This is my son's helicopter toy that didn’t want to start charging. In this Instructable, we will look at the steps I took to investigate the fault and how I managed to fix it.
Soldering Iron: http://s.click.aliexpress.com/e/bZIcQlUk
Solder Wire: http://s.click.aliexpress.com/e/bFYJxK4g
Precision Screwdriver set: http://s.click.aliexpress.com/e/uYch5NI
Super Glue: http://s.click.aliexpress.com/e/cZfgI0E8
Step 1: Disassemble and Test the Battery
To start investigating what the fault was, I first grabbed the smallest screwdriver I have and removed the 4 screws that were holding the two halves of the toy together. What I had in mind at the time was that somehow the battery was over-discharged so I focused my investigation toward it. The battery is a small Lithium cell with a nominal voltage of 3.7 volts. When discharged the cell voltage needs to be close to 3 volts so when plugged in, the charge controller chip can start the charging process.
So, I measured the voltage across the battery terminals and it showed close to 3.1 volts which should have been enough for the charge chip to work with and this got me confused. My expectation was that this will be way under 3 volts but since it wasn’t I changed the investigation path to the charger.
Step 2: Test the Charger
I tried to measure the voltage coming out it and at first, I was not getting the full voltage on the connector pins. I then tried to measure on the connector directly but since the inside hole is too small I wasn’t really able to do it. Instead, I decided to break open the charger as well.
Inside the charger, there was a small chip, and at first, I thought that it might have some role in the charging process. After looking at the PCB, I realized that this chip was not used for the charging process but instead, was used for the control of the helicopter toy. When the button on the charger is pressed, it sends a signal through the infrared LED and it turns on the motor.
I tried to measure the voltage that was across the terminals coming out of the PCB and again for some reason this was not the full voltage. Going backwards I didn't have the full voltage until I reach the battery terminals and for some strange reason, the full voltage was then applied to the entire length of the charger all the way to the connector. I guess the problem was that I was not getting a good connection on the meter leads that somehow prevented me from seeing the entire voltage.
Step 3: Try to Charge the Battery
Having diagnosed the charger as being OK I once again focused my investigation to the battery and decided to try to trickle charge it to a higher voltage so the chip can start charging it. I first desoldered one of the connections on the battery and on my bench power supply, I set the voltage to 3.6 volts and connected it to the battery using crocodile clips. When connecting the battery this way you need to be very careful as this might cause the battery to catch fire. Always make sure that you have a metal tray that you can place the battery inside in case this happens.
After a while, I measured the voltage on the battery again and it started slowly climbing. At all times I monitored the battery temperature as this process forces energy to it without any control or monitoring as with the usual charging process. Several times I disconnected the charger and soldered the battery to the board to try it out but unfortunately, this did not help. Something else was going on that I was not able to understand.
At this moment I had the toy opened up on my bench for a few days and I spent some more time on it thinkering without filming until I finally had a breakthrough.
Step 4: Don't Forget to Check the Basic Stuff First
The switch that is used to turn on the toy also doubles up as a breaker on the battery charging circuit when operating. It has two sets of pins where two of them are connected while turned on, providing the power to the control circuit and the motor and the other two are connected when the toy is turned off, making a connection between the charging port and the battery.
However, one of these connections had a cracked solder joint that I very easily fixed with my soldering iron. Once fixed, the charging indicator LED started glowing indicating that the toy is now fixed and we can continue playing with it.
Step 5: Fix Any Mechanical Damage and Assemble
Before assembly, I used some super glue to fix the cracks on the outer shell and assembled everything back together.
Step 6: Enjoy Flying
All in all, this was a fun exploration. Being falsely sure of what the problem is from the beginning, I failed to look for an easy fix and got obsessed with the battery voltage being too low. However, the time spent on this repair is well worth it as I now know a lot more about how the toy operates and how those bipolar switches are used in controlling two separate circuits.
If you too managed to learn something, I would encourage you to subscribe to my YouTube channel, leave any question or suggestion down in the comments and until the next one, thanks for reading.