As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
RETURN TO BLOCKS. FLT NR 8690 PDX TO MFR. ACFT TAXIED TO RUNWAY RUN UP AREA. WITH ENGINE RUNS COMPLETED, ATTEMPTS TO CONTACT CLEARANCE DELIVERY FOUND NO VOICE BEING TRANSMITTED FROM EITHER NR 1 OR NR 2 RADIOS. ACFT WAS TAXIED BACK SAFELY TO BLOCKS FOR MX. R&R THE PILOTS PUSH TO TALK SWITCH.