(5)  
If two or more probe heaters have failed, the EICAS display shows the advisory message PROBE HEAT. The individual probe heat failure messages are not displayed. (This applies to any two probe heater failures in the entire system. Included are pitot, angle of attack, and total air temperature probes.)

 B. Ground Test (Fig. 2)
 (1)  The AOA probe heaters are tested on the ground with the engines off. This is done by the WING ANTI-ICE WINDOW/PROBE HEAT switch on the miscellaneous test panel. The switch is a momentary action, center off type. Holding the switch in the WINDOW/PROBE HEAT position energizes the left and right PROBE HT TEST relays. (The left PROBE HT TEST relay is in P33. The right PROBE HT TEST relay is in P37.) This provides a path for 115v ac power to flow through the AOA probe heaters. The CSRs energize, removing ground paths for the AOA lights on the auxiliary annunciator panel. If all heaters are working right, neither AOA light on P5 is on. If a probe heater fails the test, its amber probe heater light comes on. When the switch is released after testing, the system returns to normal ground operation. (The WINDOW/PROBE HEAT switch position tests all other probe heaters also.)
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757
MAINTENANCE MANUAL

 C. Control
 (1)  
To place system in operation, apply electrical power (Ref 24-22-00).

 (2)  
Check that R AOA HEAT and L AOA HEAT circuit breakers on main power distribution panel P6 are closed.

 (3)  
Check that PROBE HEAT IND AOA R and PROBE HEAT IND AOA L circuit breakers on overhead circuit breaker panel P11 are closed.

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757 FAULT ISOLATION/MAINT MANUAL
ANGLE OF ATTACK PROBE HEAT SYSTEM
COMPONENT  SHT 102 FIG.  QTY  ACCESS/AREA  REFERENCE AMM 
CIRCUIT BREAKER - FLT COMPT, P6 
L AOA HEAT, C1134 1  6L17  *
 R AOA HEAT, C1135CIRCUIT BREAKER - 1  6L23 FLT COMPT, P11  *
 PROBE HEAT IND AOA LEFT, C4194 1  11D5 OR 11R181  *
 PROBE HEAT IND AOA R, C4195 L EICAS, M10181 R EICAS, M10182COMPUTER - (FIM 31-41-00/101)  1  11R27  *
LIGHT - L AOA, L7 1  1  M10394 FLT COMPT, P5, MISC ANNUN PNL,  *
　
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