Sometimes trying to fix something you make it worst. This is what have happened to a Lenovo A10 7600H tablet that i had. I was trying to repair the SMD soldered micro USB port and because i didn't had the proper tool i have used a 3000W heat gun and managed to short circuit the PCB and destroyed the contacts.
But if you don't succeed try try again and you should never be disappointed even if you finally could not fix what you are trying. Because even then, the lesson was learnt and next time you will surely do a better job.
So in my case i wasn't disappointed and try to figure out what i wanted to do.
- I did not want to have data connection but only charge the tablet.
- I didn't need the memory slots of the tablet.
So an idea came up! Can we use a universal battery charger for Li Ion batteries and bypass the internal circuits? And the answer is yes we can!
Step 1: Materials and Tools
The tools are practically the same for this kind of jobs
- Soldering iron with fine tip
- Soldering paste
- Wire cutter
- Wire stripper
- Small file
- Epoxy glue
- Duct tape
I had some thick cables from salvaging other old equipment and I bought only this universal charging PCB based on TC4056A IC
The reason for choosing this module is because it is very easy to change the maximum current from 1A to 0.5A and i wasn't sure if the module was getting very hot with 1A as it finally did. So i removed the solder from J1 jumper and the maximum current that the system provides is 0.5A without getting hot at all. Of course it will take double the time to charge the battery but this is something that it is not bothers me. I will charge it overnight.
Other implementations using TC4056A have an SMD resistor that can be changed to get various max limits currents. But my experience with SMD and the lack of the proper tool was the reason for this instructable so i didn't want to chase my tail using the same mistakes with SMD components.
Also this module is very small so i can put it somewhere inside the tablet without problem.
Step 2: Dissasemly and Connections
Opening the tablet wasn't an easy task if you don't want to damage it. So i did it very carefully. I previously watched a video about disassembling this tablet from here.
The battery is connected with many wires to the main PCB of the tablet with a 12 pin socket. At the side of the PCB all this 12 pins are exposed. Four of them are the positive connection (RED), the other four are the ground(GND) or negative connection (BLACK) and the other four are usually thermal and other type of sensors.
I have disconnected the battery and using solder paste i have soldered two thick cables to at least three of the connection of the positive (RED) and another three for ground (BLUE cable). The other ends of the cables where connected to the charging PCB to BAT (RED cable) and GND (BLUE cable)
The following step is very essential : With the multimeter in the short circuit testing position i have tested the connections between GND on the charging PCB and other ground connections on the tablet and the BAT connection with the connection of the 12 pin socket and making sure that i did not have any short circuit with NOTHING else.
Then i reconnected the battery and a charger. Using the multimeter in DC i have measured the voltage of the battery and it was starting to rise from 3.5V and the LED on the PCB board was red. Touching the PCB i found out that it was really hot. So i decided to remove the solder of J1 and have a maximum charging current of 0.5A. I left it to charge overnight and next morning the green LED was on. I measured the voltage of the battery and it was 4.19V. Success. I turned the tablet on and it was working as a charm.
Step 3: Final Arrangements
In order to fit the charging PCB, i have removed the memory slots PCB that was not used anyway and with a small file trimmed the plastic piece under the memory slots PCB.
I have positioned the charging PCB inside and put some epoxy glue to stick it.
I have made two small holes at the back cover of the tablet so the charging LEDs can be seen from outside and used some duct tape to close the memory slots opening leaving the charging micro usb uncovered.