What was found
CENTER TANK FUEL QUANTITY INDICATOR INTERMITTENTLY INOP AFTER REACHING ZERO LBS. GROUNDED-YES. ACCOMPLISHED A TANK AND COMPENSATOR UNITS TEST, REF B737-900 AMM 28-41-21-710-801. NO DEFECTS NOTED. PERFORMED RING-OUTS BETWEEN D11316 (CENTER TANK BUSSING PLUG) AND D485 (CEILING J-BOX IN WHEEL WELL), REF B737-900 WDM 28-41-11. NO DEFECTS NOTED. FQIS FAULT HISTORY SHOWS 14 INSTANCES OF FAULT 28-41309, PROCESSOR FAILED, AND FLIGHT DECK EFFECT OF CENTER QTY BLANK. REPLACED FQIS PROCESSOR, REF AMM 28-41-81/401. OP CHECKS GOOD.