ACR MLG DEVIATED FROM CLRNC ROUTE DUE TO ACFT NAV RADIO PROBLEM.

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FLT FROM ATL TO MSP. PER STANDARD FLT PLAN CLRED VIA JUDAS 6 ARR TO MSP. APPROX 70 DME NW OF BADGER VOR ON J70 ZAU (133.32) CALLED TO ASK IF WE SHOWED ON J70. WE ANSWERED AFFIRMATIVE. ZAU REPLIED THAT WE SHOWED ON RADAR TO BE 10 MI S OF J70 AND GAVE US A RIGHT CORRECTION TO INTERCEPT J70. WHEN THIS HAPPENED; I (CAPT) WAS FLYING WITH MY NAV RADIO TUNED TO THE BADGER VOR WITH J70 OUTBND ARWY SET IN MY OBS WITH THE COPLT'S NAV RADIO TUNED TO THE GOPHER VOR AND THE PROPER INBND J70 ARWY RADIAL SET IN HIS OBS FOR THE INTERCEPT. AFTER ZAU TOLD US OF THIS ARWY DEVIATION; BOTH PLTS VERIFIED THE CAPT'S NAV RADIO FREQ AND IDENT. WE BOTH VERIFIED THE PROPER RADIAL SET ON THE CAPT'S OBS. ALL CHKED OUT OK. NEXT WE TUNED THE COPLT'S NAV RADIO TO THAT OF THE CAPT'S AND OBSERVED A NEARLY FULL-SCALE DEFLECTION OF COPLT'S VOR NEEDLE TO THE RIGHT OF SCALE; VERIFYING THE OFFSET WHICH ZAU HAD OBSERVED ON RADAR. WE WERE CHANGED TO MSP CENTER FOR 133.75. WE TOLD MSP OF THE SUSPECTED DISCREPANCY BTWN #1 AND #2 NAV RADIOS; ASKED FOR ANOTHER LOCATION FIX WHICH MSP SHOWED TO STILL BE S OF CENTERLINE BUT CORRECTING; AND TOLD CENTER WE WOULD ENTER THESE DISCREPANCIES IN ACFT LOGBOOK FOR MAINT TO CHK IN MSP. COPLT'S NAV RADIO WAS USED FOR REMAINDER OF ARR SEQUENCE; EVEN THOUGH THE CAPT'S VOR NOW INDICATED CORRECTLY WHEN TUNED TO BOTH GOPHER AND MINNEAPOLIS VOR'S. ANOTHER CAPT VOR DISCREPANCY WAS NOTED WHEN INTERCEPTING THE MSP LOC 29-1 FINAL APCH COURSE. MSP MAINT WAS NOTIFIED VIA RADIO AND CAPT ENTERED A SHORT VERSION OF THE ABOVE NARRATIVE ON ACFT LOGBOOK PAGE CAPT DESCRIBED PROB TO TECH. DIAGNOSIS: INTERMITTENT ERRONEOUS READINGS/INDICATIONS ON #1 VOR NAV RECEIVER. FIX: R & E MECH INSTALLED NEW NAV RECEIVER (#1) WHICH CHKED OK. ACFT THEN DEPARTED FOR BISMARCK.