ACR SMT WRONG DME FREQ MADE PREMATURE DESCENT.

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THE F/O WAS FLYING. I WAS THE NON FLYING PLT AND THEREFORE; REVIEWED THE APCH PLATE AND MONITORED PROGRESS. CONDITIONS DURING THE RPTR PHASE WERE IN VFR CONDITIONS; OCCASIONAL IFR. THE CHICAGO HEIGHTS NAVAID WAS SELECTED PRIOR TO THE OCCURRENCE. BOTH NAVAIDS AND DME RECEIVERS WERE SET TO CGT. ATC ISSUED A VECTOR FOR ILS 31L AT MOW. THE NAV RECEIVERS (VOR) WERE SET TO THE ILS 31L FREQ AND FORTIFIED. THE DME RECEIVERS WERE NOT RECEIVING THE 31L SIGNAL WELL ENOUGH FOR NAV; SO BOTH WERE RESET TO CGT NAVAID. WHILE TRACKING THE ILS 31L FRONT COURSE; STEP DOWN PROCS ARE ILLUSTRATED ON THE PROFILE VIEW IN LIEU OF THE G/S. BOTH G/S WERE MONITORED. #1 INDICATED OFF AND A FLAG WAS IN VIEW. #2 INDICATED G/S UP AND A PARTIAL FLAG. AT THE INDICATION OF 13.7 DME; THE G/S INFO APPEARED UNRELIABLE; SO A DSCNT TO 4000 FROM 5000 WAS INDICATED. DURING THE DSCNT; CROSS CHK WAS COMPLETED WITH G/S INFO 'NOT VALID.' WE HAD BOTH DECIDED THE INDICATIONS WERE STUCK IN THE UP OR OFF POS. AT THE 4000' DME FIX; FURTHER DSCNT WAS INITIATED TO 3000'; WHEN IT WAS REALIZED BY A FURTHER CROSS CHK AND IDENT OF ALL NAV AND RECEIVERS; THE DME RECEIVERS; SEPARATE RECEIVERS; NOT SIMILAR TO ANY OF THE NEWER ACFT RADIO SET UPS. THE DME RECEIVERS WERE BOTH SET TO THE WRONG NAVAIDS. WE INITIATED A CLB BACK TO THE APCH PLATE ALT; 5000'; AND ADVISED ATC. ATC ADVISED NO PROB; TO STAY AT OUR CURRENT ALT; 3800'; THEN DSNDED US TO 3000'. G/S INFO WAS CORRECT WHEN WE ARRIVED AT PROPER DSCNT LOCATION. DME ON ILS 31L FREQ. MANY YEARS AGO; I READ OF A HVT WHICH HIT A MTN TOP WHILE ON APCH TO AN ARPT IN ALASKA. SOME OF THE NAVAIDS RECEIVERS WERE SELECTED INCORRECTLY. THEY DID WHAT I DID. I COULD NOT IMAGINE SUCH A STUPID THING EVER HAPPENING TO ME. IT DID!! THERE WEREN'T ANY MOUNTAINS TO RUIN OUR DAY; THANK THE LORD. AND I THOUGHT I WAS CAUTIOUS AND COMPETENT. RECHK; RECHK; RECHK.