im not that extremely expierienced with electronics.
I Bought a sonic reducer and fried it with a too hot soldering iron.
Now i found the scematics here But the only thing icant find any informations is the blue circle with white center an zwo of the bridge cables.
The black lines are jumper wires ("bridge cables") , and the white circle indicates that there is a connection between the two bridge cables at that spot.
If you were building from that layout, you would need to use two jumpers, solder them both in at one end (the top connection for the upper cable, and the lower connection for the lower cable), then you would need to solder the two ends TOGETHER at the white spot.