As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER STARTING ENGINE AND HYDRAULIC SYSTEM, PRESSURE WAS UP AND NORMAL (1,500 PSI), THE BRAKES LOCKED UP AND AIRCRAFT WOULD NOT MOVE. FOUND THE POWER BRAKE VALVE RETURN FILTER BLOCKED. THESE FILTERS ARE CLEANED EVERY 24 MONTHS. NO HOUR REQUIREMENT. SUBMITTER STATES THESE FILTERS NEED TO BE CLEANED AT 400-HOUR INTERVALS.