FLC B737-200 HAS LOST COM AFTER TKOF. THEY SQUAWK 7500 INSTEAD OF 7600. ABLE TO RESTORE THE COM PRIOR TO DSCNT.

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I; THE CAPT; WAS FLYING THE ACFT AS WE DEPARTED SHV FOR DFW. THE WX WAS SOLID IFR WITH MODERATE RAIN DURING OUR INITIAL CLB. WE WERE ASSIGNED BY DEP TO CLB TO 12000 FT AND FLY 290 DEGS TO INTERCEPT THE GGG 253 DEG RADIAL ON THE CEDAR CREEK ARR TO DFW. AT APPROX 11000 FT; DEP HANDED US OFF TO CTR. UPON ATTEMPTING TO CONTACT; WE EXPERIENCED TOTAL COMS FAILURE. THE FO FIRST TRIED THE LAST FREQ; THEN TRIED COM #2; TURNED ALL VOLUMES FULL UP; AND RESET CIRCUIT BREAKERS. WE THEN TRIED ISOLATING OUR MIKES AND HEADSETS; INCLUDING THE OXYGEN MASKS. ALL NAV RECEIVERS AND ASSOCIATED AUDIO WERE OPERATING NORMALLY. AT THIS TIME WE HAD BEEN WITHOUT COM FOR ABOUT 5 MINS AND THE FO SUGGESTED WE SQUAWK LOST COM; AND I AGREED. WE WERE GIVEN AN EXPECT FL200 10 MINS AFTER DEP ON OUR INITIAL CLRNC SO AT THAT TIME; BASED ON OUR ACARS OFF TIME; WE COMMENCED OUR CLB TO FL200 AND CONTINUED ON WITH THE CEDAR CREEK ARR. I THEN SUGGESTED TO THE FO THAT HE CHK THE 'BOOK' FOR A REVIEW OF APPLICABLE PROCS. I SAID THERE WAS A SECTION IN THE EMER SECTION ABOUT LOST COM. THIS IS WHERE I SHOULD HAVE BEEN MORE EXPLICIT AND SAID CHK THE FLT OPS MANUAL; GIVEN HIM MINE AS HE IS NOT REQUIRED TO HAVE ONE; AS IT PROBABLY WOULD HAVE ELIMINATED A FUTURE EMBARRASSMENT. INSTEAD HE DID THE POM COM/RAD PROC; WHICH WAS ALSO APPROPRIATE; IN AN ATTEMPT TO USE THE ACARS RADIO. THAT PROC DOES NOT APPEAR TO BE APPLICABLE TO OUR ACFT; AS IT DOES NOT HAVE A VHF 3 POS ON THE AUDIO PANEL. A TOUCHSCREEN ACARS WOULD HAVE BEEN A WONDERFUL THING; ASSUMING IT WOULD HAVE WORKED UNDER THIS CIRCUMSTANCE. NONETHELESS; THE FO HAD EXCELLENT KNOWLEDGE OF LOST COM NAV PROCS; WAS VERY DELIBERATE IN HIS ACTIONS AND TROUBLESHOOTING SKILLS. I FELT THE EMER WAS BEING HANDLED EFFICIENTLY AND THERE WAS NO REASON TO XFER THE CTL OF THE ACFT. NEITHER ONE OF US FELT OVERLOADED AND WE WERE CONFIDENT OF OUR DECISIONS. ABOUT 10 MINS INTO THE EMER; WE BECAME RESIGNED TO THE FACT THAT WE WOULD PROBABLY HAVE TO CONDUCT THE REMAINDER OF THE FLT LOST COM. WE MADE A PLAN OF OUR INTENTIONS AND THE FO BROADCAST THEM IN THE BLIND IN HOPES THAT POSSIBLY ATC MIGHT BE RECEIVING US. WE CALLED THE 'A' FLT ATTENDANT TO THE COCKPIT AND TOLD HER OF THE PROB AND TO EXPECT EMER EQUIP AS WE ARRIVED; BUT ASSURED HER THAT THE ACFT WAS FLYING NORMALLY; THAT WE COULD NAV; THAT ATC WOULD PROVIDE ADEQUATE SEPARATION; AND THAT WE HAD CLR PROCS FOR THIS TYPE OF EVENT. AS WE APCHED CEDAR CREEK VOR ON THE ARR AND IN THE DSCNT FOR THE SOUSA RESTR; THE FO SUGGESTED WE START THE APU SO WE COULD SEE IF XFERRING SOURCES MIGHT HELP. I CONCURRED; AND UPON XFERRING THE R ELECTRICAL BUS TO THE APU; COM WAS RESTORED. WE CALLED DFW APCH AS WE APCHED SOUSA AND ADVISED WE HAD LOST COM FOR ABOUT THE LAST 20 MINS; BUT ALL WAS NOW OPERATING NORMALLY. THE CTLR SIMPLY CLRED US TO A LOWER ALT AND GAVE US A VECTOR FOR AN ILS TO RWY 35R. THE FO ASKED IF WE SHOULD SWITCH BACK TO OUR NORMAL SQUAWK AND HE SAID NO; WE WERE FINE. UPON SWITCHING TO THE NEXT CTLR HE QUERIED US TWICE ABOUT OUR SQUAWK OF 7500. THE FO RESPONDED THAT WE HAD A COM FAILURE BUT THAT ALL WAS FINE NOW. THEY ASKED IF WE REQUESTED ASSISTANCE AND THE FO RESPONDED NO; AND THAT WE WERE JUST PLANNING ON LNDG AND TAXIING TO THE GATE. NOW WAS THE TIME I REALIZED THE ONE THING WE DIDN'T GET RIGHT -- THE LOST COM SQUAWK IS 7600! OBVIOUSLY THIS CREATED A BIT OF A STIR BUT FORTUNATELY WE WERE ABLE TO DEFUSE IT BEFORE IT WENT VERY FAR. IF WE WOULD HAVE HAD A LITTLE LONGER FLT I'M SURE WE WOULD HAVE FOUND OUR ERROR OURSELVES AS WE WERE JUST ABOUT TO REVIEW ALL THAT WE HAD DONE WHEN WE GOT THE RADIOS BACK. AT THAT TIME WE THOUGHT THE EMER WAS OVER AND PRESSED ON. APPARENTLY THE FAA WAS FINE WITH OUR LOST COM PROCS AND ONLY CONCERNED WITH THE POSSIBILITY OF HIJACKING.