There should not be any negative voltage anywhere. So, you may not be measuring what you think you’re measuring. And in any case, there is not a DC voltage that can be measured there; it’s an oscillating signal that you can view with an oscilloscope, but the “DC voltage” that you measure will depend upon several factors including the type of meter that you use.
All of the red LEDs are connected to the LED10 line. So, check that line carefully, both at resistor R10 on the main (blue) circuit board, and its connections on the red ring. Make sure that it’s not accidentally connected (electrically) to something that it shouldn’t be, and that there is actually a connection from R10 to the ring.
