I'm trying to convert an E14 RGB LED bulb to be able to power it from a lithium battery. Inside the bulb are 2 PCBs - a transformer and a LED driver - which are connected by 3 wires. Black and red are DC ground and positive, white is for something else.
When I apply DC voltage to the driver board it works only while I'm touching the white wire with a finger. I tried to connect this wire to positive or to ground directly and via a capacitor - nothing seems to work.
On the transformer PCB this white wire is connected to one of the mains terminals via a 1 μF capacitor. On the driver board it is connected to ground via a 6.8 nF capacitor.
Maybe somebody here knows what this third wire is for, and what circuitry could possibly replace my finger?