Page 16 of your service manual states that PSPRT (Power Supply Protection) voltage must lie between 36-49V; outside of these, the protection shuts down.
Your line is low at 34V
The values given do not represent the voltage directly. For some reason Yamaha does not report the voltage errors directly.
It goes something like this:
The sum at the output of a resistor summing network is normally approximately zero volts.
Take the source voltage, usually 5 volts on the older ones, divide by 255.
multiply the error code by this remaining decimal value to see the actual voltage the microprocessor is reporting.
5V/ 255 = .0196078431
.0196078431 x let's say 45 = .88V
So the sum of the resistor network is approximately .9 volts HIGH, suggesting a negative voltage source may be LOW.