MECHANIC IS INFORMED THE B757-200 ACFT HE PREVIOUSLY WORKED; WOULD NOT PRESSURIZE AND REQUIRED AN AIR TURNBACK. A FORWARD LEFT HAND NOSE WHEEL WELL BULKHEAD PANEL WAS NOT FULLY SECURED.

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I WAS INFORMED BY MGMNT THAT ACFT X HAD AN AIR TURN-BACK IN JULY BECAUSE IT WAS UNABLE TO PRESSURIZE. I CAME IN ON EARLY CALL AND WAS TOLD TO CHANGE OUT THE NOSE GEAR STEERING VALVE THAT HAD ALREADY BEEN STARTED. THE COVER (PANEL) OVER THE NOSE GEAR STEERING VALVE AHD BEEN PARTIALLY REMOVED WHEN I TOOK OVER THE JOB. I FINISHED REMOVING THE COVER (PANEL) AND FOUND THAT THE TOWING BYPASS LEVER WAS STICKING. MYSELF AND ANOTHER AMT REPLACED THE SEALS ON THE BYPASS LEVER AND OPS CHK LEAK CHK OK. I REINSTALLED THE COVER (PANEL) OVER THE NOSE GEAR STEERING VALVE AND SIGNED OFF THE OPEN ITEMS ON THE WRITE-UP. I MISUNDERSTOOD THAT THE NOSE GEAR STEERING VALVE COVER (PANEL) THAT I FOUND PARTIALLY REMOVED AND REINSTALLED WAS THE ONE THAT WAS WRITTEN UP ON THE WRITE-UP. THE ACTUAL PANEL THAT WAS PARTIALLY REMOVED IS IN THE FORWARD L-HAND SIDE OF THE NOSEWHEEL WELL. THERE WAS NO MAINT MANUAL REF PAPERWORK TO SHOW A LOCATION OF THIS PANEL. NOT THINKING THAT A PANEL SO FAR AWAY FROM THE PROB WITH THE STEERING VALVE WAS PARTIALLY REMOVED I SIGNED OFF THE NOSE GEAR STEERING VALVE COVER (PANEL) THINKING THAT THIS WAS THE PANEL WRITTEN ON THE WRITE-UP. WHEN PANELS ARE PARTIALLY REMOVED THERE SHOULD BE A MAINT MANUAL PICTURE SHOWING THE LOCATION OF WHAT PANELS ARE REMOVED OR PARTIALLY REMOVED. THIS WILL AVOID CONFUSION WHEN SIGNING OFF THE WORK. I WILL PAY MORE ATTN TO THE ITEMS THAT ARE WRITTEN UP ON WRITE-UPS AND WILL LOOK UP IN THE MAINT MANUAL AND ITEMS IN QUESTION TO AVOID CONFUSION IN THE FUTURE. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: REPORTER STATED HE WAS CALLED IN ON EARLY OVERTIME. THEIR NORMAL SHIFT HAD NOT STARTED; SO HE DID NOT HAVE A LEAD. THE TURNOVER GIVEN TO THE ON-SHIFT SUPERVISOR AND THEN RELAYED TO HIM SEEMS TO BE WHERE THE MISUNDERSTANDING ABOUT A PARTIALLY REMOVED PANEL ON THEIR MAINT WRITE-UP BEGAN. REPORTER STATED THEIR LEADS USUALLY ENTER THE MAINT AND SIGNOFF DATA IN THEIR MAINT ACFT HISTORY AND LOGBOOK. HE BELIEVES IF ONE OF THE LEADS WAS ON DUTY; THEY MAY HAVE CAUGHT THE DISCREPANCY IN THE SIGNOFF OF THE MAINT WRITE-UP.