A B737-500 FLC FAILS TO ADHERE TO THE PROVISIONS OF THE LOUPE 9 DEP PROC AFTER A QUICK REVIEW ON THE GND AT SJC; CA.

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I DEPARTED THE SJC ARPT RWY 30L ON THE LOUPE 9 DEP; LINDEN TRANSITION. AFTER DEP; I TURNED R AND INTERCEPTED THE SJC 339 DEG RADIAL OUTBOUND. I WRONGLY ASSUMED THAT THE '120 DEG HDG/EXPECT VECTORS' WAS FOR A DIFFERENT TRANSITION OR DEP FIX AND DISREGARDED IT. AS WE STARTED TO INTERCEPT THE 339 DEG RADIAL; I REALIZED THAT IT DIDN'T LOOK RIGHT AND I ASKED THE FO TO QUESTION DEP CTL ON THE DEP PROC. CTL ADVISED US THAT WE HAD EXCEEDED THE 4 MI ARC AND TO TURN R AND REJOIN THE DEP. THE CONFLICT OCCURRED WHILE ATTEMPTING TO REJOIN THE DEP. CONTRIBUTING FACTOR; THE FLT DIRECTOR COMMAND BARS WERE NOT FUNCTIONING PROPERLY. THIS WAS AN ADDITIONAL DISTR. HOWEVER; THE ACTUAL CONFUSION WAS OVER THE PUBLISHED SID. THE FO AND I DISCUSSED THE SID AT THE GATE PRIOR TO DEP AND WE CONCLUDED THAT THE 120 DEG HDG WAS FOR A DIFFERENT TRANSITION. CORRECTIVE ACTION: IF THE '120 DEG HDG' AND THE 'EXPECT VECTORS' LINE CONTINUED TO TURN OR LOP BACK TO THE VOR; I THINK THIS WOULD CLARIFY THE DEP PROC. I ALSO SUGGEST THAT THE DEP CTLR COULD HAVE GIVEN US A HDG OR VECTOR ONCE WE QUESTIONED THE PROC AND WERE NO LONGER ON THE DEP.