2 B757-200 ACFT WERE DISPATCHED WITH UNMODIFIED THRUST MGMNT COMPUTERS CAUSED BY INSPECTION OVERSIGHT.

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ON MAY/XA/98 AND MAY/XB/98 I HAD TO VERIFY THAT ACR ACFT XYZ AND ZXY HAD A MODIFIED THRUST MGMNT COMPUTER INSTALLED. I HAD TO CHK THE DATA PLATES ON THE UNITS AND INSTALL NEW COMPUTERS IF THE PART NUMBERS ON THEM WEREN'T CORRECT. I BELIEVED THE ACFT WERE IN COMPLIANCE WITH MY INSPECTION AND SIGNED THE LOGBOOKS TO REFLECT THIS AND THAT NO COMPUTER REPLACEMENT WAS REQUIRED. DURING A COMPANY SPONSORED FOLLOW-UP INSPECTION; IT WAS DETERMINED THAT BOTH OF THESE THRUST MGMNT COMPUTERS WERE UNMODIFIED AND NEEDED TO BE REPLACED ACCORDING TO THEIR PART NUMBERS. THESE UNMODIFIED PART NUMBERS WERE YYZZXX-G2. THE MODIFIED PART NUMBERS ARE YYZZXX-G3 AND YYZZYX-G2; WHICH ARE VERY SIMILAR TO THE OLD NUMBER. I MUST HAVE BEEN CONFUSED ON THE NIGHTS IN QUESTION AND MISINTERPED THE BAD NUMBER FOR A GOOD ONE. I HAD PERFORMED THIS INSPECTION MANY TIMES PRIOR TO THESE INCIDENTS WITHOUT COMPLICATION. I BELIEVE THESE INCIDENTS OCCURRED BECAUSE I WAS COMFORTABLE WITH THE PROC AND PERHAPS A LITTLE COMPLACENT. FURTHERMORE; I WORK SHIFT XA00-XI00 AND HAVE TROUBLE STAYING FOCUSED ALL THE TIME.