B737-300 CREW HAD TRACK DEV AFTER BEING DISTRACTED BY ACFT PROBS IN ZOA CLASS A.

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RTE DEV. WE HAD AN UNSCHEDULED ACFT CHANGE IN SMF. ASSIGNED ACFT WAS STILL BEING WORKED ON BY MAINT WHEN WE ARRIVED. THE 'A' SYS ENG DRIVEN HYD PUMP AND A LNDG GEAR 'UP' WERE REPLACED. FINALLY PUSHED OFF THE GATE 1 HR LATE. AFTER TKOF; I CALLED FOR 'GEAR UP;' BOTH 'A' SYS LIGHTS CAME ON AND I SAW 'A' SYS PRESSURE DROP TO ZERO. A FEW SECONDS LATER; BOTH LIGHTS WERE OUT; PRESSURE RETURNED TO NORMAL AND THE GEAR FULLY RETRACTED. I ENGAGED THE AUTOPLT AND SELECTED VOR/LOC TO JOIN THE 090 DEG RADIAL FROM A 120 DEG HDG. WE DISCUSSED THE SIT AND DECIDED TO CONTINUE; FEELING THAT IT WAS A TEMPORARY CONDITION CAUSED BY AIR IN THE HYD SYS DUE TO THE MAINT ACTIVITIES. WE TOOK OUT THE QRH TO ASSESS PROCS IN CASE OF FURTHER 'A' SYS PROBS. DUE TO PREOCCUPATION WITH THE PROB; I FORGOT TO ENGAGE THE LNAV AND THE FO FORGOT TO CHANGE HIS VOR TO THE FRIANT RADIAL FOR THE TURN AT FROGO ON THE DEP. SOMEWHERE PAST FROGO; CTR ASKED US IF WE WERE TURNING TOWARD FRIANT; WHICH WE IMMEDIATELY STARTED. THE DISTR CAUSED BY THE HYD PROB CAUSED A BREAKDOWN IN PROCS BY BOTH OF US. I FORGOT TO ENGAGE THE LNAV; THE FO DID NOT TURN HIS COURSE SELECTOR AND CHANGE VOR FREQS FOR THE TURN AT FROGO. A CONTRIBUTING FACTOR FOR ME WAS THE VERY EARLY CHK IN AND A VERY POOR NIGHT'S SLEEP.