What was found
SELECTED LANDING GEAR HANDLE DOWN AT 170KTS, 2300FT, DESCENDING ON THE 16R GLIDE SLOPE AT SLC, & NOTHING HAPPENED. NO AIR NOISE, NO LANDING GEAR DOOR INDICATION, RECEIVED 3 RED UNLK LIGHTS ON THE LANDING GEAR INDICATOR. PERFORMED A DISCONTINUED APPROACH, WITHOUT TOUCHING THE LANDING GEAR HANDLE, THE LANDING GEAR CAME DOWN AND INDICATED 3 GREEN ON ALL PANELS. R & R MLG HANDLE IAW AMM 32-31-11-04, LANDING GEAR NORMAL CONTROL MICROSWITCH UNIT (2GA). REMOVAL & INSTALLATION. OPS CHECKED GOOD. ACCOMPLISHED OP CHECK OF THE PROXIMITY DETECTION SYSTEM IAW AMM REF 32-00-00-05 GENERAL. ADJUSTMENT & TEST. ALL OPS CHKD GOOD. ACFT OK FOR CONTINUED SERVICE.