What was found
PDX FLIGHT NR 2419, AFTER PUSHBACK, DURING NR 3 ISO VALVE TEST, OBSERVED INTERMITTENT NR 3 HYD CAUTION LIGHT PRESS FLUCTUATION ON NR 3 HYD SYSTEM +- 1800-2600 PSI. AIRCRAFT RETURNED TO GATE. MAINTENANCE, WHILE TROUBLE SHOOTING, FOUND SYSTEM 3 AND DCMP BOOT STRAP ACCUMULATORS LOW. SERVICED BOTH ACCUMULATORS IAW SERVICING PLACARDS. ALSO, BLED SYSTEM 3 HYD SYSTEM IAW AMM 29-10-00-870-005. OPS CHECK GOOD IAW AMM 29-12-01-710-801. NO PARTS REPLACED. AIRCRAFT RETURNED TO SERVICE.