I would also check that there is not an issue with one of the relays/LPFs. Without power connected to the PA (brown power wire), check each band for continuity from the antenna jack to TP7. You should have a connection for all of the bands.
The above reasoning is that all of the relays are de-energized for 10 meters (28 MHz). Not sure why all of the other bands have low output, however it is worth a try.
Just a thought.