect from the data pin to the ground. Actually my tablet shows sign of normal charging when I apply 1V to 1.5V to the data pins that I choose 1.2V for full charging testing. I manage to charge my tablet from 0% to around 30% by using the samsung charger, 30% to 60% using the cheap ipad charger and 60% to 100% using the oem charger. No sign of stop charging or slow charging during the charging process. Maybe this is the solution to the charging problem?
I hope that someone which is more professional in this fields will try my way and give me the final results of the most suitable resistor combination or is my way of solution, or is this just an coincidence or my solution can only be applied onto my tablet? Warning: Try at your own risk.