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Patient 1
THE CUSTOMER DID NOT HAVE A SERVICE HISTORY FOR THIS DEVICE, AND THERE WAS NO RECORD OF THE UNIT EVER BEING RETURNED TO NATUS FOR REPAIR OR SERVICE. VERY LITTLE DUST WAS OBSERVED IN THE UNIT, AND THE AIR INLET FILTER WAS MISSING. WHEN MEASURED, THE RESISTANCE OF THE HEATING COIL WAS WITHIN THE SPECIFICATION RESISTANCE RANGE OF 72 +/- 2 OHMS FOR THIS HEATING COIL. THE WARM SCALE COVER WAS THEN REMOVED AND THE INTERNAL ELECTRONICS, INCLUDING FUSES, PCAS, WIRING, BATTERY AND CONNECTIONS WERE ALL CHECKED FOR SIGNS OF OBVIOUS DAMAGE OR HEAT STRESS. OTHER THAN THE HEATING COIL, NO OTHER INTERNAL DAMAGE WAS OBSERVED. THE UNIT WAS THEN POWERED ON BRIEFLY, AND IT WAS CONFIRMED THAT PROPER VOLTAGES WERE BEING APPLIED TO THE VARIOUS PCAS. NO OVERHEATING AND/OR ODORS WERE DETECTED. THE DAMAGED/STRESSED HEATER ELEMENT SHOWED BOTH ELONGATION AND SAGGING OF THE HEATER COILS. THE HEATER COIL ELONGATION RESULTED IN THE FAILURE OF THE UNIT TO REGULATE THE TEMPERATURE OF THE NEWBORN WARMING SHELF TO THE EXPECTED TEMPERATURE OF APPROXIMATELY 93 DEGREES FAHRENHEIT. RUNNING UNDER STEADY-STATE CONDITIONS, THE PLASTIC WARMING SHELF REACHED A TEMPERATURE OF 129.6 DEGREES FAHRENHEIT WITHOUT THE FAN FILTER, AS RECEIVED FROM CUSTOMER. WHEN THE FILTER WAS INSTALLED, THE STEADY-STATE TEMPERATURE OF THE SHELF REACHED 141 DEGREES FAHRENHEIT. IT WAS OBSERVED THAT AFTER REACHING STEADY-STATE, THE WARM SCALE CONTINUOUSLY SUPPLIED POWER TO THE HEATING COIL. THIS CAN BE EXPLAINED BY THE FACT THAT THE HEATING COILS WERE SPACED MUCH FURTHER APART IN THE REGION OF THE THERMISTOR SENSOR ASSEMBLY THAN IN THE REGIONS WHERE THERMOCOUPLES WERE LOCATED, RESULTING IN A SENSED AIR TEMPERATURE OF APPROXIMATELY 79 DEGREES F, WITHOUT AIR FILTER AND 80.5 DEGREES F WITH THE AIR FILTER. THIS TEMPERATURE IS NOT HIGH ENOUGH REGULATE THE NEW BORN SHELF TEMPERATURE TO 93 DEGREES F AS SUGGESTED IN THE INSTRUCTION MANUAL OR TO TRIP THE OVER-TEMPERATURE CUTOFF VALUE OF 103 DEGREES. THIS MALFUNCTION IS THE RESULT OF HEATING COIL ELONGATION IN THE AREA OF THE THERMISTOR SENSOR ASSEMBLY. THE SUBJECT DEVICE HAS BEEN SCRAPPED AND GIVEN TO NATUS QA FOR ANALYSIS AND ROOT CAUSE INVESTIGATION. THE CUSTOMER HAS BEEN PROVIDED A REPLACEMENT UNIT. NATUS IS CURRENTLY CONDUCTING AN ONGOING INVESTIGATION INTO THIS MALFUNCTION AND WILL FOLLOW UP WITH SUPPLEMENTAL REPORTS AS ADDITIONAL INFORMATION IS OBTAINED.