B737-300 CREW LWOC; AFTER THE STABILIZER TRIM FAILED IN THE NOSE DOWN DIRECTION.

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EVERYTHING NORMAL UP TO THIS POINT. AT 1200 FT AGL; I CALLED FOR FLAPS 30 DEGS. NOSE DOWN MAIN ELECTRIC TRIM FAILED. NOSE UP AVAILABLE. USED MANUAL TRIM TO ADJUST PITCH. CONTINUED TO LNDG. LNDG WAS A SAFER DECISION INSTEAD OF GOING AROUND AND DEALING WITH NUMEROUS FLAP/PITCH CHANGES WITH ONLY MANUAL TRIMMING NOSE DOWN AVAILABLE. AIRPLANE WAS STABLE. DURING THIS TIME; I REMEMBER HEARING FROM APCH 'CLRED FOR THE VISUAL RWY 16L.' I DO NOT REMEMBER HEARING INSTRUCTIONS TO SWITCH TO TWR. I DID RESPOND AT THE 1000 FT CALL 'CLRED TO LAND.' I FAILED TO FOLLOW MY TECHNIQUE OF VERIFYING I HEARD CLRED TO LAND BECAUSE I WAS VERY FOCUSED ON 'FLYING THE AIRPLANE.' STILL NO EXCUSE; BUT TRUTHFUL REASON. AFTER LNDG; FO SAID HE TRIED TO CONTACT GND AND WAS ON CORRECT FREQ; NO ANSWER. RAMP TOLD US TO CALL DEN GND CTL. DEN GND GAVE A PHONE NUMBER. I CALLED; REALIZED WE MIGHT NOT HAVE RECEIVED 'CLRED TO LAND.' I DID EXPLAIN I WAS DEALING WITH A FLT CTL PROB. DURING TAXI IN; I WAS TESTING MAIN ELECTRIC TRIM AT EACH FLAP SETTING; NOSE UP AND NOSE DOWN ON THE LOWER R SIDE OF THE PEDESTAL WHERE THE TKOF WARNING HORN IS INSTALLED. WROTE UP MAIN ELECTRIC TRIM. MAINT TOOK PLANE OTS.