For my own particular reasons, I want to solder my own headers on a PCA9685 board.
One difference between a factory complete board and a board where the user has to solder on DuPont header pins is what looks like a can capacitor. The capacitor is on the factory complete boards but it is missing on the "kit" boards.
I want to control 9g servos. Is the missing capacitor relevant? Are there other differences?
I've never used that board but it looks like it's just a decoupling capacitor.
It's used to store charge from the battery and provide a more stable voltage to the servos when they're activated. This helps avoid over stressing the battery and also helps prevent any power dips from being passed back into the rest of the circuitry.
Try using a 100uF electrolytic. If you have trouble with weak or very jerky servo response you may need to increase to a larger (than 100uF) value.
I've used the Adafruit 16 channel PWM Servo Driver - PCA9685 board to run a Hexapod. It used 12 micro servers without the cap. Adafruit has great documentation, they even address your question.
Adding a Capacitor to the thru-hole capacitor slot
We have a spot on the PCB for soldering in an electrolytic capacitor. Based on your usage, you may or may not need a capacitor. If you are driving a lot of servos from a power supply that dips a lot when the servos move, n * 100uF where n is the number of servos is a good place to start - eg 470uF or more for 5 servos. Since its so dependent on servo current draw, the torque on each motor, and what power supply, there is no "one magic capacitor value" we can suggest which is why we don't include a capacitor in the kit.
Thanks. Good information.
I use the servos to move track switches on my model railroad. I set up the code so only switch moves at a time.
Therefor, I doubt I need the capacitor.