The silk screening on the rev 2.0 PCB for D4 is wrong. D4's cathode (striped end) connects to the Base of Q3. For that to happen the diode must be installed upside down to what is shown on the PCB's silk screening.
I don't know what the difference is between a rev. 2.0 and a rev 2.1 PCB so I don't know if this error has been corrected. To test it use your multi-meter to check for continuity between the lower eyelet for D4 and the center eyelet of Q3. If you have continuity between these two solder pads install the diode accordingly (striped end [cathode] to Base of Q3).