Hello,
What I did next was the following:
I connected the RX line to the red side of my voltage meter.
The black side I connected to the ground.
Here I found a voltage of around 7V (7,3-7,4).
By playing several notes at the same time this amount gets less.
The more notes I play at the same time, the lower this amount becomes.
Is this of any help in our quest?
Thanks!!!!!