Changing the battery in your Syma S107G helicopter is probably the most common repair job you will do. The standard battery is a lithium polymer (li-po) 3.7v 150mAh which is soldered in place. I usually upgrade this to 180mAh which gives a longer flying time. It is possible to fit a 240mAh battery but the weight penalty outweighs any advantage of the higher power as the motors need to use more power to get it off the ground!
There are different ideas about ways of changing the battery. You can cut the wires then rejoin them to the wires on the new battery. This adds unnecessary weight. You can unsolder the wires from the battery itself and then solder them to the new battery but this can be very dangerous if solder runs between the terminals and shorts out the battery. In extreme cases it can catch fire so I would not attempt it. The proper way is detailed here. It may appear complicated but in practice can easily be done in 20 minutes to half an hour.
Start by removing the 2 canopy screws, 1 each side.
Carefully remove the canopy by sliding it forward, taking care not to dislodge the wires which go to the LED in the nose of the helicopter. This reveals the battery, shown here.
Carefully remove the battery from its mounting together with the self adhesive pad. On some versions of the S107G it is possible to unsolder and replace the battery at this point but great care is needed. On the pictured R5 PCB the battery is soldered to the underside of the board so further dismantling is necessary which I find easier in most cases anyway.
Remove the highlighted screw on each side of the helicopter and remove the 2 tail stays.
On the right hand side of the helicopter when viewed from the rear, undo the 4 highlighted screws then remove the metal side plate.
Remove the 2 white spacers from the main frame and store safely.
On the left side of the helicopter undo and remove the 2 highlighted screws to release the main frame from the landing skid.
Carefully separate the metal frame from the landing skid. It is then usually possible to unsolder and replace the battery but on this example the battery is soldered to the underside of the board so it is also necessary to remove the 2 screws which secure the PCB to the landing skid.
The solder connections can now all be clearly accessed with the red and black battery wires connected to the outermost 2 positions on the PCB. The battery can now be unsoldered ready for the replacement to be fitted.
Using a fine tipped soldering iron, unsolder the two battery connections from the PCB and solder the wires from the replacement battery to the board, making sure the polarity is correct. I have found that the safest way is to connect the negative black wire first to the terminal next to the charging port. Then connect the positive red wire to the terminal next to the on/off switch. On this example I have connected the battery to the terminals on the top of the PCB instead of underneath. This photo also shows the PCB wiring connections which are, from top to bottom:
1. Negative battery connection
2. Blue wire from M2 (front) motor.
3. Black wire from M1 (rear) motor.
4. Red wire from tail motor.
5. Blue wire from tail motor.
6. Red and white wires from M1 and M2 main motors
7. Positive battery connection.
Switch on the PCB to test that the LED’s in the nose and on the circuit board illuminate.
Assembly of the helicopter is basically the reverse of the disassembly sequence. When rejoining the main frame to the landing skid, take care to ensure that the inner rotor shaft seats correctly in the little bush which protrudes through the PCB and does not make contact with other components which can cause damage.
Finally, when seating the battery it is a good idea to fix a thin trip of adhesive tape to each side of the battery to hold it in place in its mounting cradle.
I hope you have found this guide useful and if you have any questions or comments please use the Contact page to send a message.
Syma S107G helicopter repair blog 