K8055 analog output maximum level

I recently bought a K8055 and managed to control it by using the dll with the mingw compiler. Everything works as expected but for some reason the maximum analog output is something like 4,71V instead of the 5V which it should give according to the specs.
Because I am currently testing my software, no load is attached to the output ports yet, the values were measured using a multimeter directly on the the screw terminal. The USB port is supplying something like 5.1V, so this cannot be the problem I think. Do I need to adjust something to get a 5V output on the analog out ports?

Any help is greatly appreciated!

The LEDs LD9 and LD10 load slightly the PWM outputs of the PIC microcontroller.
By removing the resistors R18 and R19 you’ll get slightly higher output voltages from the analog outputs.